Langmuir : the ACS journal of surfaces and colloids, Jan 17, 2016
We investigate the effect of shape on reversible adsorption kinetics using colloidal polystyrene ... more We investigate the effect of shape on reversible adsorption kinetics using colloidal polystyrene dimers near a solid glass surface as a model system. The interaction between colloid and wall is tuned using electrostatic, depletion, and gravity forces to produce a double-well potential. The dwell time in each of the potential wells is measured from long duration particle trajectories. The height of each monomer relative to the glass surface is measured to a resolution of <20 nm by in-line holographic microscopy. The measured transition probability distributions are used in kinetic equations to describe the flux of particles to and from the surface. The dimers are compared to independent isolated monomers to determine the effects of shape on adsorption equilibria and kinetics. To elucidate these differences, we consider both mass and surface coverage and two definitions of surface coverage. The results show that dimers with single coverage produce slower adsorption, lower surface c...
High viscosity is a major challenge with protein therapeutics at extremely high concentrations. T... more High viscosity is a major challenge with protein therapeutics at extremely high concentrations. To overcome this obstacle, it is essential to understand the relationship between the concentration of a protein solution and its viscosity as a function of shear rate and temperature. Here, lysozyme is a model charged globular protein having both short-ranged attraction (SA) and long-ranged repulsion (LR) that promote the formation of dynamic clusters at high concentrations. We report viscosity measurements from a micro-capillary rheometer (using only several microliters of solution) over a wide range of lysozyme solution concentrations, shear rates, and temperatures. Solution structural relaxation dynamics are also probed by dynamic light scattering (DLS). As a result of lysozyme's SALR interactions, the viscosity increased dramatically across all shear rates with increasing concentration and decreasing temperature. While most of the solutions exhibited Newtonian behavior, shear thi...
Cubic colloids, sedimented on a surface and immersed in a solution of depletant molecules, were m... more Cubic colloids, sedimented on a surface and immersed in a solution of depletant molecules, were modeled with a family of shapes which smoothly varies from squares to circles. Using Wang-Landau simulations with expanded ensembles, we observe the formation of rhombic lattices, square lattices, hexagonal lattices, and a fluid phase. This systematic investigation includes locating transitions between all combinations of the three lattice structures upon changing the shape and transitions between the fluid and crystal upon changing the depletant concentration. The rhombic lattice deforms smoothly between square-like and hexagonal-like angles, depending on both the shape and the depletant concentration. Our results on the effect of the depletant concentration, depletant size, and colloid shape to influence the stability of the fluid and the lattice structures may help guide experimental studies with recently synthesized cubic colloids.
The glass transition of colloidal dispersions interacting with both a short-ranged attraction and... more The glass transition of colloidal dispersions interacting with both a short-ranged attraction and long-ranged repulsion is studied using highly purified lysozyme solutions. Newtonian liquid behavior is observed at all conditions while measurements of the dynamics in the short-time limit show features typical of glassy colloidal systems at high protein concentrations. This interesting behavior is due to the competition of the attraction and repulsion that produces a heterogeneous microstructure only at intermediate range length scales. The results demonstrate that theories for the macroscopic properties of systems with competing interactions need to include intermediate range order.
Individual cube-like ‘superball’ shaped colloids are hydrodynamically similar to colloidal sphere... more Individual cube-like ‘superball’ shaped colloids are hydrodynamically similar to colloidal spheres, yet their interactions at moderate volume fractions are markedly shape-mediated, affecting the suspension micro-structure, particle diffusion and shear thickening behavior.
Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can r... more Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can result in the production of unwanted subvisible protein particles (SVPs). In this work, surface-mediated SVP formation was investigated. Specifically, the effects of different solid interface materials, interfacial shear rates, and protein concentrations on SVP formation were measured for the National Institute of Standards and Technology monoclonal antibody (NISTmAb), a reference IgG1 monoclonal antibody (mAb). A stainless steel rotary piston pump was used to identify formulation and process parameters that affect aggregation, and a flow cell (alumina or stainless steel interface) was used to further investigate the effect of different interface materials and/or interfacial shear rates. SVP particles produced were monitored using flow microscopy or flow cytometry. Neutron reflectometry and a quartz crystal microbalance with dissipation monitoring were used to characterize adsorption and ...
Memory effects, including shape, chirality, and liquid-crystallinity, have enabled macroscopic ma... more Memory effects, including shape, chirality, and liquid-crystallinity, have enabled macroscopic materials with novel functions. However, the generation of complex supramolecular nanosystems via memory effects has not yet been investigated. Here, we report a cyclotriveratrylene-crown (CTV) compound that self-assembles into supramolecular columns and spheres forming, respectively, hexagonal and cubic mesophases. Upon transition from one phase to the other, an epitaxial relationship holds, via an unprecedented supramolecular orientational memory effect. Specifically, the molecular orientation and columnar character of supramolecular packing is preserved in the cubic phase, providing an otherwise inaccessible structure comprising orthogonally oriented domains of supramolecular columns. The continuous columnar character of tetrahedrally distorted supramolecular spheres self-organized from the CTV derivative in the faces of the Pm3Ì…n lattice is the basis of this supramolecular orientationa...
A silk nanofiber composite network produced by forming a solution of silk fiber and hexafluroisop... more A silk nanofiber composite network produced by forming a solution of silk fiber and hexafluroisopropanol, wherein the step of forming is devoid of any acid treatment, where the silk solution has a concentration of about 0.2 to about 1.5 weight percent silk in hexafluroisopropanol, and where the silk is selected from Bombyx mori silk and Nephila clavipes silk; and electrospinning the solution, thereby forming a non-woven network of nanofibers having a diameter in the range from about 2 to about 2000 nanometers
2009 International Semiconductor Device Research Symposium, 2009
In this work, poly(2,5-Bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT), a state-of-the-ar... more In this work, poly(2,5-Bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT), a state-of-the-art solution-processable semiconducting polymer with field-effect hole mobility as high as 0.1-1 cm2/V s, was used for grain mapping. The large, terraced crystals of pBTTT that form in spin-cast thin films after heating to a mesophase on a hydrophobic substrate extend laterally for microns and vertically throughout the film thickness, making it a suitable material for imaging compared with other semiconducting polymers. By using dark-field (DF) transmission electron microscopy (TEM), we found that the characteristic terraced structure of a pBTTT with tetradecyl side chains (pBTTT-C14) is made up of micron- or submicron-sized crystalline grains which contain even smaller nanocrystals.
Langmuir : the ACS journal of surfaces and colloids, Jan 17, 2016
We investigate the effect of shape on reversible adsorption kinetics using colloidal polystyrene ... more We investigate the effect of shape on reversible adsorption kinetics using colloidal polystyrene dimers near a solid glass surface as a model system. The interaction between colloid and wall is tuned using electrostatic, depletion, and gravity forces to produce a double-well potential. The dwell time in each of the potential wells is measured from long duration particle trajectories. The height of each monomer relative to the glass surface is measured to a resolution of <20 nm by in-line holographic microscopy. The measured transition probability distributions are used in kinetic equations to describe the flux of particles to and from the surface. The dimers are compared to independent isolated monomers to determine the effects of shape on adsorption equilibria and kinetics. To elucidate these differences, we consider both mass and surface coverage and two definitions of surface coverage. The results show that dimers with single coverage produce slower adsorption, lower surface c...
High viscosity is a major challenge with protein therapeutics at extremely high concentrations. T... more High viscosity is a major challenge with protein therapeutics at extremely high concentrations. To overcome this obstacle, it is essential to understand the relationship between the concentration of a protein solution and its viscosity as a function of shear rate and temperature. Here, lysozyme is a model charged globular protein having both short-ranged attraction (SA) and long-ranged repulsion (LR) that promote the formation of dynamic clusters at high concentrations. We report viscosity measurements from a micro-capillary rheometer (using only several microliters of solution) over a wide range of lysozyme solution concentrations, shear rates, and temperatures. Solution structural relaxation dynamics are also probed by dynamic light scattering (DLS). As a result of lysozyme's SALR interactions, the viscosity increased dramatically across all shear rates with increasing concentration and decreasing temperature. While most of the solutions exhibited Newtonian behavior, shear thi...
Cubic colloids, sedimented on a surface and immersed in a solution of depletant molecules, were m... more Cubic colloids, sedimented on a surface and immersed in a solution of depletant molecules, were modeled with a family of shapes which smoothly varies from squares to circles. Using Wang-Landau simulations with expanded ensembles, we observe the formation of rhombic lattices, square lattices, hexagonal lattices, and a fluid phase. This systematic investigation includes locating transitions between all combinations of the three lattice structures upon changing the shape and transitions between the fluid and crystal upon changing the depletant concentration. The rhombic lattice deforms smoothly between square-like and hexagonal-like angles, depending on both the shape and the depletant concentration. Our results on the effect of the depletant concentration, depletant size, and colloid shape to influence the stability of the fluid and the lattice structures may help guide experimental studies with recently synthesized cubic colloids.
The glass transition of colloidal dispersions interacting with both a short-ranged attraction and... more The glass transition of colloidal dispersions interacting with both a short-ranged attraction and long-ranged repulsion is studied using highly purified lysozyme solutions. Newtonian liquid behavior is observed at all conditions while measurements of the dynamics in the short-time limit show features typical of glassy colloidal systems at high protein concentrations. This interesting behavior is due to the competition of the attraction and repulsion that produces a heterogeneous microstructure only at intermediate range length scales. The results demonstrate that theories for the macroscopic properties of systems with competing interactions need to include intermediate range order.
Individual cube-like ‘superball’ shaped colloids are hydrodynamically similar to colloidal sphere... more Individual cube-like ‘superball’ shaped colloids are hydrodynamically similar to colloidal spheres, yet their interactions at moderate volume fractions are markedly shape-mediated, affecting the suspension micro-structure, particle diffusion and shear thickening behavior.
Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can r... more Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can result in the production of unwanted subvisible protein particles (SVPs). In this work, surface-mediated SVP formation was investigated. Specifically, the effects of different solid interface materials, interfacial shear rates, and protein concentrations on SVP formation were measured for the National Institute of Standards and Technology monoclonal antibody (NISTmAb), a reference IgG1 monoclonal antibody (mAb). A stainless steel rotary piston pump was used to identify formulation and process parameters that affect aggregation, and a flow cell (alumina or stainless steel interface) was used to further investigate the effect of different interface materials and/or interfacial shear rates. SVP particles produced were monitored using flow microscopy or flow cytometry. Neutron reflectometry and a quartz crystal microbalance with dissipation monitoring were used to characterize adsorption and ...
Memory effects, including shape, chirality, and liquid-crystallinity, have enabled macroscopic ma... more Memory effects, including shape, chirality, and liquid-crystallinity, have enabled macroscopic materials with novel functions. However, the generation of complex supramolecular nanosystems via memory effects has not yet been investigated. Here, we report a cyclotriveratrylene-crown (CTV) compound that self-assembles into supramolecular columns and spheres forming, respectively, hexagonal and cubic mesophases. Upon transition from one phase to the other, an epitaxial relationship holds, via an unprecedented supramolecular orientational memory effect. Specifically, the molecular orientation and columnar character of supramolecular packing is preserved in the cubic phase, providing an otherwise inaccessible structure comprising orthogonally oriented domains of supramolecular columns. The continuous columnar character of tetrahedrally distorted supramolecular spheres self-organized from the CTV derivative in the faces of the Pm3Ì…n lattice is the basis of this supramolecular orientationa...
A silk nanofiber composite network produced by forming a solution of silk fiber and hexafluroisop... more A silk nanofiber composite network produced by forming a solution of silk fiber and hexafluroisopropanol, wherein the step of forming is devoid of any acid treatment, where the silk solution has a concentration of about 0.2 to about 1.5 weight percent silk in hexafluroisopropanol, and where the silk is selected from Bombyx mori silk and Nephila clavipes silk; and electrospinning the solution, thereby forming a non-woven network of nanofibers having a diameter in the range from about 2 to about 2000 nanometers
2009 International Semiconductor Device Research Symposium, 2009
In this work, poly(2,5-Bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT), a state-of-the-ar... more In this work, poly(2,5-Bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT), a state-of-the-art solution-processable semiconducting polymer with field-effect hole mobility as high as 0.1-1 cm2/V s, was used for grain mapping. The large, terraced crystals of pBTTT that form in spin-cast thin films after heating to a mesophase on a hydrophobic substrate extend laterally for microns and vertically throughout the film thickness, making it a suitable material for imaging compared with other semiconducting polymers. By using dark-field (DF) transmission electron microscopy (TEM), we found that the characteristic terraced structure of a pBTTT with tetradecyl side chains (pBTTT-C14) is made up of micron- or submicron-sized crystalline grains which contain even smaller nanocrystals.
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