L Lamellar Copolymers Mario Malinconico Research Director, Institute for Polymers, Composites and Biomaterials (IPCB-CNR), Pozzuoli, Naples, Italy The presence of covalent bonds between the blocks in block copolymers leads to severe restrictions on the state of local segregation between them allowing the formation of few and defined morphologies. Comparing the phase separation that occurs in a pure copolymer AB and into the corresponding mixture of homopolymers HA/HB and assuming that in both cases strips of different phases are formed, parallel to the surface of the system, it is observed that in the mixture the size of the homopolymeric lamellae parallel to the surface and perpendicular to it are both much greater than the radius of gyration (Rg) of the polymer. Instead, in the case of the block copolymer, the presence of the bond between the blocks allows the formation of lamellae whose dimensions parallel to the surface are much greater than the radius of gyration, but the size perpendicular to the surface has dimensions comparable to the radius of gyration. On the basis of this different structural feature, the domains of different compositions which are formed in a mixture of homopolymers are named macrophases, while in the case of a copolymer are spoken of microphases or even, sometimes, of nanophases (Fig. 1). # Springer-Verlag Berlin Heidelberg 2016 E. Drioli, L. Giorno (eds.), Encyclopedia of Membranes, DOI 10.1007/978-3-662-44324-8 There are numerous methods for inducing the orientation and order of large-scale morphologies of the copolymers blocks, such as lamellae. Some main strategies used are reported: • Fields of mechanical flow (extrusion (Keller et al. 1970; Folkes et al. 1973), compression (Kofinas and Cohen 1995; Drzal et al. 2001; Quiram et al. 1998; van Asselen et al. 2004), flows involving oscillating (Skoulios 1977; Hadziioannou et al. 1979, p. 15, 1979, p. 136; Morrison and Winter 1989; Morrison et al. 1990; Wiesner 1997; Scott Pinheiro and Winey 1998; Leist et al. 1999; Hermel et al. 2002; Stangler and Abetz 2003; Wu et al. 2004) or stationary (Sebastian et al. 2002;;Angelescu et al. 2004, 2005; Luo and Yang 2004) shear, or techniques that combine different flow fields (Albalak and Thomas 1993, 1994; Honeker et al. 2000; Dair et al. 2000; Villar et al. 2002)) were successfully used to induce alignment in block copolymers. • Magnetic fields induce orientation in liquid crystalline block copolymers (Osuji et al. 2004; Tomikawa et al. 2005) and block copolymers with a crystallizable block through an accurate control of the crystallization process (Grigorova et al. 2005). • Static electric fields have been widely used to guide macroscopically cylindrical and lamellar morphologies in the melt of such copolymers (Morkved et al. 1996; Onuki and Fukuda 1995; 1084 Lamellar Copolymers Lamellar Copolymers, Fig. 1 Phase separation in block copolymers (a) and in homopolymers blend (b) (Schulz and Bates 1996) Thurn-Albrecht et al. 2000, 2002; Elhadj et al. 2003; Xu et al. 2004; DeRouchey et al. 2004; Xiang et al. 2004). • Solvent evaporation allows the orientation of lamellar microdomains perpendicularly to the film surface (Turturro et al. 1995; Kim and Libera 1998, p. 2569, 1998, p. 2670). After the deposition, the glass transition temperature (Tg) of the film swollen with a solvent is below the ambient temperature, allowing free mobility of the chains. With increasing concentration of the solvent, the copolymer undergoes a transition from the disordered state to the ordered. The diffusion of the solvent in the thin film produces a concentration gradient so that order spreads rapidly from the surface of the film to the substrate. The consequent decrease of Tg below room temperature, for at least one block, freezes the structures that, due to the high directionality of the solvent gradient, organize into domains with lamellar axes perpendicular to the surface (Kim et al. 2004; Kimura et al. 2003; Lin et al. 2002; Temple et al. 2003). A great potential of the block copolymers is represented by the possibility of using the ordered nanostructures formed by self-assembly as a matrix (host) for the inclusion of guest molecules (guest) and dispersion of different types of Lamellar Copolymers 1085 Lamellar Copolymers, Fig. 2 Bright-field TEM image of a thin film of a lamellar block copolymer polystyrene-poly(ethyleneco-propylene) in which gold nanoparticles suitably passivated are included only in the layers of polystyrene (Bockstaller et al. 2005) nanoparticles, in order to obtain nanocomposites with special physical properties. The nanocomposites represent a class of composite materials consisting of matrix and a polymeric particle reinforcement having at least one dimension of the order of nano; such particle reinforcements are called nanofillers or nanoreinforcement. The different microdomain nanostructures generated by block copolymers (lamellae in particular, but also spheres or cylinders) act as host to sequester selectively nanofillers (guest) with a suitable chemical and geometrical affinity. The great innovation of these studies consists in the fact that the use as a matrix of block copolymers, then nanostructured materials already, instead of homopolymers, offers an important opportunity to control the distribution of spatial and orientational nanofillers. The nanoparticles, which induce specific properties, are not, in fact, randomly distributed in the polymer matrix but are sequestered in ordered microdomains and, thus, distributed in an orderly manner in the matrix. This allows a greater control of the final physical properties of the nanocomposites. A TEM image of a thin film of a nanocomposite based on a lamellar block copolymer in which gold nanoparticles are distributed in such an ordered way only in specific layers of the structure is shown in Fig. 2 (Bockstaller et al. 2005). References Albalak RJ, Thomas EL (1993) Microphase separation of BCP solutions in a flow field. J Polym Sci Polym Phys 31:37 Albalak RJ, Thomas EL (1994) Roll casting of BCPs and BCP-homopolymer blends. J Polym Sci Polym Phys 32:341 Angelescu DE, Waller JH, Adamson DH, Deshpande P, Chou SY, Register RA, Chaikin PM (2004) Macroscopic orientation of block copolymer cylinders in single-layer films by shearing. Adv Mater 16:1736 Angelescu DE, Waller JH, Register RA, Chaikin PM (2005) Shear-Induced alignment in thin films of spherical nanodomains. Adv Mater 17:1878 Bockstaller M, Mickievic RA, Thomas EL (2005) Block copolymer nanocomposites: perspectives for tailored functional materials. Adv Mater 17:1331 Dair BJ, Avgeropoulos A, Hadjichristidis N, Capel M, Thomas EL (2000) Oriented double gyroid films via roll casting. Polymer 41:6231 DeRouchey J, Thurn-Albrecht T, Russell TP, Kolb R (2004) Block copolymer domain reorientation in an electric field: An in-situ small-angle X-ray scattering study. Macromolecules 37:2538 Drzal PL, Barnes JD, Kofinas P (2001) Path dependent microstructure orientation during strain compression of semicrystalline block copolymers. Polymer 42:5633 Elhadj S, Woody JW, Niu VS, Saraf RF (2003) Orientation of self-assembled block copolymer cylinders perpendicular to electric field in mesoscale film. Appl Phys Lett 82:871 Folkes MJ, Keller A, Scalisi FP (1973) Extrusion technique for the preparation of single crystals of block copolymers. Colloid Polym Sci 251:1 Grigorova T, Pispas S, Hadjichristidis N, Thurn-Albrecht T (2005) Magnetic field induced orientation in diblock copolymers with one crystallizable block. Macromolecules 38:7430 Hadziioannou G, Mathis A, Skoulios A (1979) Monocristaux de copolymères triséquencés styrène/ isoprène/styrène présentant la structure cylindrique: I. Étude de l'orientation par diffraction des rayons X aux petits angles. Colloid Polym Sci 257:15, 136 Hermel TJ, Wu LF, Hahn SF, Lodge TP, Bates FS (2002) Shear-induced lamellae alignment in matched triblock and pentablock copolymers. Macromolecules 35:4685 Honeker CC, Thomas EL, Albalak RJ, Hajduk DA, Gruner SM, Capel MC (2000) Perpendicular deformation of a near-single-crystal triblock copolymer with a L 1086 cylindrical morphology. 1. Synchrotron SAXS. Macromolecules 33:9395 Keller A, Pedemonte E, Willmouth FM (1970) Macrolattice from Segregated Amorphous Phases of a Three Block Copolymer. Nature (London) 225:538 Kim G, Libera M (1998) Morphological development in solvent-cast polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer thin films. Macromolecules 31:2569, 2670 Kim SH, Misner MJ, Xu T, Kimura M, Russell TP (2004) Highly oriented and ordered arrays from block copolymers via solvent evaporation. Adv Mater 16:226 Kimura M, Misner MJ, Xu T, Kim SH, Russell TP (2003) Long-Range ordering of diblock copolymers induced by droplet pinning. Langmuir 19:9910 Kofinas P, Cohen RE (1995) Melt processing of semicrystalline E/EP/E triblock copolymers near the order-disorder transition. Macromolecules 28:336l Leist H, Maring D, Thurn-Albrecht T, Wiesner U (1999) Double flip of orientation for a lamellar diblock copolymer under shear. J Chem Phys 110:8225 Lin Z, Kim DH, Wu X, Boosahda L, Stone D, LaRose L, Russell TP (2002) A rapid route to arrays of nanostructures in thin films. Adv Mater 14:1373 Luo KF, Yang YL (2004) Orientation phase transition in the hexagonal phase and rheological properties of diblock copolymer under a simple shear flow. Polymer 45:6745 Morkved TL, Lu M, Urbas AM, Ehrichs EE, Jaeger HM, Mansky P, Russell TP (1996) Local control of microdomain orientation in diblock copolymer thin films with electric fields. Science 273:931 Morrison FA, Winter HH (1989) Effect of unidirectional shear on the structure of triblock copolymers. 1. Polystyrene-polybutadiene-polystyrene. Macromolecules 22:3533 Morrison FA, Winter HH, Gronski W, Barnes JD (1990) Effect of unidirectional shear on the structure of triblock copolymers. 2. Polystyrene-polyisoprenepolystyrene. Macromolecules 23:7200 Onuki A, Fukuda J (1995) Electric field effects and form birefringence in diblock copolymers. Macromolecules 28:8788 Osuji C, Ferreira PJ, Mao G, Ober CK, Vander Sande JB, Thomas EL (2004) Alignment of self-assembled hierarchical microstructure in liquid crystalline diblock copolymers using high magnetic fields. Macromolecules 37:9903 Quiram DJ, Register RA, Marchand GR, Adamson DH (1998) Chain orientation in block copolymers exhibiting cylindrically confined crystallization. Macromolecules 31:4891 Schulz MF and Bates FS (1996) In “Physical properties of polymers handbook”, American Institute of Physics. pp 427–433 Scott Pinheiro B, Winey KI (1998) Mixed parallel–perpendicular morphologies in diblock Lamellar Copolymers copolymer systems correlated to the linear viscoelastic properties of the parallel and perpendicular morphologies. Macromolecules 31:4447 Sebastian JM, Graessley WW, Register RA (2002) Steady-shear rheology of block copolymer melts and concentrated solutions: Defect-mediated flow at low stresses in body-centered-cubic systems. J Rheol 46:863 Skoulios A (1977) Properties of oriented block copolymers. J Polym Sci Polym Symp 58:369 Stangler S, Abetz V (2003) Orientation behavior of AB and ABC block copolymers under large amplitude oscillatory shear flow. Rheol Acta 42:569 Temple K, Kulbaba K, Power-Billard KN, Manners I, Leach KA, Xu T, Russell TP, Hawker CJ (2003) Spontaneous vertical ordering and pyrolytic formation of nanoscopic ceramic patterns from poly (styrene-b-ferrocenylsilane) Advanced Materials. 15: 297-300 Thurn-Albrecht T, Steiner R, DeRouchey J, Stafford CM, Huang E, Bal M, Tuominen M, Hawker CJ, Russell TP (2000) Nanoscopic templates from oriented block copolymer films. Adv Mater 12:787 Thurn-Albrecht T, DeRouchey J, Russell TP, Kolb R (2002) Pathways toward electric field induced alignment of block copolymers. Macromolecules 35:8106 Tomikawa N, Lu ZB, Itoh T, Imrie CT, Adachi M, Tokita M, Watanabe J (2005) Orientation of microphase-segregated cylinders in liquid crystalline diblock copolymer by magnetic field. Jpn J Appl Phys 2 44:L711 Turturro A, Gattiglia E, Vacca P, Viola GT (1995) Free surface morphology of block copolymers: 1. Styrene-butadiene diblock copolymers. Polymer 21:3987 van Asselen OLJ, van Casteren IA, Goossens JGP, Meijer HEH (2004) Deformation behavior of triblock copolymers based on polystyrene: an FT-IR spectroscopy study. Macromol Symp 205:85 Villar MA, Rueda DR, Ania F, Thomas EL (2002) Study of oriented block copolymers films obtained by roll-casting. Polymer 43:5139 Wiesner U (1997) Lamellar diblock copolymer under large amplitude oscillatory shear flow: order and dynamics. Macromol Chem Phys 198:3319 Wu L, Lodge TP, Bates FS (2004) SANS determination of chain conformation in perpendicular-aligned undecablock copolymer lamellae. Macromolecules 37:8184 Xiang H, Lin Y, Russell TP, Kolb R (2004) Electrically induced patterning in block copolymer films. Macromolecules 37:5358 Xu T, Zhu Y, Gido SP, Russell TP (2004) Electric field alignment of symmetric diblock copolymer thin films. Macromolecules 37:2625 Langerhans Islet Langerhans Islet Loredana De Bartolo and Antonietta Messina Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy The islets of Langerhans are endocrine cell cluster well ordered in lobules, of 0.3–0.7 mm in diameter, containing from 3,000 to 4,000 cells, and located mainly in the tail region of the pancreatic gland. Discovered in 1869, though representing only 2 % of the whole organ, they serve to coordinate the physiological control of the glycemic values in the blood. Five different hormone-secreting cell types constitute the islets’ cytoarchitecture: alpha cells producing glucagon, beta cells producing insulin and amylin, delta cells producing somatostatin, PP cells (gamma cells) producing the pancreatic polypeptide, and epsilon cells producing ghrelin. In human beings, the alpha and beta cells are in close relationship with each other. Representing nearly 90 % of the total islet cells, their secretive activity is modulated by the blood glucose levels: when low concentrations of sugar are detected, the islets respond with the glucagon secretion to induce the glucose release from the hepatic deposits into the bloodstream. After a meal the high concentration of the blood sugars causes the beta cell activation determining the insulin-induced glucose metabolism and the production of the energy requested by the body. Since the interaction between the hormonesecreting cells of the islets and the paracrine, electric, and nervous-regulating factors is highly complex, the tiniest decompensation in the islet cells’ functions, modulation, and survival can result in the onset of severe pathologies and organic disorders, which leads patients to severe complications and a high risk of death. Actually, 98 % of the diseases involving the pancreas referred to the loss of the ability in modulating the food sugars’ conversion into energy, due to the malfunctioning or destruction of the 1087 insulin-producing beta cells by autoimmune responses. Thus, sustaining and/or replacing malfunctioning islets is the only therapeutic approach in order to induce the partial recovery of the metabolic functions in the patients (Patel et al. 2014). Before 1893 and the discovery of the pancreas involved in the income of the diabetes, starving was the only treatment possible for people suffering for diabetes. Then, first attempts in the development of grafts were made using deceased donor’s islets serving as substitutes for the malfunctioning pancreas. Many patients showed a partial recovery; however, after transplantation, these islet grafts were inevitably destroyed due to the immune and inflammatory reaction in the hosts. In truth, despite the risk/ benefit trade being quite high for the patients, the transplantation still remains the only therapeutically approved approach to gain the patients recovery of the pancreatic activity. Allo and autotransplantation are nowadays performed through the infusion of purified islets into the portal vein of the liver, and 50 % of the receivers are able to regain the pancreatic functionality and recover from the systemic complications in 1 year. However, the number of available and compatible donors is quite limited, and the lifetime immunosuppression therapy exposes the patient to infections, diseases, and harmful side effects. Thus, new techniques labeled as tissue engineering approaches have been developed to overcome these disadvantages and foresee the use of polymeric membrane systems to produce engineered device containing islets of insulin-producing cells, to control the release of the cell products from the islets, their sustainment, and their protection from the immunoreactive species in the site of implantation. Coordinated by local drug delivery systems, consisting in boles of low-dose anti-rejection drugs able to minimize the immune response as well as any inflammatory effects at the site of implantation, the encapsulation technique is the most promising method. The islets are wrapped in a tight coating made of biocompatible polymers acting as a perm-selectivity membrane that serves to mimic the heterogeneous and safe L 1088 environment where oxygen and nutrient perfusion is provided continuously and appropriate space and ECM-like physical and mechanical support, essential for the correct insulin production and secretion and the islets’ survival, are provided. Different classes of encapsulating devices are available and classified depending on their size in macro-, micro-, and nano-devices. Classified as extravascular diffusion devices when placed subcutaneously or in the peritoneal cavity and intravascular diffusion system, three macrodevices have been approved for the clinical trials: the TheraCyte system, made up of two composite Teflon-based membranes in between the islets are placed; the Islet Sheet device, constituted by supported alginate sheets containing the pancreatic islets; and the Beta O2 device able to increase the oxygen exchange in the implantation site being made of oxygen-generating biomaterial able to deliver locally the oxygen to the cells. Additional macrodevices consist of tubular porous membranes filled with islets generally placed into the vessels, where adequate kinetic properties allowed the insulin release straight into the blood stream. Micro devices constituted by single cluster of beta cells incorporate into semipermeable polymeric membranes, and nano-devices are nowadays under investigation in a few animal models. They differ generally on the processing methods used for the encapsulation of the islets and both allow to increase the insulin release rate and the oxygen exchange into the islets. The micro systems are processed in a spherical system of alginate hydrogels coated with poly-ornithine and polylysine or by cross-linking a thin hydrogel sheet onto an islet cluster by the conformal coating methods, whereas the nanodevices (1–100 mm) consist of islets encapsulated by alternating charged polylysine, polyglutamic acid, and PEG-biotin polymers over the cell aggregate surface through the layer-by-layer method. The decreased thickness of the capsules obtained by covering the islets with a single sheet of molecules increases and improves the insulin release kinetics after implantation and resulting as well in higher diffusion of nutrients in the core of the cell clusters. Independently on the size of the device, three different encapsulated Langerhans Islet replacement strategies are available for the implantation: All-In/Biodegrade-Out replacement, made of biodegradable components easily absorbed by the body; All-In/All-Out replacement, designed to not react with the host tissues as the cytotherapeutics devices, the islet sheet medical devices, and the beta-O2 device; and Flush/Reload replacement used for the macrodevices designed in order to grow into the host to provide a vascular interface (David and Marchetti 2014). New cell sources. To overcome the shortage of donor organs and the side effect linked to the autoimmune destruction of the patient islets as for diabetes type I, alternative sources of beta cells have been researched. The adult stem cells or progenitor cells appear to be the most promising. Through reprogramming cell strategy (transdifferentiation), pancreatic precursor cells are reprogrammed in insulin-producing cells. Moreover, the own patients pancreas exocrine cells and the skin cells that can undergo to the reprogrammation technique representing a promising new source for the beta cells supply, being not needed the immunosuppression therapy after the implant (DomìnguezBendala et al. 2013). Therefore, another potential source of beta cells may be the xenotransplantation with pig pancreas cells. Interestingly, human and porcine insulin differ only for one amino acid, and insulin extracted from porcine pancreas has been used for the treatment of patients with diabetes before the development of recombinant human insulin technology. However, several problems need to be overcome for porcine islet transplantation to become a viable clinical option; however, studies in rodents and large animals have shown great promise that justifies cautious optimism for the near future. In the last years, another chance to improve the tissue engineering of the pancreas appears to be the prevention of the inflammation at the site of the transplant, co-transplanting mesenchymal stem cells. The MSCs that have been demonstrated offer natural defenses by blocking the signals of the immune responses, limiting inflammation, stimulating the blood vessel growth, and promoting the long-term function of islets due to their trophic effects. Up until now, though the most important progress in the pancreatic islet transplantation is Layer-by-Layer (LbL) Method settled in preclinical trials and only one lead research project has been presented in the last years on baboons, 95 % of the patients who received the capsule implantation resulted in considerable improvements of the glucose metabolism with the reverse of the main diabetes side effects at 1 year and more than 80 % at 5 years after implants opening new hopes in the further improvement of new strategies for the diabetes treatment in the nearest future. References David SW, Marchetti P (2014) Encapsulated islets for diabetes therapy: history, current progress, and critical issues requiring solution. Adv Drug Deliv Rev 67–68:35–73 Domìnguez-Bendala J, Pileggi A, Ricordi C (2013) Islet cell therapy and pancreatic stem cells, Chapter 70. In: Atala A, Lanza R (eds) Handbook of stem cells, 2nd edn. Academic, New York, pp 835–853 Patel T, Salvatori M, Hemal S et al (2014) Pancreatic islets regeneration: the bioengineering approach, Chapter 41. In: Orlando G, Lerut JP, Soker S, Stratta RJ (eds) Regenerative medicine applications in organ transplantation, 1st edn. Academic, New York, pp 599–607 Langmuir and Langmuir–Blodgett (LB) Films Osvaldo N. Oliveira Jr and Diogo Volpati Sao Carlos Institute of Physics – IFSC, University of Sao Paulo – USP, Sao Paulo, Brazil An ultrathin, resistant layer can be formed at the air-water interface by spreading a single drop of oil. This phenomenon was discovered centuries ago, but it was Irving Langmuir that in the early twentieth century established sound theoretical and experimental basis for their study (Langmuir 1917). The now-called Langmuir monolayers are formed at air-water interfaces using an experimental system known as Langmuir trough. Basically a solution containing amphiphilic molecules 1089 (with both hydrophobic and hydrophilic parts) is spread over at the air-water interface. The hydrophilic parts allow the spreading of the molecules while the hydrophobic parts do not let the molecules dissolve into subphase. Movable barriers are used to compress the monolayer. The presence of the monolayer can be detected easily by measuring the surface pressure (p), which is the decrease in surface tension, as the monolayer is compressed, thus leading to pressure-area isotherms. In the 1930s, Katharine Blodgett – then an assistant to Langmuir – developed the procedures to transfer the monolayer onto a solid substrate (Blodgett and Langmuir 1937). The deposited films are now termed Langmuir-Blodgett films. Basically, monolayers can be transferred by immersing (or withdrawing) the substrate into (or from) the liquid while the monolayer is adsorbed homogeneously at the substrate. Thus, well-ordered films with very accurate thickness can be formed. References Blodgett KD, Langmuir I (1937) Built-up films of barium stearate and their optical properties. Phys Rev 51:0964–0982 Langmuir I (1917) The constitution and fundamental properties of solids and liquids. II Liquids. J Am Chem Soc 39:1848–1906 Layer-by-Layer (LbL) Method Saren Qi1 and Chuyang Y. Tang2 Singapore Membrane Technology Centre, Nanyang Technological University, Singapore, Singapore 2 Department of Civil Engineering, The University of Hong Kong, Hong Kong, Hong Kong SAR 1 Layer-by-layer (LbL) method (also known as LbL assembly, electrostatic self-assembly (ESA), or polyelectrolyte multilayer (PEM) technology) is L 1090 Layer-by-Layer (LbL) Method Layer-by-Layer (LbL) Method, Fig. 1 Simplified schematic of the film deposition process using LbL method a versatile method to form mutilayers on a solid support. The self-assembly method is driven by the electrostatic force between the precursor materials. Precursor materials to form mutilayers can be chosen from polyelectrolytes, biopolymers, clays, metal complex and their derivates, nanoparticles, dendrimers, and so on (Bertrand et al. 2000). The advantages of this method are the relatively simple process, independence of substrate properties (i.e., size, topology, materials, and so on), and formation of fuzzy structure. Therefore, LbL method has a potential to be applied in various applications including forming multicomposite films, nanoparticle modification, enzyme process, optic development, sensors, membrane for water treatment, fuel cell, and so on. The basic formation mechanism of a typical LbL process is shown in the schematic drawing in Fig. 1. Step (1) shows the absorption of polycation by a negatively charged substrate. After washing with deionized water (step (2)), the substrate was soaked in a polyanion solution (step (3)). Then, it is washed with deionized water (step (4)). These procedures can be repeated to prepare multilayers on the substrate. Other variations to this basic coating method includes spray (Schlenoff et al. 2000), spin (Chiarelli et al. 2001), hydrodynamic LbL deposition (Deng et al. 2008), electric field-induced LbL process (Zhang et al. 2008), and pressure-induced LbL process (Zhang et al. 2011). Characteristics of the LbL films are known to be highly affected by the preparation procedures and conditions. In addition to the substrate and multilayer materials, other main factors affecting LbL film properties include ionic strength of coating solution, solution pH, coating time, and the use of cross-linkers. Cross-References ▶ Cross-Linked Layer-by-Layer Membranes References Bertrand P, Jonas A, Laschewsky A, Legras R (2000) Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials, structure and properties. Macromol Rapid Commun 21(7):319–348 Chiarelli PA, Johal MS, Casson JL, Roberts JB, Robinson JM, Wang HL (2001) Controlled fabrication of polyelectrolyte multilayer thin films using spin-assembly. Adv Mater 13(15):1167 Deng HY, Xu YY, Zhu BK, Wei XZ, Liu F, Cui ZY (2008) Polyelectrolyte membranes prepared by dynamic self-assembly of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) for nanofiltration (I). J Membr Sci 323(1):125–133 Layer-by-Layer Self-Assembly Membrane Schlenoff JB, Dubas ST, Farhat T (2000) Sprayed polyelectrolyte multilayers. Langmuir 16(26):9968–9969 Zhang P, Qian J, Yang Y, An Q, Liu X, Gui Z (2008) Polyelectrolyte layer-by-layer self-assembly enhanced by electric field and their multilayer membranes for separating isopropanol-water mixtures. J Membr Sci 320(1–2):73–77 Zhang G, Dai L, Ji S (2011) Dynamic pressure-driven covalent assembly of inner skin hollow fiber multilayer membrane. AIChE J 57(10):2746–2754 Layer-by-Layer Self-Assembly Membrane Emma Piacentini and Lidietta Giorno Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy Layer-by-layer (LbL) self-assembly membranes are multilayered nanoarchitectures obtained by depositing oppositely charged polyelectrolytes or molecules presenting mutually interacting binding sites (Table 1) (Borges and Mano 2014). The LbL method can not only be applied to polymers but also on the combinations of polymers with particles. The LBL assembly based on electrostatic interaction is the most used and investigated method for multilayered nanoarchitecture construction. In this case, LbL self-assembly membranes are produced by simply repeating the alternate immersion of a charged substrate in the corresponding polyionic solution of opposite charge (Fig. 1). To speed up the deposition process, otherwise time consuming as a consequence of the necessity to wait several minutes between each step of adsorption and rinsing, spray deposition and spin coating have been demonstrated to be suitable. The method is very attractive due to its simplicity and efficiency in film preparation; however, the multilayer assemblies are less stable and robust than the ones obtained by hydrogen or covalent bonding. 1091 The LBL growth, structure, and properties of multilayer assemblies are influenced by several physicochemical parameters such as pH, ionic strength and electrolyte species, temperature, solvent quality, adsorption time, and the intrinsic properties of polyelectrolytes such as charge density, concentration, architecture, and molecular weight. Despite the several methods available for LBL assembly of multilayer films, the concept of LBL assembly based on multiple intermolecular interactions opens for a great variety of materials with well-defined properties in terms of thickness, compositions, structure, wettability, building, or charged/uncharged for a wide range of applications. Potential applications of LbL membranes are in biomedical field such as drug delivery, gene transfection, and biosensors (Yoon et al. 2014). The controlled drug delivery can be achieved using hydrolytically degradable polymers such as poly (b-amino ester). Gene transfection is obtained by using plasmid DNA as an anionic layer to form LbL films. Biosensors can be produced by using charged biomolecules such as glucose oxidase (able to catalyze glucose oxidation with simultaneous production of hydrogen peroxide) used as glucose sensor. LbL membranes can also be used in tissue engineering by introducing functional groups onto the surface of LbL membrane able to promote cell proliferation and differentiation as substrate or by using cells as a template of LbL systems. The LbL self-assembly technique has been explored in the development of electrochemical energy conversion and storage devices from fuel cells to supercapacitors (Xiang et al. 2012). Other recent applications include water treatment like water softening, desalination, and recovery of certain ions (Sanyal and Lee 2014). Advantages of LbL self-assembly technology include • Its simplicity and low cost • Variability of the applicable materials (conventional polyelectrolytes, water-soluble L 1092 Layer-by-Layer Self-Assembly Membrane Layer-by-Layer Self-Assembly Membrane, Table 1 Materials available for Layer-by-layer (LbL) self-assembly membranes Molecules Polyelectrolyte polymers Attractive Force Type Electrostatic interaction Polymers carrying hydrogen donor and acceptor moieties Hydrogen bonding Uncharged molecules Hydrophobic interactions Covalent bonding Molecules having complementary functional groups Stereoregular polymers carrying sites of opposite chirality Host (e.g., cyclodextrins, cucurbiturils, calixarenes, pillararenes, crown ethers, porphyrins) and guest (e.g., ferrocene, adamantane, azobenzene) molecules. Nonionic molecules, which present electron-accepting and electrondonating groups, respectively, in the side chains. Stereocomplexation Avidin and biotin-labeled polymers or Antibody Antigen conjugated molecules or lectin carbohydrate or DNA hybridization Metal ions and organic ligand Biologically specific interaction Examples Poly(styrenesulfonate) (PSS) Poly(allylamine hydrochloride) (PAH) Poly(L-lysine)/alginate (PLL/ALG) PLL/hyaluronan (PLL/HA) PLL/poly(L-glutamic acid) (PLL/ PGA), PLL/poly(acrylic acid) (PLL/PAA), PGA/PAH, chitosan/HA (CHT/HA), poly (ethylenimine)/PAA (PEI/ PAA) Poly(vinylpyrrolidone) (PVP) Poly(vinyl alcohol) (PVA) Poly(acrylamide) (PAA) Poly(ethylene oxide) (PEO) Poly(vinylpyrrolidone) (PVPON) Poly(methacrylic acid), PMAA Alkanethiols-proteins Poly(vinylamine-co-N-vinylisobutyramide) [Poly(VAm-co-NVIBA)] and PAA. Carboxyl group of PAA activated by 1-ethyl-3(3-(dimethylamino)propyl)Carbodiimide hydrochloride (EDC) and amine groups of poly(vinylamine-coN-vinylisobutyramide) Poly(VAm-co-NVIBA) (It-st)poly(methyl methacrylate) (PMMA) Host-guest interactions Cyclodextrin (b-CD) and adamantane Charge-transfer interaction Y[2-(9-carbazolyl)ethyl methacrylate] (PCzEMA, electron-donor polymer) and poly[2[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate] (PDNBMA, electron-acceptor polymer) Biotin protein conjugate and polymerized streptavidin on hydrophobic silica surfaces Coordination chemistry interactions proteins, charged polysaccharides, as well as charged inorganic substances, including colloidal nanoparticles, heteropolyacids, and metal nanoparticles) • Precise microstructural control and high repeatability Poly(copper styrene 4-sulfonate) (PSS(Cu)1/2), and PVP • Great control over the composition of the film along the vertical direction by changing the nature of the building blocks that are deposited during each step • Extensive possibility in wide range applications • Its nontoxic and environment-friendly nature Leather Industry 1093 1°Step: Immersion of the charged substrate in the polyionic solution - 1°Step 2°Step 2°Step: washing - + + + + + + + + 3°Step: Immersion of the charged substrate in the polyionic solution 3°Step 4°Step - + + + + + + + + 4°Step: washing - Layer-by-Layer Self-Assembly Membrane, Fig. 1 LbL self-assembled membranes buildup via electrostatic interactions References Borges J, Mano JF (2014) Molecular interactions driving the layer-by-layer assembly of multilayers. Chem Rev 114:8883–8942 Sanyal O, Lee I (2014) Recent progress in the applications of layer-by-layer assembly to the preparation of nanostructured ion-rejecting water purification membranes. J Nanosci Nanotechnol 14:2178–2189 Xiang Y, Lu S, Jiang SP (2012) Layer-by-layer self-assembly in the development of electrochemical energy conversion and storage devices from fuel cells to supercapacitors. Chem Soc Rev 41:7291–7321 Yoon H, Dell EJ, Freyer JL, Campos LM, Jang W (2014) Polymeric supramolecular assemblies based on multivalent ionic interactions for biomedical applications. Polymer 55:453e464 Leather Industry Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy In the leather industry, the animal rawhide is converted into finished leather, a durable and flexible material, through a series of chemical and mechanical treatments. The steps in the production of leather between curing (a salt treatment to prevent putrefaction of the collagen) and tanning (a treatment of leather stabilization with vegetable or mineral substances) are collectively referred to as beamhouse operations. They include, in order, soaking, unhairing/liming, deliming/bating, and pickling. All these processes are realized in chemical reactors (tumblers) in which the skins react with different chemicals (acids, alkalis, chromium salts, tannins, solvents, sulfides, dyes, auxiliaries, etc.) in aqueous solutions (Fig. 1). Wastewaters coming from different tanning operations contain high concentrations of organic and inorganic substances causing significant pollution phenomena. Organic pollutants come from the skins (it is calculated that the raw skin has 30 % loss of organic material during the working cycle), or they are introduced during the working cycle (e.g., tanning). Inorganic pollutants are a residual of the used chemicals (i.e., chromium salts) that are not completely fixed by the skins owing to the low efficiency of the operations (Cassano et al. 2001). L 1094 Leather Industry, Fig. 1 Scheme of tumbler Leather Industry, Degreasing water, skins, chemicals treated skins, exhausted liquor permeate water, surfactants, enzymes Retentate (emulsified fat for fat liquoring) bath feed tank UF Leather Industry, Degreasing, Fig. 1 Scheme of aqueous degreasing combined with ultrafiltration process References Cassano A, Molinari R, Romano M, Drioli E (2001) Treatment of aqueous effluents of the leather industry by membrane processes. A review. J Membr Sci 181:111–126 Leather Industry, Degreasing Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy In the degreasing step, fats and grease are removed from the interfibrillary spaces with the use of lipases, detergents, or solvents in order to allow the penetration of various tanning materials and dyes. This operation is necessary especially for sheepskins where the percentage of fat substances on raw weight is of about 30–40 %. Enzymatic degreasing is a better way of carrying out degreasing than the use of solvents and detergents. Lipases are much safer and less toxic to workers and the environment. Ultrafiltration (UF) can be used to treat the exhausted bath from the degreasing operation in order to recover surfactants in the permeate stream which can be recycled to the degreasing step leading to a reduction in raw material costs. Fat substances removed from the skins can be concentrated in the retentate stream and reused, after physical and chemical treatments, in the fat liquoring step with significant reduction of the wastewater treatment costs (Koltuniewicz 2010). Leather Industry, Unhairing-Liming In another approach the UF process can be combined to an enzymatic degreasing step (Fig. 1) with a continuous recycling of the permeate stream in the drum (Cassano et al. 1998). The proposed methodology permits to obtain a high removal efficiency of fatty substances from the degreasing bath and a reduction of washing cycles normally employed to remove the lipidic substances from skins and, consequently, of water consumption. Polysulfone membranes with molecular weight cutoff of 20 kDa, in spiralwound configuration, exhibited rejections toward chemical oxygen demand (COD) and fat substances higher than 97 %. References Cassano A, Drioli E, Molinari R (1998) Integration of ultrafiltration into unhairing and degreasing operations. J Soc Leather Technol Chem 82:130–135 Koltuniewicz A (2010) Integrated membrane operations in various industrial sectors. In: Drioli E, Giorno L (eds) Comprehensive membrane science and engineering. Elsevier, Kidlington, pp 109–164 1095 salt compounds with dirt (blood, excrement, earth) which are attached to the skins. The soaking-exhausted effluent-containing excrements, salts, and chemical additives are normally discharged into a water-treatment plant (Sharphouse 1983). UF membranes can be used to concentrate organic components in the feed tank of the UF plant. A clear permeate, enriched in salt compounds, could be reused in the pickling step after adjustment of the salt concentration with NaCl (Fig. 1). Preliminary treatments are necessary in order to remove the suspended materials; a sedimentation step allows to reduce the suspended solids of 90 %; then steel spring filters (200–300 mm net size) could be employed to remove large particles avoiding clogging phenomena of UF membranes (Cassano et al. 2001). References Cassano A, Molinari R, Romano M, Drioli E (2001) Treatment of aqueous effluents of the leather industry by membrane processes. A review. J Membr Sci 181:111–126 Sharphouse JH (1983) Leather technicians handbook. Leather Producers Association, Northampton Leather Industry, Soaking Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy In this operation, raw skins are exposed to water and chemicals (small quantities of imbibing substances) in order to hydrate proteins and fibers, to solubilize the denatured proteins, and to eliminate Leather Industry, Soaking, Fig. 1 Treatment of exhausted effluents of the soaking step by UF process Leather Industry, Unhairing-Liming Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy The aim of the unhairing-liming step is to remove from the raw skin all the components which are water, imbibing substances, skins purging exhausted bath UF pickling L 1096 Leather Industry, Unhairing-Liming proteic flour desulfidation desalination drying water, Ca(OH)2, Na2S skins concentrated proteic fractions exhausted bath UF Permeate (low M.W. species, sulfide) preparation of new liming baths Leather Industry, Unhairing-Liming, Fig. 1 Treatment of exhausted liming effluent by ultrafiltration not transformed into leather, such as the superficial epidermis including the hair and the subcutaneous adipose layer. The liming step introduces chemicals such as lime (Ca(OH)2) and sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) which open the fibrous structure of the skin. Consequently, exhausted effluents are highly polluted for the presence of sulfide, amines, organic matter coming from degradation of hairs and epidermis, and high concentration of alkalis. The COD of exhausted effluents ranges between 20,000 and 40,000 mg/L of consumed oxygen. The UF treatment of the exhausted unhairing liquor has been one of the first membrane approaches introduced in the leather industry (Molinari 1995). It can be exploited to recover sulfide and solubilized lime together with low molecular weight proteic substances in the permeate stream in order to reuse the purified solution for the preparation of a new liming bath. High molecular weight proteic components, coming from chemical degradation of hairs and epidermis, are concentrated in the retentate stream (Fig. 1). Considering that 60–65 % of the initial sulfide remains in the exhausted liquor and 5–10 % is lost in the retentate, the quantity of sulfide that is possible to recycle with an UF system is 55–60 %. An innovating system based on the use of enzymes and small quantities of sodium sulfide (1.5 % instead of 10 %) has been proposed and tested on industrial scale. In this approach the enzymatic unhairing was combined to the continuous cross-flow UF of the bath permitting to keep constant the sulfide concentration in the unhairing bath due to its permeation through the UF membrane. The organic components (products of degradation of the keratin and of the interfibrillar proteins, fat substances, etc.) are concentrated in the retentate stream. This new approach is safer for workers and characterized by a reduced environmental impact because hairs are not dissolved and can be removed separately (Cassano et al. 1998). References Cassano A, Drioli E, Molinari R (1998) Integration of ultrafiltration into unhairing and degreasing operations. J Soc Leath Technol Chem 82:130–135 Molinari R (1995) Application of membrane separation techniques to the treatment of tanneries wastewaters. In: Caetano A, De Pinho MN, Drioli E, Muntau H (eds) Membrane technology: application to industrial wastewater treatment. Kluwer, The Netherlands, pp 101–122 Leather Processing, Chromium Recovery 1097 Leather Processing, Chromium Recovery Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy In the tannage operation tanning agents are used in order to prevent the leather from chemical and thermal degradation. The most common tanning agent is the chromium basic sulfate. It enters the pores of the skin by a diffusion process to react with the collagen carboxyl groups and to form inter- and intramolecular cross-linking which results in physical, chemical, and biological stability. The exhausted bath coming from the chromium tannage contains about 30 % of the Watar NaCl Cr 2(SO4)3 NaHCO 3 initial salt content and it is normally sent to a cleaning-up plant. Here chromium salts end up into the sludges creating serious problems for their disposal. Chromium recovery from tanning exhausted baths represents a significant economical advantage for the leather industry in terms of its reuse and for the simplification of the depolluting process of global effluents. An integrated process based on a preliminary ultrafiltration (UF) of the spent liquor followed by a nanofiltration (NF) treatment of the UF permeate has been proposed as a technically viable method for recovering chromium salts from spent tanning liquors (Cassano et al. 1996, 2007). The UF process allows a marked reduction of suspended solids and fat substances. The concentrated chromium solution obtained in the NF process can be reused for the preparation of new tanning baths. The NF permeate can be reused in the pickling step because of its high content of chlorides (Fig. 1). Skins UF Equalization tank permeate Exhausted solution CHROMIUM TANNAGE NF Water NaCl acids Skins PICKEL Leather Processing, Chromium Recovery, Fig. 1 Proposed process scheme for the chromium recovery from exhausted chromium baths L 1098 Leather Processing, Deliming-Bating References Cassano A, Drioli E, Molinari R, Bertolutti C (1996) Quality improvement of recycled chromium in the tanning operation by membrane processes. Desalination 108:193–203 Cassano A, Della Pietra L, Drioli E (2007) Integrated membrane process for the recovery of chromium salts from tannery effluents. Ind Eng Chem Res 46:6825–6830 Leather Processing, Deliming-Bating Alfredo Cassano Institute on Membrane Technology, National Research Council of Italy, ITM-CNR, Rende, Italy and from the ammonium sulfate used as chemical auxiliary. In order to reduce the nitrogen concentration in the deliming/bating exhausted bath, the replacement of ammonium salts by carbon dioxide (CO2) and the reuse of wastewater and chemicals after membrane filtration (MF or UF) of the exhausted liquor has been proposed (Gallego-Molina et al. 2013). MF or UF membranes lead to a remarkable reduction of COD and fat substances of the exhausted liquor (Cassano et al. 2001). The permeate solution can be reused for the preparation of new bating baths or as washing water (Fig. 1), providing environmental and economic benefits due to the water consumption reduction and the reduction in nitrogen and salt discharge. Cross-References The deliming step is carried out to reduce the excess of liming agents used in the previous unhairing operation by using acids and/or acidic salts. Since the pH must be slowly lowered, ammonium salts are commonly used for this purpose. In the bating operation, skins are treated with proteolytic enzymes in order to open the fibrous structure of skins, increasing their softness. Generally, deliming and bating operations are performed in the same drum. Wastewaters from these operations are characterized by high nitrogen content, coming from both the hide structure water, acids, ammonium salts/CO2, surfactants, enzymes ▶ Durability of Membrane) Membrane (Lifetime of References Cassano A, Molinari R, Romano M, Drioli E (2001) Treatment of aqueous effluents of the leather industry by membrane processes. A review. J Membr Sci 181:111–126 Gallego-Molina A, Mendoza-Roca JA, Aguado D, Galiana-Aleixandre MV (2013) Reducing pollution from the deliming–bating operation in a tannery. Wastewater reuse by microfiltration membranes. Chem Eng Res Des 91:369–376 concentrate (reject stream to management) exhausted bath MF / UF washing solution preparation of new bating baths Leather Processing, Deliming-Bating, Fig. 1 Proposed process scheme for the treatment of exhausted deliming baths Lipid Coverage of a Regenerated Cellulose Membrane: Effect on Ion Transport on RC supports was already described (Benavente et al. 2011). Impedance is an a.c. technique for determining membrane electrical resistance and capacitance by measurements performed at different frequencies (Benavente 2009). As was already indicated (Benavente et al. 2011), IS measurements for dry LL-modified membranes showed a reduction in conductivity and dielectric constant when compared with original regenerated cellulose support, estimating a thickness of 2 mm for the LL. Figure 1a shows a comparison of Z vs frequency plots for hydrated RC and lipid-layer RC/LL membranes, where differences associated with electrode-membrane interface (f <5 kHz) and bulk membrane can be observed as an indication of lipid coverage of RC support and its effect on the reduction of water (or electrolyte) adsorption by the cellulose structure. Membrane potential (Dømeb) is the electrical potential at both sides of membranes in contact with different electrolyte concentrations, and Fig. 1b shows Dømeb values vs NaCl concentrtion ratio cv/cc. Two different Dømeb-ln(cv/cv) relationships are observed depending on the concentration ratio values: (i) a Donnan-potential contribution for 0.2  cv/cc  10, which is associated with co-ion (Cl ) exclusion due to the weak membrane effective charge (Xef  – 0.009 M); Lipid Coverage of a Regenerated Cellulose Membrane: Effect on Ion Transport Juana Benavente and Virginia Romero Departamento de Fisica Aplicada I, Universidad de Malaga, Facultad de Ciencias, Malaga, Spain The modification of solid substrates and membranes using biomaterials is an attractive field of research for developing new devices such as biosensors, structured multilayers, biomembrane mimetics, biomaterial coatings for therapeutical applications, etc. (Goodsell 2004; Sackmann 1996). Particularly, lipid-layer deposition on membrane supports might improve their biocompatibility, but it might also affect membrane transport parameters and, consequently, its functionality. Changes in electrical and transport parameters for a hydrophilic regenerated cellulose membrane (RC sample) as a result of lipid surface deposition (RC/LL sample) were studied by measuring impedance spectroscopy (IS) and membrane potential. Lipid-layer (glyceryl tristearate as main lipid with L-a-phosphatidylcholine and sodium taurocholate as surfactants) deposition a 104 1099 b 0 Z (W) bulk membrane 2 10 101 100 101 DFmeb (mv) 103 −10 −20 102 103 104 f(Hz) 105 106 −2 −1 0 In(Cv/Cf) 1 2 Lipid Coverage of a Regenerated Cellulose Membrane: Effect on Ion Transport, Fig. 1 (a) Impedance plot. (b) Membrane potential dependence on NaCl concentration ratio. RC (□), RC/LL (■), and FTC (D) L 1100 (ii) when 2> cv/cc >10, the higher contribution seems to correspond to the diffusion potentials as a result of the different transport of counterions (t+) and co-ions (t ) in the membrane. Lipid layer does not seem to affect membrane fixed charge, according to the similar Dømeb values obtained with RC and RC/LL membranes for the Donnanpotential branch (i), but differences in ion transport number should exist due to their different diffusion-potential contribution (<t+RC > = 0.74, <t+RC/LL > = 0.69) (ii). For comparison, Dømbr values for tomato fruit cutin (FTC), a membrane with lipids as major component (HerediaGuerrero et al. 2012), are also drawn in Fig. 1b, and its comparison with RC/LL results indicates lower fixed charge (XfFTC  – 510–4M) but rather similar transport parameters (<t+FTC > = 0.68) supporting the reliability of RC/LL values. These results show small changes in transport parameters associated with LL deposition and open the scope to study natural membranes. References Benavente J (2009) Electrical characterization of membranes. In: C. G€ uell, M. Ferrando, F. López (eds), Monitoring and visualizing membrane-based process. ISBN: 978-3-527-32006-6. Wiley-VCH Benavente J, Vázquez MI, Hierrezuelo J, Rico R, LópezRomero JM, López-Ramirez R (2010) Modification of regenerated cellulose membrane with lipid nanoparticles and layers. Nanoparticle preparation, morphological and physicochemical characterization of nanoparticles and modified membranes. J Membr Sci 355:45–52 Benavente J, Vázquez MI, Hierrezuelo J, López-Romero JM (2011) Physicochemical and transport parameters for a lipid coated regenerated cellulose membrane, Vacuum, 85:1067–1070 Goodsell DS (2004) Bionanotechnology. Wiley-Liss, New Jersey Heredia-Guerrero JA, Lara R, Dominguez E, Heredia A, Benavente J, Benitez JJ (2012) Chemical-physical characterisation isolated plant cuticles subjected to low-dose g-irradiation. Chem Phys Lipids 165:803–808 Modification of regenerated cellulose membrane with lipid nanoparticles and layers. Nanoparticle preparation, morphological and physicochemical characterization of nanoparticles and modified membranes. J Membr Sci 355:45–52 Sackmann S (1996) Supported membranes: Scientific & Practical Applications. Science 271:43–48 Lipid Monolayer/Bilayer Lipid Monolayer/Bilayer ▶ Amphiphilic Membrane Lipids/Phospholipids ▶ Amphiphilic Molecules Liquid Chromatography: Organic Carbon Detection (LC-OCD) Loreen O. Villacorte FMC Technologies, Separation Innovation and Research Center, Arnhem, The Netherlands Liquid chromatography – organic carbon detection (LC-OCD) is an analytical technique for identification and quantification of natural organic matter (NOM) constituents in aquatic environments and water-soluble synthetic organic matter in technical waters. This technique has several specific applications including NOM investigation in drinking water, wastewater, and marine waters and quality control monitoring of ultrapure water used in power plants and the semiconductor industry (Huber and Frimmel 1994; Huber et al. 2011). It is widely applied in membranebased water treatment to characterize the different NOM constituents in the source waters (e.g., Kennedy et al. 2005; Amy et al. 2011; Villacorte et al. 2012), to assess the organic removal efficiency of pretreatment and membrane filtration processes (e.g., Frimmel et al. 2004; Villacorte et al. 2009, 2010; Huang et al. 2011; Zheng et al. 2010), and to identify the NOM constituents that cause fouling in MF/UF and NF/RO systems (e.g., Huber 1998; Henderson et al. 2011; Kennedy et al. 2008; Jiang et al. 2010; Batsch et al. 2005; Zheng et al. 2009). The principle behind NOM fractionation by LC-OCD is based on three separation processes, namely, size exclusion, ion interaction, and Liquid Chromatography: Organic Carbon Detection (LC-OCD) hydrophobic interaction. Since NOM constituents are highly heterogeneous in terms of size and majority of which are hydrophilic and weakly acidic, size exclusion is considered as the dominant mechanism of separation (DOC-Labor 2006). Size exclusion chromatography (SEC) is Liquid Chromatography: Organic Carbon Detection (LC-OCD), Table 1 Characteristics of different constituents of NOM identifiable by LC-OCD (www.doc-labor.de; Huber et al. 2011; Batsch et al. 2005) NOM fraction Biopolymers Typical size (Da) >20,000 Aquatic humics Building blocks LMW neutrals 1000 LMW acids <350 300–450 <350 Typical composition Polysaccharides, proteins, amino sugars, polypeptides, TEPs, EPS Humic and fulvic acids Weathering and oxidation products of humics Mono-oligosaccharides, alcohols, aldehydes, ketones, amino acids All monoprotic organic acids 1101 based on steric interactions or physical sieving where the difference in speed of diffusion for smaller and larger molecules is used to identify the different NOM fractions in the mobile phase (e.g., buffered water sample). The stationary phase is a packing of porous beads which allows smaller molecules to diffuse into the bead interior while preventing the larger molecules to diffuse through. As a consequence, larger molecules have less volume to traverse and travel faster through the chromatogram column (shorter elution time) than smaller molecules. The modern LC-OCD technology is mainly attributed to the works of Stefan Huber in the early 1990s when he successfully improved the sensitivity of the LC/DOC (predecessor of LC-OCD) developed earlier at the Engler-Bunte Institute in Karlsruhe, Germany (http://www.doclabor.de/). The current LC-OCD system has an online organic carbon detector (OCD), UV detector (UVD), and organic nitrogen detector (OND) to continuously measure the relative signal response of organic carbon, UV, and organic nitrogen, respectively, at different retention 12 Building Blocks Humics OCD: organic carbon detection UVD: UV detection at l=254 nm Acids and OND: organic nitrogen detection LMW Humics rel. Signal Response 10 8 Biopolymers LMW-Neutrals 6 OCD 4 Inorganic Colloids 2 UVD Nitrate OND 0 20 30 60 40 50 Retention Time in Minutes 70 80 Liquid Chromatography: Organic Carbon Detection (LC-OCD), Fig. 1 Typical LC-OCD chromatogram of NOM in surface water (DOC-Labor 2006) L 1102 Liquid Chromatography: Organic Carbon Detection (LC-OCD) times. In principle, the analysis technique is as follows: (1) injection of buffered particle-free water sample to a chromatographic column to separate fractions of NOM, (2) nondestructive UV detection at 254 nm wavelength, (3) organic carbon detection based on high-sensitivity TOC analysis, and (4) simultaneous detection of organic nitrogen in bypassed samples after the UV detector (see detailed specifications by Huber et al. 2011). The chromatogram data generated by the three detectors are processed using a customized software program (ChromCALC, DOC-Labor, Karlsruhe) to calculate organic carbon concentrations of biopolymers, humic substances, building blocks, low molecular weight (LMW) acids, and neutrals fractions of NOM based on area integration of the fractional peaks. The lower limit of detection of this technique was reported to be in the low-ppb range for individual fractions (Huber and Frimmel 1991). The typical size ranges and chromatograms of the different NOM fractions detectable by LC-OCD are shown in Table 1 and Fig. 1, respectively. Cross-References ▶ Extracellular Polymeric Substance (EPS) ▶ Natural Organic Matter (NOM) ▶ Transparent Exopolymer Particle References Amy GL, Salinas-Rodriguez SG, Kennedy MD, Schippers JC, Rapenne S, Remize P-J, Barbe C, Manes CLDO, West NJ, Lebaron P, Kooij DVD, Veenendaal H, Schaule G, Petrowski K, Huber S, Sim LN, Ye Y, Chen V, Fane AG (2011) Water quality assessment tools. In: Drioli E, Criscuoli A, Macedonio F (eds) Membrane-based desalination – an integrated approach (MEDINA). IWA Publishing, New York, pp 3–32 Batsch A, Tyszler D, Br€ ugger A, Panglisch S, Thomas M (2005) Foulant analysis of modified and unmodified membranes for water and wastewater treatment with LC-OCD. Desalination 178:63–72 DOC-Labor (2006) LC-OCD – Liquid chromatography Organic Carbon Detection. Information Brochure 1/2006 Frimmel FH, Saravia F, Gorenflo A (2004) NOM removal from different raw waters by membrane filtration. Water Sci Technol Water Supply 4:165–174 Henderson RK, Subhi N, Antony A, Khan SJ, Murphy KR, Leslie GL, Chen V, Stuetz RM, Le-Clech P (2011) Evaluation of effluent organic matter fouling in ultrafiltration treatment using advanced organic characterisation techniques. J Membr Sci 382:50–59 Huang G, Meng F, Zheng X, Wang Y, Wang Z, Liu H, Jekel M (2011) Biodegradation behavior of natural organic matter (NOM) in a biological aerated filter (BAF) as a pretreatment for ultrafiltration (UF) of river water. Appl Microbiol Biotechnol 90:1795–1803 Huber SA (1998) Evidence for membrane fouling by specific TOC constituents. Desalination 119:229–234 Huber SA, Frimmel FH (1991) Flow injection analysis for organic and inorganic carbon in the low-ppb range. Anal Chem 63:2122–2130 Huber SA, Frimmel FH (1994) Direct gel chromatographic characterization and quantification of marine dissolved organic carbon using high-sensitivity DOC detection. Environ Sci Technol 28:1194–1197 Huber SA, Balz A, Abert M, Pronk W (2011) Characterisation of aquatic humic and non-humic matter with size-exclusion chromatography – organic carbon detection – organic nitrogen detection (LC-OCD-OND). Water Res 45:879–885 Jiang T, Kennedy MD, DeSchepper V, Nam S-N, Nopens I, Vanrolleghem PA, Amy G (2010) Characterization of soluble microbial products and their fouling impacts in membrane bioreactors. Environ Sci Technol 44:6642–6648 Kennedy MD, Chun HK, Yangali-Quintanilla VA, Heijman BGJ, Schippers JC (2005) Natural organic matter (NOM) fouling of ultrafiltration membranes: fractionation of NOM in surface water and characterisation by LC-OCD. Desalination 178:73–83 Kennedy MD, Kamanyi J, Heijman BGJ, Amy G (2008) Colloidal organic matter fouling of UF membranes: role of NOM composition %26 size. Desalination 220:200–213 Villacorte LO, Kennedy MD, Amy G, Schippers JC (2009) The fate of transparent exopolymer particles (TEP) in integrated membrane systems: removal through pretreatment processes and deposition on reverse osmosis membranes. Water Res 43:5039–5052 Villacorte LO, Schurer R, Kennedy MD, Amy G, Schippers JC (2010) The fate of transparent exopolymer particles in integrated membrane systems: a pilot plant study in Zeeland, The Netherlands. Desalination Water Treat 13:109–119 Villacorte LO, Ekowati Y, Winters H, Amy GL, Schippers JC, Kennedy MD (2012) Characterisation of transparent exopolymer particles (TEP) produced during algal bloom: a membrane treatment perspective. Desalin Water Treat. doi:10.1080/19443994.2012.699359 Zheng X, Ernst M, Jekel M (2009) Identification and quantification of major organic foulants in treated domestic wastewater affecting filterability in dead-end ultrafiltration. Water Res 43:238–244 Zheng X, Ernst M, Jekel M (2010) Pilot-scale investigation on the removal of organic foulants in secondary effluent by slow sand filtration prior to ultrafiltration. Water Res 44:3203–3213 Liquid Crystal Polymer Membranes 1103 Liquid Crystal Polymer Membranes P. C. van H. Kuringen, A. P. H. J. Schenning and D. J. Broer Department of Chemical Engineering and Chemistry, Group Functional Organic Materials and Devices (SFD), Eindhoven University of Technology, Eindhoven, The Netherlands Liquid crystals (LCs) combine properties of both liquids and crystals and can be organized in a variety of nanostructured polymer films with a monolithic structure. Therefore, polymer-based LCs are ultimately suited as membrane with an accurately controlled nanoporosity. Nanoporous a O O ( ) 1 O O ( ) O O ( ) O O O ( ) O O O-Na+ O ) ( ( ) O O 3 O O O O crosslinker O 2 O membranes that have a large surface area to volume ratio are of great current interest for their potential application in filtration, separation, ion conductivity, drug delivery, and catalysis. The small pore size in these materials (less than 1 nm) makes discrimination between molecules and ions based on size and shape possible. LCs can self-assemble in a variety of phases that have orientation order and, in some cases, positional order. For the construction of nanoporous membranes, various phases have been used. Well-known examples are hexagonal or columnar, lamellar or smectic, and cubic phases (Fig. 1). One-dimensional pores are made from LCs with either a hexagonal or a columnar phase. These phases are assumed by disk-shaped LCs: the polar regions are located at the center of the O C12H25O N+ BF4- ( )O O O ( ) O O Na+ O- b 1D 2D Liquid Crystal Polymer Membranes, Fig. 1 (a) Examples of chemical structures of the LCs used in the construction of nanoporous membranes. One columnar or hexagonal LC, two smectic or lamellar LC, and three bicontinuous cubic LC. (b) The self-assembly of these 3D materials to form nanostructured materials, with respectively one, two, or three dimensional pores. The red part represents the pore while the blue fraction is the molecular region (Adapted with permission from reference (Kato 2010). Copyright Wiley, VCH) L 1104 columns and the hydrocarbon tails form the surrounding matrix (Fig. 1-a1). If the molecules are well aligned, these one-dimensional pores are interesting for their low tortuosity. The straight pores result in a short path length through the thickness of the material. The cylindrical pores must be continuous through the membrane and uniformly aligned perpendicular to the film surface for optimum transport. Two-dimensional pores can be created by smectic LCs (Fig. 1-a2). These rod-like LCs self-assemble in lamellar-like structures where the molecules are orientated perpendicular to the layers. A lamellar structure is created with alternating layers of a two-dimensional polymer sheets and two-dimensional pores. However, these sheets do not connect to each other. To circumvent disruption of the film, crosslinkers are used to keep the layers together. To some extent the pore size of the materials can be controlled by the length of the crosslinker. A bicontinuous cubic phase is used to make nanostructured LC membranes with pores in three dimensions (Fig. 1-a3). Generally, the molecular structure of the LC differs only slightly from the LCs used for the columnar phase. However, the self-assembly is different. Now, no alignment of the pores is needed, since the pores are orientated in three dimensions. These nanostructured LC polymer networks are used for different membrane applications, such as (anisotropic) ion conductivity (Schenning et al. 2011; Kato 2010) and gas separation (Schenning et al. 2011; Gin et al. 2006). Permeation is the product of diffusion and solubility. Therefore the solubility values of the ions and gases are very important. The local organization of the nanostructured material can promote the solubility of certain species, whereas other molecules are less soluble. This results in higher permeation and selectivity of the desired molecules compared to isotropic material of the same composition. Another application is the nanofiltration of water (Schenning et al. 2011; Gin et al. 2006; Henmi et al. 2012) Molecules smaller than the pore size can pass through the membrane, while Liquid Crystal Polymer Membranes larger molecules (contaminants) are rejected. The presence of charges in the pores of the membranes enables the selective permeation (Gin et al. 2006; Henmi et al. 2012) of ions with a remarkable selectivity: for example, a membrane with pore size of approximately 0.6 nm was shown to transport more divalent sulfate ions than monovalent chloride ions (Henmi et al. 2012). Furthermore, the pore size can be tailored to control the passage of molecules, making them suitable for programmed drug release systems or the confined environment within the material can be used to enhance chemical reactions. Nanoporous LC polymer membranes can be produced with pore sizes of 1 nm and below. Unique features can be realized, but because of the length of the pores exceeding micrometers, the permeability of liquids is generally low with high pressures necessary to achieve sufficient flow across the membrane. The challenge in this field is to make thinner membrane films of a mechanically robust material that can withstand these high pressures. Research on using mesoporous supporting layers to endure the force while the LC polymer membrane determines the separation characteristics is being undertaken. References Gin DL, Lu X, Nemade PR, Pecinovsky CS, Xu Y, Zhou M (2006) Recent advances in the design of polymerizable lyotropic liquid-crystal assemblies for heterogeneous catalysis and selective separations. Adv Funct Mater 16:865–878 Henmi M, Nakatsuji K, Ichikawa T, Tomioka H, Sakamoto T, Yosho M, Kato T (2012) Self-organized liquid-crystalline nanostructured membranes for water treatment: selective permeation of ions. Adv Mater 24:2238–2241 Kato T (2010) From nanostructured liquid crystals to polymer-based electrolytes. Angew Chem Int Ed 49:7847–7848 Schenning APHJ, Gonzalez-Lemus YC, Shishmanova IK, Broer DJ (2011) Nanoporous membranes based on liquid crystalline polymers. Liq Cryst 38(11–12): 1627–1639 Liquid Membrane Separation 1105 References Liquid Entry Pressure (LEP or LEPW) Renzo Di Felice University of Genova, Genova, Italy In membrane distillation it is of paramount importance that liquid does not fill the membrane pores, in order to keep membrane efficiency to the highest possible value. To this end hydrophobic membranes are normally used. The hydrophobicity can be quantified through the so-called liquid entry pressure (LEP) parameter, defined as the pressure difference at which liquid penetrates into the membranes pores. The pressure required to force water through the structure is inversely proportional to the opening size and dependent on the polymeric properties of the membrane. A theoretical expression, based on Young-Laplace equation, enables the estimation of LEP (see, e.g., El Bourawi et al. 2006): 2gcosy DP ¼ r where g is the liquid surface tension, y the contact angle between liquid and membrane, and r is the pore radius. Given the practical difficulty of obtaining the exact value of the above physical parameters, it is not uncommon to estimate LEP experimentally, and Smolders and Franken (1989) described a detailed procedure which should be followed in this case. Basically pressure difference is gradually applied on both side of the membrane until the first drop of the liquid appears on the permeate side (more specific description is given in the suggested reference). Typical values of LEP range from tenth to tens of bars (0.1–20 bar): for example, with liquid water at ambient condition, a PTFE membrane with 95 % porosity, 25 mm thickness, and 3 mm nominal pore size has an LEP of 0.13 bar, whereas a PTFE supported membrane with 75 % porosity, 120 mm thickness, and 0.2 nominal pore size has an LEP of 4.0 bar (Kim and Harriot 1987). El Bourawi S, Ding Z, Ma R, Khayet M (2006) A framework for better understanding membrane distillation separation processes. J Membr Sci 285:4–29 Kim B-S, Harriot P (1987) Critical entry pressure for liquids in hydrophobic membranes. J Colloid Interface Sci 115:1–8 Smolders K, Franken ACM (1989) Terminology for membrane distillation. Desalination 72:249–262 Liquid Membrane Separation Vladimir S. Kislik Campus Givat Ram, Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel Liquid membrane separation combines the solvent extraction and stripping processes (re-extraction) in a single step. This entry has the objective of introducing the reader to the basic definitions of the liquid membrane field, with classification. The term liquid membrane transport includes processes incorporating liquid-liquid extraction (LLX) and membrane separation in one continuously operating device. It utilizes an extracting reagent solution, immiscible with water, stagnant or flowing between two aqueous solutions (or gases), the source or feed, and receiving or strip phases. In most cases, the source and receiving phases are aqueous, and the membrane is organic, but the reverse configuration can also be used. A polymeric or inorganic microporous support (membrane) may be used as bearer (as in SLM) or barrier (as in BLM technologies) or not used, as in ELM and layered BLM (see respective entries: SLM, ▶ Emulsion Liquid Membrane (ELM), ▶ Silver Recovery by Bulk Liquid Membrane (BLM)). The great potential for energy saving, low capital and operating cost, and the possibility to use expensive extractants, due to the small amounts of the membrane phase, make LMs an area deserving special attention. Liquid membrane systems L 1106 are being studied extensively by researchers in such fields as analytical, inorganic, and organic chemistry; chemical engineering, biotechnology, and biomedical engineering; and wastewater treatment. Research and development activities within these disciplines involve diverse applications of liquid membrane technology, such as gas separations, recovery of valued or toxic metals, removal of organic compounds, development of sensing devices, recovery of fermentation products, and some other biological systems. The general properties of liquid membrane systems have been a subject of extensive theoretical and experimental studies. Some general characteristics of LM processes are as follows: 1. Liquid membrane separation is a rate process, and the separation occurs due to a chemical potential gradient, not by equilibrium between phases. 2. LM is defined based on its function, not the material used in fabrication. Permeation is a general term for the concentration-driven membrane-based mass transport process. Differences in the permeability produce a separation between solutes at constant driving force. Because the diffusion coefficients in liquids are typically orders of magnitude higher than in polymers, a larger flux can be obtained with liquid membranes. Application of a pressure difference, an electric field, or temperature considerably intensifies the process. There are several different directions in LM separation classifications: according to module design configurations (see SLM, ▶ Emulsion Liquid Membrane (ELM), ▶ Silver Recovery by Bulk Liquid Membrane (BLM) entries), according to transport mechanisms (see ▶ Transport Mechanisms with Liquid Membranes), according to applications, according to carrier type, and according to membrane support type. Below, these types of classifications are described and discussed briefly. According to configuration definition, three groups of liquid membranes are usually Liquid Membrane Separation considered (see Fig. 1): bulk (BLM), supported or immobilized (SLM or ILM), and emulsion (ELM) liquid membrane transport. Some authors add to these definitions polymeric inclusion membranes, gel membranes, and dual-module hollow-fiber membranes, but, to my opinion, the first two types are the modifications of the SLM, and the third is the modification of BLM. According to the transport mechanisms, the LM techniques may be divided into simple transport, facilitated or carrier-mediated transport, coupled counter- or cotransport, and active transport. According to applications, the LM techniques may be divided into (1) metal separationconcentration, (2) biotechnological product recovery-separation, (3) pharmaceutical product recovery-separation, (4) organic compound separation and organic pollutant recovery from wastewaters, (5) gas separations, (6) fermentation or enzymatic conversion-recovery-separation (bioreactors), (7) analytical applications, and (8) wastewater treatment including biodegradationseparation techniques. Classification according to carrier type is as follows: (1) water-immiscible, organic carriers, (2) water-soluble polymers, (3) electrostatic, ion-exchange carriers, and (4) neutral, but polarizable carriers. Classification according to membrane support type is as follows: (1) neutral hydrophobic, hydrophilic membranes, (2) charged (ion-exchange) membranes, (3) flat sheet, spiral module membranes, (4) hollow-fiber membranes, and (5) capillary hollow-fiber membranes. Module design configurations are used as a rule as basic classification. Practically, there are a lot of opportunities for liquid membrane separation processes in many areas of industry. The most interesting developments for industrial membrane technologies are related to the possibility of integrating various membrane operations in the same industrial cycle, with overall important benefits in terms of product quality and plant compactness. Liquid Permeability Liquid Membrane Separation, Fig. 1 Three configurations of liquid membrane systems: bulk (BLM), supported (immobilized) (SLM or ILM), and emulsion (ELM). F is the source or feed phase, E is the liquid membrane, and R is the receiving phase 1107 BLM F E R Porous Support Porous Support SLM E F R Porous Support ELM E R L F Liquid Permeability Alexey Volkov A.V. Topchiev Institute of Petrochemical Synthesis Russian Academy of Sciences (TIPS RAS), Moscow, Russia Liquid permeability is a liquid flux normalized by driving force – applied pressure difference across the membrane. Liquid permeability can be expressed in volumetric or gravimetric units – [l/(m2
h
bar)] or [kg/(m2
h
bar)], respectively. This parameter is used to characterize the membrane productivity and passage of pure solvent or solution, in liquid separation process such F as micro-, ultra-, and nanofiltration, reverse and forward osmosis, or hybrid processes like membranes for fuel cell. For commercial membranes liquid permeability is usually given by manufacturers along with value of molecular weight cutoff (MWCO); the last one is characterized the ability of the membrane to reject the solutes with certain molecular weight. Since it is already normalized by driving force of the process, liquid permeability shall be most likely constant value for specific membrane in certain range of operated pressures at constant feed composition and temperature. Due to its uniformity, this parameter allows to compare performance of diverse number of membranes between each other, tested in accordance with different filtration protocols. 1108 In some cases, the liquid permeability can be a function of transmembrane pressure, especially if the membrane material of top layer has a noticeable affinity to the solvent like for organic solvent nanofiltration. Then, increase of pressure difference across the membrane could lead to partial compaction of swollen polymer matrix resulting in some decline of liquid permeability (Volkov et al. 2008). This is typically a reversible effect, and the membrane recovers its transport properties, while the pressure is reduced again. However, if it is accompanied by collapsing of the membrane porous structure or transformation of membrane morphology (e.g., as a result of chemical cleaning), the change in liquid permeability is irreversible. In a case of membrane fouling, there could be a combination of reversible and irreversible decline in liquid permeability, and partial recovery of membrane performance is possible after regeneration stage (Drioli and Giorno 2010). Liquid permeability can be determined from filtration experiments in dead-end or cross-flow regimes. Ideally, no difference between two regimes shall be expected for filtration of pure solvents or dilute solutions of solutes with no specific interaction with membrane material. Meanwhile, it is preferable to carry out the filtration test in cross-flow membrane cell with high linear velocity in order to minimize concentration polarization effect or membrane fouling during the filtration of real mixtures (e.g., ground or wastewater). References Drioli E, Giorno L (2010) Comprehensive membrane science and engineering, vol 1. Elsevier, Kidlington Volkov AV, Korneeva GA, Tereshchenko GF (2008) Organic solvent nanofiltration: prospects and applications. Russ Chem Rev 77:983–993 Liquid-Liquid Membrane Extraction ▶ Membrane Based Solvent Extraction Liquid-Liquid Membrane Extraction Lotus Effect Wolfgang M. Sigmund1 and Shu-Hau Hsu2 1 Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA 2 Department of Energy Engineering, Hanyang University, Seoul, Republic of Korea Lotus leaf (Nelumbo nucifera) has become the epitome of natural superhydrophobic surfaces and has long been considered as a sacred symbol of purity for thousand years in oriental culture due to its impressive self-cleaning feature, where leaves remain unsmudged even being immersed into muddy water. Water contact angle on lotus leaf is reported above 160 with few degrees of roll-off angle. Therefore, lotus effect is sometimes a synonym for superhydrophobicity or self-cleaning nowadays. Although the effect has long been noticed for several generations, a systematically detailed investigation was not carried out until 1997 where more than 200 water-repellent plants were studied via scanning electron microscopy (Neinhuis and Barthlott 1997). The study reveals the secret of lotus leaf, which, not surprisingly, attributes to its combination of surface roughness and chemical substances. Hydrophobicity and self-cleaning of lotus leaf are believed as a mechanism to resist harmful microorganism bounding to the leaf surface, since water is usually required for the germination. The lotus leaf is covered by small protrusions (Fig. 1a) called papillae with their average diameter and height about 10 mm. The papillae are further covered by an additional layer of epicuticular waxes, generated from epidermal cells (Fig. 1b). These wax crystals are presented in submicron size and in crystalline tubules with water contact angles of about 95–110 , which is considered hydrophobic. The epicuticular waxes play a practically important role as they are not only to provide hydrophobicity but to generate an additional roughness in a smaller length of scale other than micronsized bumps. The absence of wax crystals, i.e., dropping hot water onto the leaf, will totally eliminate the superhydrophobicity (Liu et al. 2009). The Low Fouling Membranes 1109 Lotus Effect, Fig. 1 SEM micrographs of lotus leaf showing its relatively rough surface covered by small micron-sized protrusions (a) and submicron-sized wax crystals (b) (Hsu 2010) kind of hierarchical roughness on superhydrophobic surfaces seems to play a crucial role, but the detailed mechanism is not yet completely clear. A general benefit suggested is to repel both macro- and microscope water droplets (Nosonovsky and Bhushan 2007). Surfaces with only one scale of roughness repelled macroscopic droplets fairly well, while the condensation may easily form microscopic droplets between the grooves of the surface structure. References Hsu SH (2010) Biologically inspired hairy surfaces for liquid repellency. Doctoral dissertation, University of Florida Liu Y, Chen X, Xin JH (2009) Can superhydrophobic surfaces repel hot water? J Mater Chem 19:5602–5611 Neinhuis C, Barthlott W (1997) Characterization and distribution of water-repellent, self-cleaning plant surfaces. Ann Bot 79:667–677 Nosonovsky M, Bhushan B (2007) Multiscale friction mechanisms and hierarchical surfaces in nano- and bio-tribology. Mater Sci Eng R 58:162–193 Low Fouling Membranes Bijay P. Tripathi Department of Nanostructured Materials, Leibniz Institute of Polymer Research Dresden, Dresden, Germany Membrane fouling – a common hindrance to the advancement of water treatment and separation membrane technologies, including microfiltration, ultrafiltration, nanofiltration, and osmosis processes – diminishes process productivity, raises operating costs, and shortens membrane life span. Fouling is the deposition of retained particles, colloids, macromolecules, salts, etc., at the membrane surface or inside the pore, and at the pore walls. Fouling reduces the membrane flux either temporarily or permanently. The decrease of permeate flux or irreversible membrane fouling is recognized as the main problem in the application of membrane filtration technologies. Several types of membrane fouling have been introduced including inorganic fouling or scaling, colloidal fouling, organic fouling, and biofouling. A schematic representation is given in Fig. 1. Among them, the formation of biofilms on the membrane surfaces or membrane biofouling has been regarded as the most serious problem. The biofouling or biofilm formation starts with the adsorption of proteins and humic substances on membrane surfaces which serves as nutrient for microorganisms (Banerjee et al. 2011; Lejars et al. 2012). The two major approaches to combat surface fouling are based on either preventing foulants from attaching or degrading them. It is generally accepted that an increase in hydrophilicity offers better fouling resistance because protein and many other foulants are hydrophobic in nature (Rana and Matsuura 2010). The high hydrophilicity leads to a high surface hydration which is generally considered L 1110 Low Fouling Membranes Organic Fouling Precipitate Fouling Colloidal Fouling Membrane fouling Biofouling Low Fouling Membranes, Fig. 1 Schematic representation of different types of fouling the key to nonspecific protein adsorption resistance, organic fouling, microorganisms attachment, etc., since a tightly bound water layer forms a physical and energetic barrier to prevent the adsorption to the surface. While proteinresistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection, it is highly desirable to design coatings that are bactericidal. More recently, hydrophilic coatings using 3,4-dihydroxyphenylalanine (DOPA) and dopamine have been used to modify the surface of microporous polyethylene (PE), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE), polysulfone, etc. membranes. The strong adhesive properties of these compounds formed films that attached well to the hydrophobic membranes and decreased the contact angle from 50 to 30 . PEG-modified polydopamine coatings showed additional resistance to protein and bacterial adhesion. Compared with the traditional hydrophilic antifouling membrane surfaces, amphiphilic membrane surfaces engineered by the “forced surface segregation” method were demonstrated to exhibit ultralow membrane fouling. The amphiphilic surfaces bearing mixed brush architecture comprised of both hydrophilic blocks and low surface energy blocks are also suggested to be potential antifouling agents. Hydrophilic blocks generated fouling-resistant hydration layers, whereas low surface energy blocks which formed amounts of nonadhesive microdomains played a major role in repulsing the foulants away from the surfaces. Surface modification with zwitterionic molecules and polymers is believed to be the most effective method to counter all types of fouling (Tripathi et al. 2013). Zwitterionic surfaces and LTA Zeolite Membranes membranes can be obtained by reacting different sultones with amine group containing polymers such as chitosan, polystyrene-poly-4-vinylpyridine block copolymer, etc. Incorporation of nanoparticles into polymeric filtration membranes such as silica, Al2O3, and TiO2 etc. also reported to enhance the antifouling performance of the membranes because the presence of hydrophilic nanoparticles in the polymer matrix enhances its overall hydrophilic behavior. Nano-sized TiO2 has received significant interest for its high hydrophilicity, chemical stability, and antibacterial properties (Mansouri et al. 2010). In addition, anatase TiO2 could serve as a photocatalyst to degrade pollutants during wastewater treatment while having an antimicrobial effect in the presence of UV. References Banerjee I, Pangule RC, Kane RS (2011) Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms. Adv Mater 23:690–718 Lejars M, Margaillan A, Bressy C (2012) Fouling release coatings: a nontoxic alternative to biocidal antifouling coatings. Chem Rev 112:4347–4390 Mansouri J, Harrisson S, Chen V (2010) Strategies for controlling biofouling in membrane filtration systems: challenges and opportunities. J Mater Chem 20:4567–4586 Rana D, Matsuura T (2010) Surface modifications for antifouling membranes. Chem Rev 110:2448–2471 Tripathi BP, Dubey NC, Choudhury S, Simon F, Stamm M (2013) Antifouling and antibiofouling pH responsive block copolymer based membranes by selective surface modification. J Mater Chem B 1:3397–3409 1111 LTA Zeolite Membranes Yanshuo Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, CAS, Dalian, China LTA zeolite membrane is one of the most wellstudied zeolite membranes for the separation of light gases and dewatering of organics. LTA (Linde type A) zeolite has a three-dimensional pore structure, consisting of secondary building units (SBUs) 4, 6, 8, and 4-4 (Meier et al.). An example material is NaA zeolite (Linde type A sodium form) with chemical formula of Na12Al12Si12O48
27H2O. The unit cell of NaA zeolite is cubic (a = 24.61 Å) with Fm-3c symmetry. The pore diameter of NaA zeolite is defined by an eight-member oxygen ring with size around 4.3 Å. Generally, LTA zeolite membranes exist in the form of composite membranes, for which porous ceramic supports, typically alumina tubes, are usually used as substrates. The effective LTA zeolite separating layer is usually in the thickness of several microns (Fig. 1). The most used strategies for the synthesis of LTA zeolite membranes are in situ synthesis and secondary (seeded) growth. Microwave techniques combining with these strategies have been applied for the synthesis of LTA zeolite membranes (Li et al. 2008). As compared with conventional hydrothermal synthesis, microwave synthesis of zeolite membranes has the LTA Zeolite Membranes, Fig. 1 (a) Framework structure of LTA zeolite, (b) typical SEM image of a NaA zeolite single crystal, (c, d) typical SEM image of a LTA zeolite membrane L 1112 advantages of shorter synthesis time, better membrane performance, and easier to scale up. LTA zeolite membrane has been extensively studied for the separation of light gas mixtures, e.g., H2/CH4, O2/N2, and n-C4H10/i-C4H10 gas pairs. The observed separation factors beyond the selectivities predicted from Knudsen diffusion are attributed to the so-called molecular sieving function. Another important application of LTA (particularly NaA) zeolite membranes is for removing water from various organics via pervaporation (PV) or vapor permeation (VP), thanks to its ultramicroporous channel structure and its hydrophilic nature. Nowadays, VP dewatering technology based on NaA zeolite membranes has been widely used in the industries of chemistry, bioenergy, electronics, pharmaceutics, etc. Compared with azeotropic distillation, pressure swing adsorption (PSA), and polymeric membranes, zeolite membrane can remarkably reduce the energy consumption for dewatering of organics (Van hoof et al. 2004). References Li YS (2008) Microwave synthesis of zeolite membranes: a review. J Membr Sci 316:3–17 Meier WM, Olson DH, Baerlocher C, Atlas of zeolite structure types, ISBN-13: 978-0444100153, Excerpta Medica Van Hoof V et al (2004) Economic comparison between azeotropic distillation and different hybrid systems combining distillation with pervaporation for the dehydration of isopropanol. Sep Purif Technol 37:33–49 LTA Zeolite Membranes in Pervaporation Yanshuo Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, CAS, Dalian, China LTA Zeolite Membrane in Pervaporation. Pervaporation (PV) or vapor permeation (VP) is a membrane-based separation process which LTA Zeolite Membranes in Pervaporation LTA Zeolite Membranes in Pervaporation, Table 1 Typical PV/VP performances of LTA zeolite membrane for dewatering organics Feed solution (10 wt.% of water) Water/methanol Water/ethanol Water/ethanol Water/n-propanol Water/i-propanol Water/ethyl acetate Water/acetone Water/ipropylamine Temperature [ C] Water flux (kg/m2h) Separation factor 65 (PV) 65 (PV) 120 (VP) 110 (VP) 65 (PV) 65 (PV) 0.6 1.0 3.1 2.5 1.8 1.2 116 10,000 10,000 10,000 10,000 10,000 50 (PV) 105 (VP) 0.9 3.2 10,000 10,000 shows a high efficiency for the separation of azeotropes and close-boiling mixtures (Huang 1991). In general, zeolites with low Si/Al ratio can be adopted to produce hydrophilic pervaporative membranes for dewatering of organics, as exemplified by LTA, FAU, SOD, and T-type zeolites (Bowen et al. 2004). Among those, LTA zeolite membranes exhibit the highest water to alcohol selectivity up to present, owing to its lowest Si/Al ratio and proper pore size (0.4 nm) that can block organic solvent molecules bulkier than water. LTA zeolite membranes have been widely used for dewatering various organics, including alcohols, aldehydes, ketones, ethers, esters, amines, and amides. Typical performances of LTA membrane are listed in Table 1. LTA zeolite membrane is the first zeolite membrane to be used in large-scale industries for the dehydration of alcohols (Morigami et al. 2001). Nowadays, commercial LTA zeolite membranes (in NaA form) can be bought from the Japanese company, the Nano-Research Institute Inc. (XNRI), a 100 % subsidiary of Mitsui & Co., the European alliance between Smart (UK) and Inocermic, and most recently the Chinese company, HST Co. Ltd., located at Dalian. Compared with azeotropic distillation and pressure swing adsorption (PSA), LTA zeolite membrane can remarkably reduce the energy consumption for dewatering of organics. Taking the production of anhydrous ethanol as an example, LTA zeolite membrane-based VP process can LTA Zeolite Membranes in Pervaporation reduce the consumption of steam by 40 % and cooling water by 30 % compared with PSA, respectively. 1113 Huang RYM (1991) Pervaporation membrane separation processes, Elsevier. ISBN 0444882278 Morigami Y, Kondo M, Abe J, Kita H, Okamoto K (2001) The first large-scale pervaporation plant using tubulartype module with zeolite NaA membrane. Sep Purif Tech 25:251–260 References Bowen TC, Noble RD, Falconer JL (2004) Fundamentals and applications of pervaporation through zeolite membranes. J Membr Sci 245:1–33 L