Polymers

1082 KiB

Open AccessArticle

Loading of Two Related Metal-Organic Frameworks (MOFs), [Cu₂(bdc)₂(dabco)] and [Cu₂(ndc)₂(dabco)], with Ferrocene

by Romain Heck, Osama Shekhah, Olexandra Zybaylo, Peter G. Weidler, Frank Friedrich, Robert Maul, Wolfgang Wenzel and Christof Wöll

Polymers 2011, 3(3), 1565-1574; https://doi.org/10.3390/polym3031565 - 21 Sep 2011

Cited by 24 | Viewed by 11931

Abstract

We have studied the loading of two related, similar porous metal-organic frameworks (MOFs) [Cu₂(bdc)₂(dabco)] (1), and [Cu₂(ndc)₂(dabco)] (2) with ferrocene by exposing bulk powder samples to the corresponding vapor. On the [...] Read more.

We have studied the loading of two related, similar porous metal-organic frameworks (MOFs) [Cu₂(bdc)₂(dabco)] (1), and [Cu₂(ndc)₂(dabco)] (2) with ferrocene by exposing bulk powder samples to the corresponding vapor. On the basis of powder X-ray diffraction data and molecular dynamics (MD) calculations we propose that each pore can store one ferrocene molecule. Despite the rather pronounced similarity of the two MOFs a quite different behavior is observed, for 1 loading with ferrocene leads to an anisotropic 1% contraction, whereas for 2 no deformation is observed. Mössbauer spectroscopy studies reveal that the Fe oxidation level remains unchanged during the process. Time dependent studies reveal that the diffusion constant governing the loading from the gas-phase for 1 is approximately three times larger than the value for 2. Full article

(This article belongs to the Special Issue Coordination Polymers)

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Monitoring with PXRD of the loading of ferrocene inside Cu(bdc)(dabco)1/2 (1) and Cu(ndc)(dabco)1/2 (top) (2) and compared to the theoretical calculations for both types of MOFs after loading with ferrocene (bottom). Full article ">
Geometry of [Cu2(bdc)2(dabco)] (1) after the embedding of one molecule of ferrocene per unit cell, as obtained from MD-simulations. The grey surface indicates the free space in the unit cell of the empty MOF before the loading process. White: hydrogen, teal: carbon, red: oxygen, purple: nitrogen, teal: copper, green: Ferrocene. Full article ">
SEM pictures of [(η5-C5H5)2Fe] 0.08@ [Cu2(bdc)2(dabco)] (3) (left) [(η5-C5H5)2Fe] 0.04@ [Cu2(ndc)2(dabco)] (4) (right). Full article ">
Mössbauer Spectra of ferrocene embedded in [Cu2(ndc)2(dabco)]. Full article ">
Kinetics of the loading of ferrocene inside Cu(bdc)(dabco)1/2 (1) (□) and Cu(ndc)(dabco)1/2 (2) (○). The data are plotted as the natural log of intensity against time to obtain diffusion constants. Full article ">

631 KiB

Open AccessArticle

Polymeric Optical Code-Division Multiple-Access (CDMA) Encoder and Decoder Modules

by Xuejun Lu and Ray T. Chen

Polymers 2011, 3(3), 1554-1564; https://doi.org/10.3390/polym3031554 - 19 Sep 2011

Cited by 2 | Viewed by 7497

Abstract

We propose a low cost polymeric optical waveguides-based optical CDMA encoder and decoder modules. The structures of the optical CDMA encoder and decoder modules are presented. The performance of the optical CDMA encoder and decoder modules is simulated using 10-chip binary phase-shift keying [...] Read more.

We propose a low cost polymeric optical waveguides-based optical CDMA encoder and decoder modules. The structures of the optical CDMA encoder and decoder modules are presented. The performance of the optical CDMA encoder and decoder modules is simulated using 10-chip binary phase-shift keying (BPSK) coding schemes. The optical CDMA encoder and decoder modules can effectively transmit and recover optical CDMA data streams. The SNR of the received signal is analyzed and determined to be primarily from the cross correlation with other channels. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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Schematic structure of the proposed optical Code-Division Multiple-Access (CDMA) encoder. It consists of ten 10% tap couplers, optical time-delay lines, and phase-encoders. Each of the time-delay lines is designed to provide a 5 ps time-delay. The time-delayed data streams are phase-encoded by the integrated phase-encoders. The phase-encoded data streams are finally combined and sent out through the optical CDMA output waveguide. Full article ">
Schematic structure of the thermo-optic (TO) phase encoder. It consists of a polymeric waveguide with a top electrode. The top electrode and the polymeric waveguide are separated by a cladding layer. Local heating in the polymeric waveguide can be achieved by applying current through the top electrode. The local current heater increase the temperature of the polymeric waveguide and lead to refractive index change through the TO effect of the polymeric waveguide. The refractive index change will result in phase shift of the optical signals in the waveguide. Full article ">
Schematic structure of the optical CDMA decoder for one channel. It consists of optical-time lines, optical combiners, and TO phase-decoders. The TO phase decoders are the same as in the optical CDMA encoder of the same channel. The optical CDMA decoders for other channels have the same structure with their own codes for the TO phase-decoders. Full article ">
(a) original data symbol 1 0 1 1 1 0 1 0 of channel #1. The signal bits are in non-return-to-zero (NRZ) format. Each bit of the signal is 50 ps; (b) phase-coded (BPSK) data stream of channel #1 using its phase code [0 π 0 0 0 π π 0 π 0]. Full article ">
(a) original data stream 1 1 0 0 1 1 0 1 of channel #2; (b) phase-coded (BPSK) data stream of channel #2 using its phase code [0 π 0 0 π 0 0 0 0 π]. Full article ">
Received signals. It contains the both phase-encoded channel #1 and channel #2 signals plus the additive noise accumulated in the transmission. White noise with normal distribution is used as the additive noise in the simulation. The average value and the standard deviation of the normal noise are 0 and 0.5, respectively. The received signal is corrupted with interference from the other channel and the additive noise. Full article ">
(a) the original #1 symbols (reshown from <a href="#f4-polymers-03-01554" class="html-fig">Figure 4(a)</a> for better illustration); (b) decoded signal using the optical CDMA decoder with the code of [0 π 0 0 0 π π 0 π 0] for channel #1. Using edge-detection at the end of each 50-ps signal bit, the original channel #1 data stream 1 0 1 1 1 0 1 0 can be recovered. Full article ">
(a) the original #2 symbols (reshown from <a href="#f5-polymers-03-01554" class="html-fig">Figure 5(a)</a> for better illustration); (b) decoded signal using with the code of [0 π 0 0 π 0 0 0 0 π] for channel #2. The original channel #2 data stream 1 1 0 0 1 1 0 1 can be recovered using the edge-detection. Full article ">
Calculated signal to noise ratio (SNR) for different binary phase-shift keying (BPSK) code length. Full article ">

1302 KiB

Open AccessArticle

NMR Studies and Molecular Dynamic Simulation of Synthetic Dendritic Antigens

by Maria Isabel Montañez, Francisco Najera and Ezequiel Perez-Inestrosa

Polymers 2011, 3(3), 1533-1553; https://doi.org/10.3390/polym3031533 - 13 Sep 2011

Cited by 19 | Viewed by 8170

Abstract

A series of synthetic benzylpenicillinoylated dendrimers has been prepared using up to 4th generation PAMAM dendrimers. These nanoconjugates, as nanosized Dendritic Antigens, are useful in the diagnostic evaluation of drug allergy due to specific molecular recognition with the Human Immunological System (IgE). The [...] Read more.

A series of synthetic benzylpenicillinoylated dendrimers has been prepared using up to 4th generation PAMAM dendrimers. These nanoconjugates, as nanosized Dendritic Antigens, are useful in the diagnostic evaluation of drug allergy due to specific molecular recognition with the Human Immunological System (IgE). The morphology and dimensions of the conjugates coupled to the orientation of the peripheral benzylpenicillin residues in the dendrimers may play key roles in such molecular recognition processes. Herein, the characterization and conformation of these structures are studied by a detailed analysis of 1D (¹H and ¹³C NMR) and 2D NMR (¹H,¹H-NOESY) spectra. These dendrimers in explicit solvent were studied by the atomistic forcefield-based molecular dynamics. Structural properties such as shape, radius-of-gyration and distribution of the monomers will be discussed in relation to the experimental observations. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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477 KiB

Open AccessArticle

Activity and Mechanism of Antimicrobial Peptide-Mimetic Amphiphilic Polymethacrylate Derivatives

by Iva Sovadinova, Edmund F. Palermo, Michael Urban, Philomene Mpiga, Gregory A. Caputo and Kenichi Kuroda

Polymers 2011, 3(3), 1512-1532; https://doi.org/10.3390/polym3031512 - 13 Sep 2011

Cited by 82 | Viewed by 11341

Abstract

Cationic amphiphilic polymethacrylate derivatives (PMAs) have shown potential as a novel class of synthetic antimicrobials. A panel of PMAs with varied ratios of hydrophobic and cationic side chains were synthesized and tested for antimicrobial activity and mechanism of action. The PMAs are shown [...] Read more.

Cationic amphiphilic polymethacrylate derivatives (PMAs) have shown potential as a novel class of synthetic antimicrobials. A panel of PMAs with varied ratios of hydrophobic and cationic side chains were synthesized and tested for antimicrobial activity and mechanism of action. The PMAs are shown to be active against a panel of pathogenic bacteria, including a drug-resistant Staphylococcus aureus, compared to the natural antimicrobial peptide magainin which did not display any activity against the same strain. The selected PMAs with 47–63% of methyl groups in the side chains showed minimum inhibitory concentrations of ≤2–31 µg/mL, but cause only minimal harm to human red blood cells. The PMAs also exhibit rapid bactericidal kinetics. Culturing Escherichia coli in the presence of the PMAs did not exhibit any potential to develop resistance against the PMAs. The antibacterial activities of PMAs against E. coli and S. aureus were slightly reduced in the presence of physiological salts. The activity of PMAs showed bactericidal effects against E. coli and S. aureus in both exponential and stationary growth phases. These results demonstrate that PMAs are a new antimicrobial platform with no observed development of resistance in bacteria. In addition, the PMAs permeabilized the E. coli outer membrane at polymer concentrations lower than their MIC values, but they did not show any effect on the bacterial inner membrane. This indicates that mechanisms other than membrane permeabilization may be the primary factors determining their antimicrobial activity. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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Chemical structure of amphiphilic polymethacrylate derivatives (PMAs). Full article ">
Activity spectrum of PM polymer series against G-negative (open markers and dashed lines) and G-positive (closed markers and solid lines) bacteria. The minimum inhibitory concentration (MIC) values > 1,000 μg/mL are not plotted. Full article ">
Kinetics of bactericidal activity of PMAs at 2 × MIC against E. coli (A) and S. aureus (B) subcultured from exponential (red closed markers and solid lines) and stationary (blue open markers and dashed lines) phase. The MICs of PB27 are 16 μg/mL for both strains, and those of PM63 are 16 μg/mL for E. coli and 250 μg/mL for S. aureus. Each point represents the mean of values from two separated experiments (±SD). Full article ">
Susceptibility of PMAs and antibiotics to the development of resistance in E. coli. The initial MICs of the polymers PM63 and PB27, and two conventional antibiotics ciprofloxacin (CIP) and norfloxacin (NOR) are 16, 16, 0.006, and 0.063 μg/mL, respectively. The increase in the MIC of after serial passages for PM63 (solid line) and PB27 (dashes line) is shown in the expansion in the inserted figure. Full article ">
Influence of physiological salts on the antibacterial activity of PMAs and melittin against E. coli (A) and S. aureus (B). Initial MIC values against E. coli or S. aureus—PM47: 63 or 125 μg/mL, PM63: 16 or 125 μg/mL, PB27: 16 or 16 μg/mL, melittin: 13 or 6 μg/mL. Full article ">
E. coli outer membrane permeabilization by PMAs (A) and the relationship between MIC and outer membrane (OM) permeabilization (B). The polymer concentrations are 16 μg/mL except for PM63 (13 μg/mL). The polymyxin B concentration is 1.1 μg/mL. Full article ">

1891 KiB

Open AccessReview

An Excursion into the Intriguing World of Polymeric Tl(I) and Ag(I) Cyanoximates

by Nikolay Gerasimchuk

Polymers 2011, 3(3), 1475-1511; https://doi.org/10.3390/polym3031475 - 13 Sep 2011

Cited by 15 | Viewed by 9282

Abstract

The reaction of hot (~95 °C) aqueous solutions of Tl₂CO₃ with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO [...] Read more.

The reaction of hot (~95 °C) aqueous solutions of Tl₂CO₃ with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO₃ and ML (M = K⁺, Na⁺; L = anion of the monodeprotonated cyanoxime) this time at room temperature in mixed ethanol/aqueous solutions leads to sparingly soluble, colored AgL in high-yield. All synthesized monovalent Tl and Ag complexes were characterized using a variety of spectroscopic methods and X-ray analysis, which revealed the formation of primarily 2D coordination polymers of different complexity. In all cases cyanoxime mono-anions act as bridging ligands. Thallium(I) cyanoximates adopt in most cases a double-stranded motif that is originated from centrosymmetric (TlL)₂ dimers in which two Tl₂O₂ rhombs are fused into infinite “ladder-type” structure. There are very short (3.65–3.85 Å) intermetallic distances in (TlL)_n, which are close to that (3.46 Å) in metallic thallium. This opens the possibility for the electrochemical or chemical generation of mixed valence Tl(I)/Tl(III) polymers that may exhibit electrical conductivity. Synthesized silver(I) compounds demonstrate a very significant (for multiple years!) stability towards visible light. There are three areas of potential practical applications of these unusual complexes: (1) battery-less detectors of UV-radiation, (2) non electrical sensors for gases of industrial importance, (3) antimicrobial additives to light-curable acrylate polymeric glues, fillers and adhesives used during introduction of indwelling medical devices. Chemical, structural, technological and biological aspects of application of Tl(I) and Ag(I) cyanoximes-based coordination polymers are reviewed. Full article

(This article belongs to the Special Issue Coordination Polymers)

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1478 KiB

Open AccessArticle

A Molecular Antenna Coordination Polymer from Cadmium(II) and 4,4’-Bipyridine Featuring Three Distinct Polymer Strands in the Crystal

by Rüdiger W. Seidel, Richard Goddard, Bodo Zibrowius and Iris M. Oppel

Polymers 2011, 3(3), 1458-1474; https://doi.org/10.3390/polym3031458 - 5 Sep 2011

Cited by 11 | Viewed by 12304

Abstract

Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)₂(H₂O)₂}(ClO₄)₂× 2 4,4’-bipy × 4.5 H₂O]_n( [...] Read more.

Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)₂(H₂O)₂}(ClO₄)₂× 2 4,4’-bipy × 4.5 H₂O]_n(1). The Cd²⁺ ions adopt an octahedral coordination sphere and are joined into linear chains by 4,4’-bipy via two trans coordination sites. The remaining two trans sites in the equatorial plane carry terminally monodentate-bound 4,4’-bipy ligands, resulting in a molecular antenna arrangement. The two axial sites of each Cd²⁺ ion are occupied by aqua ligands. Compound 1 crystallizes in the non-centrosymmetric, monoclinic space group C2 with three similar, crystallographically independent, cationic coordination polymer strands in the unit cell, which essentially differ only in the conformations of the 4,4’-bipyridyl ligands. Consistent with the similarity of the local coordination environments of the three independent Cd atoms in the structure, ¹¹³Cd MAS NMR spectroscopy reveals a single resonance line at 89 ppm. Full article

(This article belongs to the Special Issue Coordination Polymers)

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Graphical abstract

997 KiB

Open AccessArticle

Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks

by Kyung Min Lee and Timothy J. White

Polymers 2011, 3(3), 1447-1457; https://doi.org/10.3390/polym3031447 - 2 Sep 2011

Cited by 30 | Viewed by 8816

Abstract

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work [...] Read more.

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work summarizes and contrasts the photomechanical response of glassy polydomain, monodomain, and twisted nematic azo-LCN materials to blue-green irradiation. Building from this summary, the combinatorial photomechanical response observed upon irradiation of composite cantilevers is examined. Large scale shape adaptations are realized, with novel responses that may be of potential use in future employment of these materials in actuation. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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(a) Chemical structures of monomers employed here. The approximate concentration of 2azo was 20 wt%. (b) Illustration of cantilever geometry and terminology. E is used to denote the electric field vector of the polarization of light. Full article ">
(a) Summary of photomechanical response of PD-azo-LCN to irradiation to blue-green light as a function of polarization (i—E//x (0°), ii—E 15° to x, iii—E 45° to x, iv—E 75° to x, v—E 90° to x). (b) Summary of photomechanical response of MD-azo-LCN cantilevers to blue-green light (images vi-xv). The magnitude and directionality of the bending response is dictated by light intensity and the alignment of the liquid crystalline director to the cantilever geometry. (c) Summary of photomechanical response of TN-azo-LCN cantilevers to blue-green light. In all cases, the approximately 15 μm cantilevers were exposed to 150 mW/cm2 442 nm light polarized E//x. Full article ">
Photomechanical response of a composite cantilevers composed of a MD-azo-LCN base (“a”) and an offset MD-azo-LCN tip (o-MD-azo-LCN) (“b”) observed upon irradiation to 500 and 850 mW/cm2 in the condition when (a) a > b and (b) a < b. Full article ">
Photomechanical response of a azo-PI and azo-PI composite cantilevers composed of a MD-azo-LCN base (“a”) and the glassy azo-PI material (azo-PI) (“b”) observed upon irradiation to 500 and 850 mW/cm2. (a) Azo-PI monolithic cantilever, (b) a < b, and (c) a > b. Full article ">
Photomechanical response of a TN-azo-LCN/PD-azo-LCN composite structure. When the PD-azo-LCN base is irradiation with 100 mW/cm2, optically fixable forward/reverse bending is observed. Addressing the TN-azo-LCN portion of the structure opens and closes the “mouth” of structure. See MOVIE1 in Support Information. Full article ">

1570 KiB

Open AccessArticle

Microscopic and Spectroscopic Investigation of Poly(3-hexylthiophene) Interaction with Carbon Nanotubes

by Michele Giulianini, Eric R. Waclawik, John M. Bell, Manuela Scarselli, Paola Castrucci, Maurizio De Crescenzi and Nunzio Motta

Polymers 2011, 3(3), 1433-1446; https://doi.org/10.3390/polym3031433 - 29 Aug 2011

Cited by 34 | Viewed by 8828

Abstract

The inclusion of carbon nanotubes in polymer matrix has been proposed to enhance the polymer’s physical and electrical properties. In this study, microscopic and spectroscopic techniques are used to investigate the interaction between poly(3-hexylthiophene) (P3HT) and nanotubes and the reciprocal modification of physical [...] Read more.

The inclusion of carbon nanotubes in polymer matrix has been proposed to enhance the polymer’s physical and electrical properties. In this study, microscopic and spectroscopic techniques are used to investigate the interaction between poly(3-hexylthiophene) (P3HT) and nanotubes and the reciprocal modification of physical properties. The presence of P3HT-covered nanotubes dispersed in the polymer matrix has been observed by atomic force microscopy and transmission electron microscopy. Then, the modification of P3HT optical properties due to nanotube inclusion has been evidenced with spectroscopic techniques like absorption and Raman spectroscopy. The study is completed with detailed nanoscale analysis by scanning probe techniques. The ordered self assembly of polymer adhering on the nanotube is unveiled by showing an example of helical wrapping of P3HT. Scanning tunneling spectroscopy study provides information on the electronic structure of nanotube-polymer assembly, revealing the charge transfer from P3HT to the nanotube. Full article

(This article belongs to the Special Issue Carbon Nanotubes: Synthesis, Characterization and Applications)

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Samples of poly(3-hexylthiophene) (P3HT) and double-wall carbon nanotubes (DWNTs) composites. The weight percentage content of nanotube is reported for each sample. The solvent used is dichlorobenzene (DCB), the final concentration is 20 mg/mL. Full article ">
Atomic Force Microscopy (AFM) images of P3HT film with multi-wall carbon nanotubes (MWNTs) included. (a,c,e) 2-Dimensional image showing the nanotubes buried in the polymer matrix. (b,d,f) 3-Dimensional image highlighting the nanotubes ends coming out of the polymer matrix left and the nanotubes emerging at the surface of the polymer. Full article ">
Transmission Electron Microscopy (TEM) images of P3HT/MWNTs suspended film. Darker zones, associated with thicker parts of the film, evidence the non-planar distribution of the nanotube structure. Full article ">
(a) UV-Vis spectra of P3HT-DWNTs composites. (b) UV-VRatio of the relative intensities of peaks A and C. Full article ">
(a) Raman spectra of P3HT/DWNT compounds: (b) Energy band diagram of P3HT, DWNT Ref [<a href="#b33-polymers-03-01433" class="html-bibr">33</a>] and MWNT Ref [<a href="#b34-polymers-03-01433" class="html-bibr">34</a>]. (c) Raman spectra of P3HT/MWNT compunds w/w percentage indicated. Full article ">
(a) Polymer covered nanotube imaged by UHV-STM. Scan obtained at VSAMPLE = −500 mV and I = 0.300 nA. The line of the structure is used for profile analysis. (b) 3-D image of a P3HT covered nanotube imaged by UHV-STM. (c) Corresponding 2-D image. Scan obtained at VSAMPLE = −500 mV and I = 0.300 nA. The image has been filtered with a Gaussian smooth on the Y axis and the Z colour scale has been changed to highlight the details of the polymer wrapping. Inset: Polymer wrapping generated mathematically. (d) The same wrapped nanotube pictured in a different point of the structure. Full article ">
(a) Scanning Tunneling Spectroscopy spectrum of the bare nanotube section. The agreement between the experimental result and the theoretical curve is evident and confirmed by the coincidence of the Van Hove singularities. (b) Differential conductance related to the local density of states (LDOS) of the P3HT covered part of the nanotube. The shift of the energy gap towards the highest occupied molecular orbital (HOMO) is due to a charge transfer from the polymer to the nanotube. Full article ">

612 KiB

Open AccessArticle

Consolidation of Inorganic Precipitated Silica Gel

by Hussein Sahabi and Matthias Kind

Polymers 2011, 3(3), 1423-1432; https://doi.org/10.3390/polym3031423 - 29 Aug 2011

Cited by 8 | Viewed by 8813

Abstract

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case [...] Read more.

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case of precipitated silica gels, this consolidation process depends on temperature and pH, among other parameters. It is shown that these dependencies can be characterized by oedometer measurements. Originally, the oedometer test (one-dimensional compression test) stemmed from soil mechanics. It has proven to be an interesting novel examination method for gels. Quantitative data of the time-dependent shrinkage of gel samples can be obtained. The consolidation of the gels shows a characteristic dependence on the above parameters. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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778 KiB

Open AccessArticle

Synthesis of Stimuli-responsive, Water-soluble Poly[2-(dimethylamino)ethyl methacrylate/styrene] Statistical Copolymers by Nitroxide Mediated Polymerization

by Chi Zhang and Milan Maric

Polymers 2011, 3(3), 1398-1422; https://doi.org/10.3390/polym3031398 - 26 Aug 2011

Cited by 51 | Viewed by 14067

Abstract

2-(Dimethylamino)ethyl methacrylate/styrene statistical copolymers (poly(DMAEMA-stat-styrene)) with feed compositions f_DMAEMA = 80–95 mol%, (number average molecular weights M_n = 9.5–11.2 kg mol⁻¹) were synthesized using succinimidyl ester-functionalized BlocBuilder alkoxyamine initiator at 80 °C in bulk. Polymerization [...] Read more.

2-(Dimethylamino)ethyl methacrylate/styrene statistical copolymers (poly(DMAEMA-stat-styrene)) with feed compositions f_DMAEMA = 80–95 mol%, (number average molecular weights M_n = 9.5–11.2 kg mol⁻¹) were synthesized using succinimidyl ester-functionalized BlocBuilder alkoxyamine initiator at 80 °C in bulk. Polymerization rate increased three-fold on increasing f_DMAEMA = 80 to 95 mol%. Linear M_n increases with conversion were observed up to about 50% conversion and obtained copolymers possessed monomodal, relatively narrow molecular weight distributions (polydispersity = 1.32–1.59). Copolymers with f_DMAEMA = 80 and 90 mol% were also cleanly chain-extended with DMAEMA/styrene mixtures of 95 and 90 mol% DMAEMA, respectively, confirming the livingness of the copolymers. Copolymer phase behavior in aqueous solutions was examined by dynamic light scattering and UV-Vis spectroscopy. All copolymers exhibited lower critical solution temperature (LCST)-type behavior. LCST decreased with increasing styrene content in the copolymer and with increasing solution concentration. All copolymers were completely water-soluble and temperature insensitive at pH 4 but were more hydrophobic at pH 10, particularly copolymers with f_DMAEMA = 80 and 85 mol%, which were water-insoluble. At pH 10, LCST of copolymers with f_DMAEMA = 90 and 95 mol% were more than 10 °C lower compared to their solutions in neutral, de-ionized water. Block copolymers with two statistical blocks with different DMAEMA compositions exhibited a single LCST, suggesting the block segments were not distinct enough to exhibit separate LCSTs in water. Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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Graphical abstract

312 KiB

Open AccessReview

Poly Lactic-co-Glycolic Acid (PLGA) as Biodegradable Controlled Drug Delivery Carrier

by Hirenkumar K. Makadia and Steven J. Siegel

Polymers 2011, 3(3), 1377-1397; https://doi.org/10.3390/polym3031377 - 26 Aug 2011

Cited by 3379 | Viewed by 91102

Abstract

In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties [...] Read more.

In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties and most importantly, is a FDA approved polymer. In particular, PLGA has been extensively studied for the development of devices for controlled delivery of small molecule drugs, proteins and other macromolecules in commercial use and in research. This manuscript describes the various fabrication techniques for these devices and the factors affecting their degradation and drug release. Full article

(This article belongs to the Special Issue Bioinspired Polymers)

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634 KiB

Open AccessArticle

Influence of the Hydrophobicity of Polyelectrolytes on Polyelectrolyte Complex Formation and Complex Particle Structure and Shape

by Mandy Mende, Simona Schwarz, Stefan Zschoche, Gudrun Petzold and Andreas Janke

Polymers 2011, 3(3), 1363-1376; https://doi.org/10.3390/polym3031363 - 25 Aug 2011

Cited by 13 | Viewed by 7913

Abstract

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar [...] Read more.

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar charges of the polyelectrolytes and the procedure of formation were varied. The colloidal stability of the systems and the size, shape, and structure of the PEC particles were investigated by turbidimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). Dynamic light scattering indicates that beside large PEC particle aggregates distinct smaller particles were formed by the copolymers which have the highest hydrophobicity (styrene). These findings could be proved by AFM. Fractal dimension (D), root mean square (RMS) roughness and the surface profiles of the PEC particles adsorbed on mica allow the following conclusions: the higher the hydrophobicity of the polyelectrolytes, the broader is the particle size distribution and the minor is the swelling of the PEC particles. Hence, the most compact particles are formed with the very hydrophobic copolymer. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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Structures of the polyelectrolytes: Poly(X-alt-maleimidopropyl-trimethyl-ammonium jodide) on the left side (polycation); Poly(X-alt-maleimido-ethyl (triethyl-ammonium)-sulfonate) on the right side (polyanion). Full article ">
The turbidity of PEC dispersions in dependence on the n−/n+ ratio and on time. The measurements were made after 2 h (filled symbols) and after 24 h (open symbols). a and b are the procedures of preparation: a—polycations (PC) is starting solution, b—polyanions (PA) is starting solution. The number denotes the comonomers of PC and PA, respectively. 1—ethylene, 2—isobutylene and 3—styrene. Full article ">
The z average hydrodynamic particle size dh, z av in dependence on n−/n+ ratio for stable PECs prepared on procedure a and b. (a) PC is starting solution; (b) PA is starting solution; • Eth/Eth; ⊞ Isob/Isob and ◊ Styr/Styr. Full article ">
Particle size distributions of PECs with selected n−/n+ ratios, prepared on procedure a and b. (a) PC is starting solution; (b) PA is starting. Full article ">
AFM images and some surface profiles of PECs adsorbed onto mica, (a) PECs prepared by procedure a—PC is starting solution (left Eth/Eth, mid Isob/Isob, right Styr/Styr); (b) PECs prepared by procedure b—PA is starting solution (left Eth/Eth, right Isob/Isob). All n−/n+ ratios of the PECs were 0.6. Full article ">
Schematic illustration of PECs adsorbing on the mica surface (left part of the sketch) and the situation after drying (right part) for (a) Eth/Eth PEC, (b) Isob/Isob PEC and (c) Styr/Styr PEC. Full article ">

3963 KiB

Open AccessArticle

Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene

by Gianfranco Carotenuto, Cinzia Giannini, Dritan Siliqi and Luigi Nicolais

Polymers 2011, 3(3), 1352-1362; https://doi.org/10.3390/polym3031352 - 22 Aug 2011

Cited by 6 | Viewed by 7732

Abstract

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)_x, where R is a linear aliphatic hydrocarbon group, –C_nH_2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal [...] Read more.

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)_x, where R is a linear aliphatic hydrocarbon group, –C_nH_2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR) or thioether (RSR) molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared. Full article

(This article belongs to the Special Issue Polymer-Inorganic Hybrids and Their Applications)

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Polystyrene films dyed by the surface plasmon resonance of gold nanoparticles. Depending on the average cluster size, films of different colors can be achieved (ruby-red, purple, and blue). Full article ">
TEM-micrographs of Au clusters embedded into amorphous polystyrene (the AuSC12H25/polystyrene solution was isothermally annealed for 5 min at 170 °C). Owing to the interdigitation and consequent co-crystallization of the thiol alkyl-chains coating the cluster surface, large cluster aggregates are present in this system. Full article ">
UV-Vis spectra of polystyrene-embedded gold and silver clusters. The characteristic surface plasmon absorptions of silver at 430 nm and of gold at 590 nm reveal the metal formation on a nano-sized scale. Full article ">
XRD diffractogram of gold clusters embedded in amorphous polystyrene before (A); and after (B) film dipping in pure acetone (the nanocomposite sample was obtained by isothermally annealing an AuSC12H25/polystyrene solution for 2 min at 200 °C). Full article ">
TGA-thermograms of pure thiolate compounds: (A) gold dodecyl-thiolate; and (B) lead dodecyl-thiolate. The residual weight corresponds respectively to the metal (Au) and metal sulfide (PbS) percentage in the thiolate compound. Full article ">
TEM-micrographs of different metal and metal sulfide clusters embedded into an amorphous polystyrene matrix, obtained by thermal decomposition of the corresponding metal-dodecylthiolate compounds [<a href="#b23-polymers-03-01352" class="html-bibr">23</a>–<a href="#b29-polymers-03-01352" class="html-bibr">29</a>]. Full article ">

1100 KiB

Open AccessReview

Theory-Guided Design of Organic Electro-Optic Materials and Devices

by Larry Dalton and Stephanie Benight

Polymers 2011, 3(3), 1325-1351; https://doi.org/10.3390/polym3031325 - 19 Aug 2011

Cited by 57 | Viewed by 10633

Abstract

Integrated (multi-scale) quantum and statistical mechanical theoretical methods have guided the nano-engineering of controlled intermolecular electrostatic interactions for the dramatic improvement of acentric order and thus electro-optic activity of melt-processable organic polymer and dendrimer electro-optic materials. New measurement techniques have permitted quantitative determination [...] Read more.

Integrated (multi-scale) quantum and statistical mechanical theoretical methods have guided the nano-engineering of controlled intermolecular electrostatic interactions for the dramatic improvement of acentric order and thus electro-optic activity of melt-processable organic polymer and dendrimer electro-optic materials. New measurement techniques have permitted quantitative determination of the molecular order parameters, lattice dimensionality, and nanoscale viscoelasticity properties of these new soft matter materials and have facilitated comparison of theoretically-predicted structures and thermodynamic properties with experimentally-defined structures and properties. New processing protocols have permitted further enhancement of material properties and have facilitated the fabrication of complex device structures. The integration of organic electro-optic materials into silicon photonic, plasmonic, and metamaterial device architectures has led to impressive new performance metrics for a variety of technological applications. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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1001 KiB

Open AccessArticle

Simplified Reflection Fabry-Perot Method for Determination of Electro-Optic Coefficients of Poled Polymer Thin Films

by Dong Hun Park, Jingdong Luo, Alex K.-Y. Jen and Warren N. Herman

Polymers 2011, 3(3), 1310-1324; https://doi.org/10.3390/polym3031310 - 18 Aug 2011

Cited by 11 | Viewed by 7849

Abstract

We report a simplified reflection mode Fabry-Perot interferometry method for determination of electro-optic (EO) coefficients of poled polymer thin films. Rather than fitting the detailed shape of the Fabry-Perot resonance curve, our simplification involves a technique to experimentally determine the voltage-induced shift in [...] Read more.

We report a simplified reflection mode Fabry-Perot interferometry method for determination of electro-optic (EO) coefficients of poled polymer thin films. Rather than fitting the detailed shape of the Fabry-Perot resonance curve, our simplification involves a technique to experimentally determine the voltage-induced shift in the angular position of the resonance minimum. Rigorous analysis based on optical properties of individual layers of the multilayer structure is not necessary in the data analysis. Although angle scans are involved, the experimental setup does not require a θ-2θ rotation stage and the simplified analysis is an advantage for polymer synthetic efforts requiring quick and reliable screening of new materials. Numerical and experimental results show that our proposed method can determine EO coefficients to within an error of ~8% if poled values for the refractive indices are used. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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Schematic of Fabry-Perot (FP) experimental setup (left) and representative reflectivity R and modulated reflectivity ΔR from digital voltmeter (DVM) and lock-in amplifier, respectively (right). P, HP, PD, and AC are polarizer, half wave plate, photo-detector, and voltage source, respectively. NLOP: nonlinear optical polymers Full article ">
Schematics of two Fabry-Perot structures: (a) An ideal simple three-layer structure (air/NLOP/air); (b) a practical four-layer structure (glass/TCO/NLOP/metal). Full article ">
Representative reflective curves without bias R(V = 0) and with bias R(V) to the film as a function of angle of incidence. ΔR can be measured using a lock-in amplifier and the slope ∂R/∂θ can be obtained by numerical differentiation of the experimental reflectivity curve. Full article ">
Simulated errors of r13 (blue) and r33 (red) with varying wavelengths from the calculated angular shift of the reflection minima. Full article ">
Complex index of refraction (n + iκ) of two ITOs (black: 200 nm thick Delta Technology, red: 45 nm thick Thin Film Devices) measured by ellipsometer. The inset shows a complex index of refraction of gold from [<a href="#b16-polymers-03-01310" class="html-bibr">16</a>]. Full article ">
(a) Simulated reflectivity of p-polarized light from NLO samples containing gold (black), DT (blue), or TFD (red) ITO at the wavelength of 1,550 nm. 1.73 and 1.75 were used for no and ne of NLOP, respectively and the NLOP film thickness was assumed to be 4 μm; (b) Simulated derivative of reflectivity data as a function of angle of incidence. Full article ">
Simulated Δne (solid curves) and ΔRp (dashed curves) from a sample containing a 30 nm thick gold (black) and a Delta Technology ITO (blue) under assumption of no errors in anisotropic indices of no and ne. Gray region shows ±5% error bound of Δne, directly corresponding to the error bound of an EO coefficient r33. Full article ">
Existence maps of reflection minima in the angle of incidence range 30–60° as a function of unpoled index and film thickness using 20 nm thick gold as the transparent electrode: (a) 1,550 nm with s-polarized light; (b) 1,550 nm with p-polarized light; (c) 1,320 nm with s-polarized light; and (d) 1,320 nm with p-polarized light. Black regions indicate the existence of at least one reflection minimum whereas white regions indicate the absence of reflection minima. Full article ">
Molecular structures of AJLZ53 chromophore (left) and polycarbonate (right). Full article ">

463 KiB

Open AccessArticle

Investigation of Second-Harmonic Generation and Molecular Orientation in Electrostatically Self-Assembled Thin Films

by Liangmin Zhang and Deliang Cui

Polymers 2011, 3(3), 1297-1309; https://doi.org/10.3390/polym3031297 - 18 Aug 2011

Cited by 1 | Viewed by 6322

Abstract

We report the observation and measurement of second-harmonic generation in self-assembled ultra thin film nonlinear optical materials using a femtosecond high repetition rate laser system. Second-harmonic intensity, as a function of the incident angle in these films, has been measured using incident p-polarized [...] Read more.

We report the observation and measurement of second-harmonic generation in self-assembled ultra thin film nonlinear optical materials using a femtosecond high repetition rate laser system. Second-harmonic intensity, as a function of the incident angle in these films, has been measured using incident p-polarized and s-polarized optical beam components. The second-order nonlinear optical susceptibilities of the thin films have also been determined. Using a curve fitting method and a crystal reference material, we have obtained second-order susceptibilities c₃₃₃ = 6.17 ± 0.18 pm/V and c₃₁₁ = 0.68 ± 0.02 pm/V at a fundamental wavelength of 1,200 nm. Based on linear molecular model approximation, we have also used the fitted data to investigate the average orientation distribution of the chromophore dipoles in the self-assembled film. The result indicates that the average tilt angle of the chromophore dipoles away from the substrate normal line is 25.2° ± 0.8°. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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784 KiB

Open AccessArticle

Activity and Export of Engineered Nisin-(1-22) Analogs

by Annechien Plat, Anneke Kuipers, Jacobien G. de Lange, Gert N. Moll and Rick Rink

Polymers 2011, 3(3), 1282-1296; https://doi.org/10.3390/polym3031282 - 12 Aug 2011

Cited by 13 | Viewed by 7482

Abstract

The pentacyclic peptide antibiotic nisin, produced by Lactococcus lactis is ubiquitously applied as a food preservative. We previously demonstrated that the truncated nisin-(1-22) has only 10-fold lower activity than nisin. Here we aimed at further developing this tricyclic nisin analog to reach activity [...] Read more.

The pentacyclic peptide antibiotic nisin, produced by Lactococcus lactis is ubiquitously applied as a food preservative. We previously demonstrated that the truncated nisin-(1-22) has only 10-fold lower activity than nisin. Here we aimed at further developing this tricyclic nisin analog to reach activity comparable to that of nisin. Our data demonstrate that: (1) ring A has a large mutational freedom; (2) the composition of residues 20–22 strongly affects production levels of nisin-(1-22); (3) a positively charged C-terminus of nisin-(1-22) significantly enhances its antimicrobial activity; (4) nisin-(1-22) inhibits in vitro growth of a target strain using different dynamics than nisin. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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Graphical abstract

Graphical abstract
Full article ">
Nisin A. Dha, dehydroalanine; Dhb, dehydrobutyrine; Ala-S-Ala, mesolanthionine; Abu-S-Ala, β-methyllanthionine. Full article ">
Antimicrobial activity and production of truncated nisin analogs. The three amino acids correspond to residues 4, 5 and 6 and were obtained by genetic randomization and screening for activity. Nisin- is abbreviated to n-. (a) Growth inhibition of L. lactis pNGnisT pNGnisP by colonies producing prenisin-(1-22) ring A mutants (first two rows) and colonies producing truncated prenisin analogs containing C-terminal amino acid substitutions or additions (last row), without nisin induction and (b) with nisin induction. (c) Production levels of prenisin-(1-22) ring A mutants analyzed on a tricine SDS gel. ISL is wild type prenisin-(1-22); wt denotes full length wild type prenisin. Full article ">
Antimicrobial activity and production of nisin-(1-22) mutants with substituted residues in the C-terminal tail. The three amino acids correspond to residues 20, 21, and 22. (a) Growth inhibition of L. lactis pNGnisT pNGnisP by colonies producing the truncated prenisin mutants, with nisin induction. (b) Production levels of the truncated prenisin mutants visualized on a tricine SDS gel. NMK is wild type prenisin-(1-22); wt denotes full length wild type prenisin. Full article ">
Mass spectrometry analysis of nisin-(1-22)CK digested with trypsin. The fragment with a mass of 1,400 Da (left-hand spectrum) corresponds to the first 12 residues of nisin with an extra –CK attached from the C-terminal end of another nisin peptide. Another fragment (right-hand spectrum) with a mass of 2,389 Da corresponds to residue 1 to 22 with an extra -CK attached. Full article ">
Antimicrobial activity and production of truncated (pre)nisin analogs with different C-terminal charge. (a) C-terminal positive charge enhances antimicrobial activity of truncated nisin analogs. Analogs were purified, and equal amounts were tested in a microwell dilution assay. Activities are displayed as the 50% inhibitory concentration (IC50). Apostrophe (') denotes an amidated C-terminus. The C-terminal charge of the peptides is given after the slash. An asterisk indicates significant difference (P < 0.05) between the relative antimicrobial activities, as tested by a paired t test. Error bars indicate standard deviations. (b) Production levels of the truncated prenisin analogs visualized on a tricine SDS gel. Full article ">
(a) Growth inhibition of L. lactis LL108(pORI 280) by nisin-(1-22) and nisin, alone and mixed together. (b) An enlargement of the first half of graph 6a, presented as a contour graph. Full article ">

192 KiB

Open AccessReview

Defensins: Potential Effectors in Autoimmune Rheumatic Disorders

by Stefan Vordenbäumen and Matthias Schneider

Polymers 2011, 3(3), 1268-1281; https://doi.org/10.3390/polym3031268 - 11 Aug 2011

Cited by 9 | Viewed by 7065

Abstract

Defensins are small cationic peptides with antimicrobial properties. They constitute a highly conserved innate immune defense mechanism across species. Based on the arrangement of disulfide-bonds, α- and β-defensins are distinguished in humans. Both types of defensin comprise several distinct molecules that are preferentially [...] Read more.

Defensins are small cationic peptides with antimicrobial properties. They constitute a highly conserved innate immune defense mechanism across species. Based on the arrangement of disulfide-bonds, α- and β-defensins are distinguished in humans. Both types of defensin comprise several distinct molecules that are preferentially expressed at epithelial surfaces and in blood cells. In the last decade, multiple immunomodulatory functions of defensins have been recognized, including chemotactic activity, the promotion of antigen presentation, and modulations of proinflammatory cytokine secretion. These findings suggested a role for defensins not only as a first line of defense, but also as connectors of innate and adaptive immune responses. Recently, increasingly accumulating evidence has indicated that defensins may also be involved in the pathogenesis of autoimmune rheumatic disorders such as systemic lupus erythematosus and rheumatoid arthritis. The current review summarizes the data connecting defensins to autoimmunity. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

223 KiB

Open AccessArticle

Spontaneous Vesicles Modulated by Polymers

by M. Mercedes Velázquez, Margarita Valero and Francisco Ortega

Polymers 2011, 3(3), 1255-1267; https://doi.org/10.3390/polym3031255 - 8 Aug 2011

Cited by 3 | Viewed by 6999

Abstract

Vesicles are widely used in technological applications including cosmetic products, in microencapsulation for drug delivery, as anticancer agents and in the technology of adhesives, paints and inks. The vesicle size and the surface charge are very important properties from a technological point of [...] Read more.

Vesicles are widely used in technological applications including cosmetic products, in microencapsulation for drug delivery, as anticancer agents and in the technology of adhesives, paints and inks. The vesicle size and the surface charge are very important properties from a technological point of view. Thus, the challenge in formulation is to find inexpensive stable vesicles with well-defined sizes and to modulate the surface charge of these aggregates. In this work we analyze the effect of different polymers on the structural properties of vesicles of the biodegradable surfactant sodium bis(2-ethyl-hexyl) sulfosuccinate, Aerosol OT. Using fluorescence, conductivity, electrophoretic mobility and dynamic light scattering measurements we study the effect of the polymer nature, molecular weight and polymer concentration on the stability and the vesicle size properties. Results demonstrate that it is possible to modulate both the size and the electric surface charge of spontaneous vesicles of Aerosol OT by the addition of very small percentages of poly(allylamine) and poly(maleic anhydride-alt-1-octadecen). Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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Electrical conductivity values of surfactant solutions: (triangles) sodium bis(2-ethyl-hexyl) sulfosuccinate (Aerosol OT or AOT) dissolved in 0.0001% of poly(allylamine) (PA), (circles) AOT dissolved in 0.02% PA and (squares) AOT dissolved in 0.094% poly(maleic anhydride-alt-1-octadecen) (PMAO). Full article ">
(a) The inverse decay time values vs. the square wavevector for mixtures of Aerosol OT 0.03 M with PMAO 0.0824% w:w. (b) Variation of the apparent hydrodynamic radius of vesicles with PMAO concentration. The open circle represented on the PMAO concentration of 10−4% corresponds to the hydrodynamic radius of Aerosol OT vesicles. The Aerosol OT concentration was kept constant at 0.03 M. Full article ">
Changes on the apparent hydrodynamic radius values with the polymer concentration for vesicles prepared with Aerosol OT 0.03M and different PA concentration. The open circle represented on (PA) = 10−6% corresponds to the hydrodynamic radius of Aerosol OT vesicles. Full article ">
ζ-potential values for vesicles prepared with 0.03 M Aerosol OT and different polymer concentrations. Solid circles represent results for PA/Aerosol OT vesicles and triangles for PMAO/Aerosol OT mixtures. The ζ-potential of Aerosol OT vesicles is represented as the open circle. The dotted line shows the limit ζ-potential value for stable vesicles, see text. The solid line is a visual guide of the tendency. Full article ">
Molecular structures of the surfactant Aerosol OT and the polymers: poly(maleic anhydride-alt-1-octadecen) (PMAO) and poly(allylamine) (PA). Full article ">

559 KiB

Open AccessArticle

Evaluation of the Biological Effects of Externally Tunable, Hydrogel Encapsulated Quantum Dot Nanospheres in Escherichia coli

by Somesree GhoshMitra, Tong Cai, David Diercks, Zhibing Hu, James Roberts, Jai Dahiya, Nathaniel Mills, DiAnna Hynds and Santaneel Ghosh

Polymers 2011, 3(3), 1243-1254; https://doi.org/10.3390/polym3031243 - 8 Aug 2011

Cited by 4 | Viewed by 8793

Abstract

Quantum Dots (QDs) have become an interesting subject of study for labeling and drug delivery in biomedical research due to their unique responses to external stimuli. In this paper, the biological effects of a novel hydrogel based QD nano-structure on E. coli bacteria [...] Read more.

Quantum Dots (QDs) have become an interesting subject of study for labeling and drug delivery in biomedical research due to their unique responses to external stimuli. In this paper, the biological effects of a novel hydrogel based QD nano-structure on E. coli bacteria are presented. The experimental evidence reveals that cadmium telluride (CdTe) QDs that are encapsulated inside biocompatible polymeric shells have reduced or negligible toxicity to this model cell system, even when exposed at higher dosages. Furthermore, a preliminary gene expression study indicates that QD-hydrogel nanospheres do not inhibit the Green Fluorescent Protein (GFP) gene expression. As the biocompatible and externally tunable polymer shells possess the capability to control the QD packing density at nanometer scales, the resulting luminescence efficiency of the nanostructures, besides reducing the cytotoxic potential, may be suitable for various biomedical applications. Full article

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1174 KiB

Open AccessReview

Thermoresponsive Polymers for Biomedical Applications

by Mark A. Ward and Theoni K. Georgiou

Polymers 2011, 3(3), 1215-1242; https://doi.org/10.3390/polym3031215 - 3 Aug 2011

Cited by 961 | Viewed by 64442

Abstract

Thermoresponsive polymers are a class of “smart” materials that have the ability to respond to a change in temperature; a property that makes them useful materials in a wide range of applications and consequently attracts much scientific interest. This review focuses mainly on [...] Read more.

Thermoresponsive polymers are a class of “smart” materials that have the ability to respond to a change in temperature; a property that makes them useful materials in a wide range of applications and consequently attracts much scientific interest. This review focuses mainly on the studies published over the last 10 years on the synthesis and use of thermoresponsive polymers for biomedical applications including drug delivery, tissue engineering and gene delivery. A summary of the main applications is given following the different studies on thermoresponsive polymers which are categorized based on their 3-dimensional structure; hydrogels, interpenetrating networks, micelles, crosslinked micelles, polymersomes, films and particles. Full article

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Graphical abstract

657 KiB

Open AccessArticle

Dark Antimicrobial Mechanisms of Cationic Phenylene Ethynylene Polymers and Oligomers against Escherichia coli

by Ying Wang, Zhijun Zhou, Jingshu Zhu, Yanli Tang, Taylor D. Canady, Eva Y. Chi, Kirk S. Schanze and David G. Whitten

Polymers 2011, 3(3), 1199-1214; https://doi.org/10.3390/polym3031199 - 29 Jul 2011

Cited by 43 | Viewed by 10885

Abstract

The interactions of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) with E. coli cells are investigated to gain insights into the differences in the dark killing mechanisms between CPEs and OPEs. A laboratory strain of E. coli with antibiotic [...] Read more.

The interactions of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) with E. coli cells are investigated to gain insights into the differences in the dark killing mechanisms between CPEs and OPEs. A laboratory strain of E. coli with antibiotic resistance is included in this work to study the influence of antibiotic resistance on the antimicrobial activity of the CPEs and OPEs. In agreement with our previous findings, these compounds can efficiently perturb the bacterial cell wall and cytoplasmic membrane, resulting in bacterial cell death. Electron microscopy imaging and cytoplasmic membrane permeability assays reveal that the oligomeric OPEs penetrate the bacterial outer membrane and interact efficiently with the bacterial cytoplasmic membrane. In contrast, the polymeric CPEs cause serious damage to the cell surface. In addition, the minimum inhibitory concentration (MIC) and hemolytic concentration (HC) of the CPEs and OPEs are also measured to compare their antimicrobial activities against two different strains of E. coli with the compounds’ toxicity levels against human red blood cells (RBC). MIC and HC measurements are in good agreement with our previous model membrane perturbation study, which reveals that the different membrane perturbation abilities of the CPEs and OPEs are in part responsible for their selectivity towards bacteria compared to mammalian cells. Our study gives insight to several structural features of the PPE-based CPEs and OPEs that modulate their antimicrobial properties and that these features can serve as a basis for further tuning their structures to optimize antimicrobial properties. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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Graphical abstract

Graphical abstract
Full article ">
Images of E. coli cells (ATCC 11303, ∼108 CFU/mL) exposed to 10 μg/mL of antimicrobials at 37 °C for one hour in the dark. A, E coli cells alone; B, Melittin; C, OPE-1; D, OPE-3; E, EO-OPE-1(C3); F, EO-OPE-1(Th); G, PPE-DABCO; H, PPE-Th. The bottom figure is a close up of E. coli suspensions in glass vials of A and E. Full article ">
Antimicrobial activities of cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) against E. coli cells. Exponential growth phase E. coli cells (∼108 CFU/mL) were incubated with 10 μg/mL CPEs or OPEs at 37 °C for one hour in the dark followed by 106 fold dilution. The diluted samples were loaded on Luria broth plates. The reported survival percentage is the average of two independent experiments and normalized to the control. Full article ">
SEM images of E. coli (ATCC 11303) cells (108 CFU/mL) incubated with 10 μg/mL antimicrobial compounds for one hour in the dark. The scale bars of these images are 4 μm. Full article ">
SEM images of E. coli BL21(DE3)pLysS cells (108 CFU/mL) incubated with 10 μg/mL antimicrobial compounds for one hour in the dark. The scale bars of these images are 3 μm. Full article ">
Circular dichroism spectra of BSA (0.1 mg/mL) and its complexes with CPEs (10 μg/mL) in phosphate buffer at room temperature. CPEs alone do not have any circular dichroism signal. Full article ">
Structures of the antimicrobial compounds used in this study. n denotes the number of repeat units. Full article ">

555 KiB

Open AccessArticle

Microspheres Containing Cibacron Blue F3G-A and Incorporated Iron Oxide Nanoparticles as Biomarker Harvesting Platforms

by Alexis Patanarut, Elissa H. Williams, Emanuel Petricoin, Lance A. Liotta and Barney Bishop

Polymers 2011, 3(3), 1181-1198; https://doi.org/10.3390/polym3031181 - 28 Jul 2011

Cited by 4 | Viewed by 9233

Abstract

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein [...] Read more.

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein species. The dye-loaded magnetic particles were physically characterized, and their protein sequestration performance was investigated. The results of these studies indicated that dye-loaded magnetic particles sequestered a greater amount of lower molecular weight proteins from the test solution than was achieved using reference particles, dye-loaded cross-linked N-isopropylacrylamide-based core-shell particles. This difference in protein harvesting ability may reflect the higher degree of dye-loading in the magnetic particles relative to the dye-loaded core-shell particles. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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Sequestered low molecular weight species can diffuse out of underivatized hydrogel particles (A); Incorporation of affinity bait within the particle matrix enables the particle to effectively retain the harvested low molecular weight species and prevent them from escaping the particle matrix (B). Full article ">
Hydrogel particles based on pAm were generated using precipitation polymerization in ethanol using azobisisobutyronitrile (AIBN) as the initiator and N-N′-methylenebis(acrylamide) (BIS) as the cross-linker. Magnetic functionality was introduced to the particles via the in situ coprecipitation of Fe(II) and Fe(III) in the polymer network (A); Amine groups are introduced to the magnetic particles via Hofmann degradation (B); Cibacron Blue F3G-A was covalently bound to the aminated magnetic particles to fabricate dye-loaded magnetic hydrogel particles (C). Full article ">
Comparison of the plain pAm hydrogel particles with the different derivations of the 50MHP (A), 75MHP (B) and 100MHP (C) show an increase in swelling capacity with increasing pH and increasing iron content. Plain pAm particles treated with the same conditions used for the in situ iron oxide precipitation (D) also exhibited increased swelling capacity with increasing pH. Full article ">
Scanning electron microscopy (SEM) image of pAm-based hydrogel particles (A) prepared via precipitation polymerization in ethanol revealed monodisperse spherical particles. These particles were used to generate magnetic hydrogel particles (B), which were prepared via in situ coprecipitation of iron oxide nanoparticles within the hydrogel matrix. Full article ">
SDS-PAGE analysis of dye-loaded core-shell particles and dye-loaded magnetic hydrogel particles incubated with MW markers: (1) MW ladder; (2) model protein solution; (3) supernatant from dye-loaded core-shell particles; (4) bound by dye-loaded core-shell particles; (5) supernatant from dye-loaded magnetic hydrogel particles; (6) bound by dye-loaded magnetic hydrogel particles. Full article ">
SDS-PAGE analysis of dye-loaded magnetic and intermediate pAm particles with varied iron oxide content incubated with MW markers: (1) MW ladder; (2) model protein solution; (3) supernatant from pAm particles; (4) bound by pAm particles; (5) supernatant from 100MHP; (6) bound by 100MHP; (7) supernatant from aminated 100MHP; (8) bound by aminated 100MHP; (9) supernatant from dye-loaded 100MHP; (10) bound by dye-loaded 100MHP. Full article ">

272 KiB

Open AccessReview

Polymer-Optical-Fiber Lasers and Amplifiers Doped with Organic Dyes

by Jon Arrue, Felipe Jiménez, Igor Ayesta, M. Asunción Illarramendi and Joseba Zubia

Polymers 2011, 3(3), 1162-1180; https://doi.org/10.3390/polym3031162 - 25 Jul 2011

Cited by 62 | Viewed by 8923

Abstract

Polymer optical fibers (POFs) doped with organic dyes can be used to make efficient lasers and amplifiers due to the high gains achievable in short distances. This paper analyzes the peculiarities of light amplification in POFs through some experimental data and a computational [...] Read more.

Polymer optical fibers (POFs) doped with organic dyes can be used to make efficient lasers and amplifiers due to the high gains achievable in short distances. This paper analyzes the peculiarities of light amplification in POFs through some experimental data and a computational model capable of carrying out both power and spectral analyses. We investigate the emission spectral shifts and widths and on the optimum signal wavelength and pump power as functions of the fiber length, the fiber numerical aperture and the radial distribution of the dopant. Analyses for both step-index and graded-index POFs have been done. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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4103 KiB

Open AccessArticle

Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

by Kevin Lamberts, Irmgard Kalf, Amr Ramadan, Paul Müller, Richard Dronskowski and Ulli Englert

Polymers 2011, 3(3), 1151-1161; https://doi.org/10.3390/polym3031151 - 25 Jul 2011

Cited by 17 | Viewed by 8580

Abstract

The chain polymer [{Cd(μ-X)₂py₂}¹_∞] (X = Cl, Br; py = pyridine) undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and [...] Read more.

The chain polymer [{Cd(μ-X)₂py₂}¹_∞] (X = Cl, Br; py = pyridine) undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples. Full article

(This article belongs to the Special Issue Coordination Polymers)

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View on crystallographic B-face of (a): 1α and (b): 1β (color code: Cd: yellow, Br: green, N: blue, C: black, H: grey) [<a href="#b12-polymers-03-01151" class="html-bibr">12</a>]. Full article ">
Measured chemical composition as function of reactant stoichiometry for microanalysis (CHN), ion chromatography (IC) and single-crystal X-ray diffraction (SCXRD). Full article ">
X-ray powder diffractograms of 1_30,1_70 and 2 at ambient temperature showing a shift towards higher diffraction angles with increasing chlorine ratio. Full article ">
(a): Dependence of the transition temperature determined by single-crystal X-ray diffraction (SCXRD) and X-ray powder diffraction (XRPD) on the chemical composition determined by ion chromatography. (b): 2D-plot example from 1_10 of temperature dependent XRPD measurements showing splitting of the orthorhombic 3 1 1 reflection to the monoclinic 3 1 1 and 3 1 1̄ reflections at transition temperature. Full article ">
Unit cell volume and Cd⋯Cd distance (lattice parameter c) dependency on halide ratio displaying Vegard behavior (line suggests ideal values). Parameters from SCXRD (see <a href="#t1-polymers-03-01151" class="html-table">Tables 1</a> and <a href="#t2-polymers-03-01151" class="html-table">2</a>) and halide ratio from ion chromatography. Full article ">
Structural formula of <math display="inline"> <semantics id="sm9"> <mrow> <mrow> <mo>[</mo> <mrow> <msubsup> <mrow> <mrow> <mo>{</mo> <mrow> <mtext>Cd</mtext> <msub> <mrow> <mrow> <mo>(</mo> <mrow> <mi>μ</mi> <mo>−</mo> <mtext>Br</mtext></mrow> <mo>)</mo></mrow></mrow> <mrow> <mn>2</mn> <mo>−</mo> <mn>2</mn> <mi>x</mi></mrow></msub> <msub> <mrow> <mrow> <mo>(</mo> <mrow> <mi>μ</mi> <mo>−</mo> <mtext>Cl</mtext></mrow> <mo>)</mo></mrow></mrow> <mrow> <mn>2</mn> <mi>x</mi></mrow></msub> <msub> <mrow> <mtext>py</mtext></mrow> <mn>2</mn></msub></mrow> <mo>}</mo></mrow></mrow> <mo>∞</mo> <mn>1</mn></msubsup></mrow> <mo>]</mo></mrow></mrow></semantics></math> showing one-dimensional extension of the polymer chain (left) and naming convention (right). Full article ">
Symmetry relation of high-temperature (1α) and low-temperature (1β) phase. Full article ">

689 KiB

Open AccessArticle

Towards Extrusion of Ionomers to Process Fuel Cell Membranes

by Yannick Molmeret, France Chabert, Nadia El Kissi, Cristina Iojoiu, Regis Mercier and Jean-Yves Sanchez

Polymers 2011, 3(3), 1126-1150; https://doi.org/10.3390/polym3031126 - 19 Jul 2011

Cited by 13 | Viewed by 8803

Abstract

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, [...] Read more.

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, the feasibility to extrude composites was demonstrated. The impact of the plasticizers on the melt viscosity was investigated. Following the extrusion, the plasticizers were fully removed in water. The extrusion was found to impact neither on the ionomer chains, nor on the performances of the membrane. This environmentally friendly process was successfully validated for a variety of high performance ionomers. Full article

(This article belongs to the Special Issue Conductive Polymers)

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Structural formula of sulfonated polysulfone (SPSFH). Full article ">
Extrusion temperature range for Udel sulfonated polysulfone in acidic and alkaline forms compared with pristine PSF (Udel P-3500). Full article ">
Photographs from left to right of: extruded commercial PSF (Udel P3500) at 300 °C, SPSFH (IEC = 1.35 H+/kg) form at 210 °C, SPSFNa (IEC = 1.3 Na+/kg) form at 320 °C. Full article ">
Tg of SPSFNa (IEC = 1.3 Na+/kg)/sorbitol blends versus sorbitol content. Full article ">
Time-temperature superposition of the SPSFNa (IEC = 1.3 Na+/kg) + 40% PEG blend, Reference temperature = 160 °C. Full article ">
Viscosity at 1 rad s−1 vs. the volume content in plasticizer for SPSFNa (IEC = 1.3 Na+/kg) blended with PEG, polyol and sorbitol. Full article ">
Tg of SPSFH (IEC = 1.35 H+/kg) blends as a function of plasticizer content. Full article ">
Effect of PEG, imidazole, TESA plasticizers on the viscosity of SPSFH (IEC = 1.35 H+/kg) blends. Full article ">
Time-Temperature Superposition obtained for SPSFH (IEC = 1.35 H+/kg) blended with 30% PEG. Full article ">

387 KiB

Open AccessArticle

In Vitro and In Vivo Evaluation of a Folate-Targeted Copolymeric Submicrohydrogel Based on N-Isopropylacrylamide as 5-Fluorouracil Delivery System

by M. Dolores Blanco, Sandra Guerrero, Marta Benito, Ana Fernández, César Teijón, Rosa Olmo, Issa Katime and José M. Teijón

Polymers 2011, 3(3), 1107-1125; https://doi.org/10.3390/polym3031107 - 18 Jul 2011

Cited by 28 | Viewed by 10318

Abstract

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in [...] Read more.

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in 8 h. The cytotoxicity of unloaded F-SubMGs in MCF7 and HeLa cells was low; although it increased for high F-SubMG concentration. The administration of 10 μM 5-FU by 5-FU-loaded F-SubMGs was effective on both cellular types. Cell uptake of F-SubMGs took place in both cell types, but it was higher in HeLa cells because they are folate receptor positive. After subcutaneous administration (28 mg 5-FU/kg b.w.) in Wistar rats, F-SubMGs were detected at the site of injection under the skin. Histological studies indicated that the F-SubMGs were surrounded by connective tissue, without any signs of rejections, even 60 days after injection. Pharmacokinetic study showed an increase in MRT (mean residence time) of 5-FU when the drug was administered by drug-loaded F-SubMGs. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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1957 KiB

Open AccessArticle

Mechanical Properties and Adhesion of a Micro Structured Polymer Blend

by Brunero Cappella

Polymers 2011, 3(3), 1091-1106; https://doi.org/10.3390/polym3031091 - 15 Jul 2011

Cited by 22 | Viewed by 8155

Abstract

A 50:50 blend of polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA) has been characterized with an Atomic Force Microscope (AFM) in Tapping Mode and with force-distance curves. The polymer solution has been spin-coated on a glass slide. PnBMA builds a uniform film on the [...] Read more.

A 50:50 blend of polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA) has been characterized with an Atomic Force Microscope (AFM) in Tapping Mode and with force-distance curves. The polymer solution has been spin-coated on a glass slide. PnBMA builds a uniform film on the glass substrate with a thickness of @200 nm. On top of it, the PS builds an approximately 100 nm thick film. The PS-film undergoes dewetting, leading to the formation of holes surrounded by about 2 µm large rims. In those regions of the sample, where the distance between the holes is larger than about 4 µm, light depressions in the PS film can be observed. Topography, dissipated energy, adhesion, stiffness and elastic modulus have been measured on these three regions (PnBMA, PS in the rims and PS in the depressions). The two polymers can be distinguished in all images, since PnBMA has a higher adhesion and a smaller stiffness than PS, and hence a higher dissipated energy. Moreover, the polystyrene in the depressions shows a very high adhesion (approximately as high as PnBMA) and its stiffness is intermediate between that of PnBMA and that of PS in the rims. This is attributed to higher mobility of the PS chains in the depressions, which are precursors of new holes. Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes)

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Graphical abstract

Graphical abstract
Full article ">
Topography (A) and phase-shift (B) image of a 40 × 40 μm2 area of the poly(n-butyl methacrylate) (PnBMA)/polystyrene (PS) blend, acquired in Tapping Mode. The white and black line in both pictures indicates the position of the line profile shown in panel (C). PnBMA (darker in panel A and brighter in panel B) forms a film in contact with the glass substrate; PS (brighter in panel A and darker in panel B) stays on top of PnBMA and, due to the immiscibility of the two polymers, forms holes to minimize the contact surface. The phase shift is higher on PnBMA than on PS, due to larger adhesion and compliance. The bottom of the holes present several droplet-like PS particles, two of which are indicated by the second and third arrow on the right in panel C. The phase shift on such particles is very large, due to topography artifacts. The PS film presents several depressions (one is indicated by the first arrow on the left in panel C), on which the phase shift is similar to that on PnBMA. Full article ">
Topography (a) and phase-shift (b) image of a 60 × 60 μm2 area of the PnBMA/PS blend, acquired in Tapping Mode. The white square indicates the position of the 14 × 14 μm2 section, magnified in the insets, where the Force Volume measurement has been performed. This section contains a large depression. Full article ">
Force-distance curves on PnBMA (grey) and PS (black). The maximum force is 3 μN. Arrows indicate the direction of motion. PnBMA has a larger adhesion and a lower stiffness than PS. Full article ">
(a) Adhesion force map of the sample. PnBMA (brighter) has a larger adhesion than PS, but the PS in the depression has an adhesion comparable with that of PnBMA. The adhesion force map resembles the phase shift image (<a href="#f2-polymers-03-01091" class="html-fig">Figure 2</a>(b)). (b) Histograms of the adhesion on the whole area (black line), on the PS film (dark grey bars), on the depression (light grey bars), and on the PnBMA film in the holes (white bars). The histograms of PnBMA, (Fadh = 0.71 ± 0.04 μN) is separated from that of PS (Fadh = 0.42 ± 0.08 μN), but not from that of the depression (Fadh = 0.68 ± 0.5 μN). Full article ">
(a) Stiffness map of the sample. PnBMA (darker) is less stiff than PS. The PS in the depression has an intermediate stiffness between that of PnBMA and of PS. (b) Histograms of the stiffness on the whole area (black line), on the PS film (dark grey bars), on the depression (light grey bars), and on the PnBMA film in the holes (white bars). The three histograms are separated (S = 0.89 ± 0.03 for PS, 0.85 ± 0.02 for the depression and 0.81 ± 0.04 for PnBMA). Full article ">
Mean deformation-force curves (grey circles) of PnBMA (top), the depression (middle) and PS (bottom). The curves are fitted with the Hertz formula for a semispherical tip (<a href="#FD7" class="html-disp-formula">Equation (7)</a>). Full article ">
(a) Map of the elastic modulus of the sample. PnBMA (darker) has a lower modulus than PS. The PS in the depression has an intermediate modulus between that of PnBMA and of PS. (b) Histograms of the logarithm of the Young's modulus on the whole area (black line), on the PS film (dark grey bars), on the depression (light grey bars), and on the PnBMA film in the holes (white bars). The three histograms are separated (log(E) = 9.6 ± 0.15 for PnBMA, 9.8 ± 0.13 for the depression and 10 ± 0.2 for PS). Full article ">

328 KiB

Open AccessReview

Multimeric, Multifunctional Derivatives of Poly(ethylene glycol)

by Marina Zacchigna, Francesca Cateni, Sara Drioli and Gian Maria Bonora

Polymers 2011, 3(3), 1076-1090; https://doi.org/10.3390/polym3031076 - 13 Jul 2011

Cited by 29 | Viewed by 9893

Abstract

This article reviews the use of multifunctional polymers founded on high-molecular weight poly(ethylene glycol) (PEG). The design of new PEG derivatives assembled in a dendrimer-like multimeric fashion or bearing different functionalities on the same molecule is described. Their use as new drug delivery [...] Read more.

This article reviews the use of multifunctional polymers founded on high-molecular weight poly(ethylene glycol) (PEG). The design of new PEG derivatives assembled in a dendrimer-like multimeric fashion or bearing different functionalities on the same molecule is described. Their use as new drug delivery systems based on the conjugation of multiple copies or diversely active drugs on the same biocompatible support is illustrated. Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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Graphical abstract

252 KiB

Open AccessArticle

Thermal Cloud Point Fractionation of Poly(vinyl alcohol-co-vinyl acetate): Partition of Nanogels in the Fractions

by Leonard I. Atanase and Gérard Riess

Polymers 2011, 3(3), 1065-1075; https://doi.org/10.3390/polym3031065 - 4 Jul 2011

Cited by 12 | Viewed by 8696

Abstract

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get [...] Read more.

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get an insight in the partition of the initially present nanogels in the different fractions. All the fractions were characterized by size exclusion chromatography (SEC), NMR and dynamic light scattering (DLS) giving access to average degree of polymerization , DPw average degree of hydrolysis DH, average sequence lengths of vinyl acetate VAc, volume fraction and average size diameter (Dv) of nanogels and “free PVA chains”. The polydispersity of the samples in DPw, DH and VAc could be confirmed. The nanogels characterized by the highest values of volume fraction and Dv, in the range of 40–43 nm, were separated in the first coacervate fraction, whereas the most soluble fraction with low VAc content does not contain nanogels but only “free chains” of a Dv value of around 7–8 nm. The nanogels in the various fractions could further be disaggregated into “free chains” by complex formation with sodium dodecyl sulfate (SDS). Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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DLS-size distributions: Dv for the non-fractionated samples PVA-73-650 and PVA-73-685. A representing the “free chains” and B the nanogels peaks. Full article ">
Schematic representation of the different fractionation steps. Molecular characteristics of the phases in equilibrium for sample PVA-73-650 and PVA-73-685 with <math display="inline"> <semantics id="sm46"> <mrow> <mover accent="true"> <mrow> <mtext>DH</mtext></mrow> <mo>¯</mo></mover></mrow></semantics></math>-average degree of hydrolysis, <math display="inline"> <semantics id="sm47"> <mrow> <mover accent="true"> <mrow> <mtext>DPw</mtext></mrow> <mo>¯</mo></mover></mrow></semantics></math>-weight average degree of polymerization, <math display="inline"> <semantics id="sm48"> <mrow> <mover accent="true"> <mrow> <msubsup> <mtext>n</mtext> <mn>0</mn> <mrow> <mtext>VAc</mtext></mrow></msubsup></mrow> <mo>¯</mo></mover></mrow></semantics></math>-average sequence length of vinyl acetate and Wi-weight %. Full article ">
DLS-size distributions: Dv for fractions F0, F1 and F4 of sample PVA-73-650 (1 wt% solution at 20 °C); F0 being the non-fractioned sample. Full article ">
DLS-size distributions: Dv for fraction F1 of sample PVA-73-685 (1 wt% solution at 20 °C) at different SDS concentrations indicated with respect to PVA. Full article ">

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Polymers, Volume 3, Issue 3 (September 2011) – 36 articles , Pages 975-1574

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