Schweizer, Kenneth S.
Overview
Works:  45 works in 55 publications in 1 language and 66 library holdings 

Roles:  Author 
Publication Timeline
.
Most widely held works by
Kenneth S Schweizer
Structure of colloid polymer suspensions by
Matthias Fuchs(
)
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
Concentration Fluctuations in a Model ColloidPolymer Suspension experimental Tests of Depletion Theories by S Ramakrishnan(
)
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
Macromolecular theory of solvation and structure in mixtures of colloids and polymers by
Matthias Fuchs(
)
2 editions published between 2001 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2001 and 2007 in English and held by 2 WorldCat member libraries worldwide
Phase separation in suspensions of colloids, polymers and nanoparticles role of solvent quality, physical mesh, and nonlocal
entropic repulsion by YengLong Chen(
)
2 editions published between 2003 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2003 and 2007 in English and held by 2 WorldCat member libraries worldwide
Interference lithography for optical devices and coatings by Abigail T Juhl(
)
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Interference lithography can create largearea, defectfree nanostructures with unique optical properties. In this thesis, interference lithography will be utilized to create photonic crystals for functional devices or coatings. For instance, typical lithographic processing techniques were used to create 1, 2 and 3 dimensional photonic crystals in SU8 photoresist. These structures were infilled with birefringent liquid crystal to make active devices, and the orientation of the liquid crystal directors within the SU8 matrix was studied. Most of this thesis will be focused on utilizing polymerization induced phase separation as a singlestep method for fabrication by interference lithography. For example, layered polymer/nanoparticle composites have been created through the onestep twobeam interference lithographic exposure of a dispersion of 25 and 50 nm silica particles within a photopolymerizable mixture at a wavelength of 532 nm. In the areas of constructive interference, the monomer begins to polymerize via a freeradical process and concurrently the nanoparticles move into the regions of destructive interference. The holographic exposure of the particles within the monomer resin offers a singlestep method to anisotropically structure the nanoconstituents within a composite. A onestep holographic exposure was also used to fabricate self healing coatings that use water from the environment to catalyze polymerization. Polymerization induced phase separation was used to sequester an isocyanate monomer within an acrylate matrix. Due to the periodic modulation of the index of refraction between the monomer and polymer, the coating can reflect a desired wavelength, allowing for tunable coloration. When the coating is scratched, polymerization of the liquid isocyanate is catalyzed by moisture in air; if the indices of the two polymers are matched, the coatings turn transparent after healing. Interference lithography offers a method of creating multifunctional selfhealing coatings that readout when damage has occurred
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Interference lithography can create largearea, defectfree nanostructures with unique optical properties. In this thesis, interference lithography will be utilized to create photonic crystals for functional devices or coatings. For instance, typical lithographic processing techniques were used to create 1, 2 and 3 dimensional photonic crystals in SU8 photoresist. These structures were infilled with birefringent liquid crystal to make active devices, and the orientation of the liquid crystal directors within the SU8 matrix was studied. Most of this thesis will be focused on utilizing polymerization induced phase separation as a singlestep method for fabrication by interference lithography. For example, layered polymer/nanoparticle composites have been created through the onestep twobeam interference lithographic exposure of a dispersion of 25 and 50 nm silica particles within a photopolymerizable mixture at a wavelength of 532 nm. In the areas of constructive interference, the monomer begins to polymerize via a freeradical process and concurrently the nanoparticles move into the regions of destructive interference. The holographic exposure of the particles within the monomer resin offers a singlestep method to anisotropically structure the nanoconstituents within a composite. A onestep holographic exposure was also used to fabricate self healing coatings that use water from the environment to catalyze polymerization. Polymerization induced phase separation was used to sequester an isocyanate monomer within an acrylate matrix. Due to the periodic modulation of the index of refraction between the monomer and polymer, the coating can reflect a desired wavelength, allowing for tunable coloration. When the coating is scratched, polymerization of the liquid isocyanate is catalyzed by moisture in air; if the indices of the two polymers are matched, the coatings turn transparent after healing. Interference lithography offers a method of creating multifunctional selfhealing coatings that readout when damage has occurred
PolymerModeCoupling Theory of FiniteSizeFluctuation Effects in Entangled Solutions, Melts, and Gels. 2. Comparison with
Experiment by
Matthias Fuchs(
)
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
Structure and thermodynamics of colloidpolymer mixtures a macromolecular approach by
Matthias Fuchs(
)
2 editions published between 2000 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2000 and 2007 in English and held by 2 WorldCat member libraries worldwide
Phase behavior of dipolar fluids and iondipole mixtures, and surface diffusion of adsorbed polymers by Won Ki Roh(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Dipole moments are ubiquitous in nature. Studying dipole moments is the first step toward understanding phase behavior of various colloids with strong dipole moments. Since the Dipolar Hard Sphere fluid (DHS) is the simplest model described by dipolar interactions, studying this model is fundamentally important for understanding the structures and thermodynamics of polar fluids. A variety of unsolved scientific questions arises when the dimensionality of this model is changed and when other species are introduced in this model. Finally, the last part of this dissertation discusses the diffusion behavior of adsorbed polymers over the full concentration range. In Chapter 2, I study the phase behavior of dipolar fluids by means of Monte Carlo simulations. My goal in this chapter is to examine the possibility of phase separation in a dipolar fluid system and to use quantitative structural information to shed light on this controversy. How dimensionality affects the phase behavior of dipolar fluids is an interesting question. Thus, in Chapter 3, I examine the possibility of phase separation in quasi2D dipolar fluids. In Chapter 4, I proceed to binary systems. Since I have excluded the possibility of phase separation in the DHS system and it is well known that the RPM system exhibits phase separation, these result naturally lead to the question whether phase separation takes place in mixtures that contain ions as well as dipolar particles. I map out the phase diagrams by varying the strength ratio of the dipolar to the ionic interaction and I also locate the critical points. In Chapter 5, I turn to a rather different research topic, namely the dynamics of adsorbed polymers. I employ molecular dynamics to investigate the relation between surface diffusion and conformation of adsorbed polymers over the full coverage range
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Dipole moments are ubiquitous in nature. Studying dipole moments is the first step toward understanding phase behavior of various colloids with strong dipole moments. Since the Dipolar Hard Sphere fluid (DHS) is the simplest model described by dipolar interactions, studying this model is fundamentally important for understanding the structures and thermodynamics of polar fluids. A variety of unsolved scientific questions arises when the dimensionality of this model is changed and when other species are introduced in this model. Finally, the last part of this dissertation discusses the diffusion behavior of adsorbed polymers over the full concentration range. In Chapter 2, I study the phase behavior of dipolar fluids by means of Monte Carlo simulations. My goal in this chapter is to examine the possibility of phase separation in a dipolar fluid system and to use quantitative structural information to shed light on this controversy. How dimensionality affects the phase behavior of dipolar fluids is an interesting question. Thus, in Chapter 3, I examine the possibility of phase separation in quasi2D dipolar fluids. In Chapter 4, I proceed to binary systems. Since I have excluded the possibility of phase separation in the DHS system and it is well known that the RPM system exhibits phase separation, these result naturally lead to the question whether phase separation takes place in mixtures that contain ions as well as dipolar particles. I map out the phase diagrams by varying the strength ratio of the dipolar to the ionic interaction and I also locate the critical points. In Chapter 5, I turn to a rather different research topic, namely the dynamics of adsorbed polymers. I employ molecular dynamics to investigate the relation between surface diffusion and conformation of adsorbed polymers over the full coverage range
Modecoupling theory of the slow dynamics of polymeric liquids fractal macromolecular architectures by
Matthias Fuchs(
)
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
A fast algorithm for approximating hydrodynamic lubrication interactions between elastic particles by Kenneth F Higa(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
We present in this work a fast nonlinear method which approximately solves an integropartial differential equation that describes the dominant elastohydrodynamic lubrication interaction between two elastic spheres in a Newtonian fluid. This governing equation was given by Christensen [7], Goddard [13], and Davis, Serayssol, and Hinch (DSH) [8]. Our approximate method is intended for inclusion in highly accurate, largescale simulations of concentrated suspensions of deformable particles. This method inherits all of the assumptions made in the derivation elastohydrodynamic equation, including the restriction to linearlyelastic deformation of smooth particles in a Newtonian fluid with noslip boundary conditions, and consideration of relative motion only along the axis of symmetry. The approximate solutions are characterized by a variable number of parameters, whose number may be chosen to balance accuracy and speed. This method shows good accuracy and stability over a wide range of conditions. We present selected simulation results which provide a qualitative understanding of hydrodynamic collisions of elastic spheres. These interactions differ markedly from those between rigid spheres. They are strongly dependent on deformation history and display a shortlived "sticking" behavior, which in extreme cases takes the form of a unique "peeling" separation process
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
We present in this work a fast nonlinear method which approximately solves an integropartial differential equation that describes the dominant elastohydrodynamic lubrication interaction between two elastic spheres in a Newtonian fluid. This governing equation was given by Christensen [7], Goddard [13], and Davis, Serayssol, and Hinch (DSH) [8]. Our approximate method is intended for inclusion in highly accurate, largescale simulations of concentrated suspensions of deformable particles. This method inherits all of the assumptions made in the derivation elastohydrodynamic equation, including the restriction to linearlyelastic deformation of smooth particles in a Newtonian fluid with noslip boundary conditions, and consideration of relative motion only along the axis of symmetry. The approximate solutions are characterized by a variable number of parameters, whose number may be chosen to balance accuracy and speed. This method shows good accuracy and stability over a wide range of conditions. We present selected simulation results which provide a qualitative understanding of hydrodynamic collisions of elastic spheres. These interactions differ markedly from those between rigid spheres. They are strongly dependent on deformation history and display a shortlived "sticking" behavior, which in extreme cases takes the form of a unique "peeling" separation process
Microencapsulation of reactive amines and isocyanates and their application to selfhealing systems by David A McIlroy(
)
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Microcapsulebased selfhealing systems enable repair of crack damage in polymers and polymer matrix composites. Existing selfhealing chemistries are limited by relatively weak chemical bonding between the matrix and the healing material, temperature stability, and side reactions that degrade the active components. We demonstrate for the first time a twopart system that incorporates a healing chemistry similar to the matrix curing chemistry, enabling chemical bonding between the healed material and the matrix material. Aminecontaining microcapsules are synthesized by interfacial polymerization of a polyurea about a droplet of amine by means of suspension polymerization. Capsules are subsequently isolated and analyzed for content, and shown to contain reactive amine. The microcapsules containing reactive amine are employed in concert with microcapsules containing epoxy resin to recover fracture toughness in a cured epoxy. Both capsule types are dispersed in an epoxy resin and the resin is chemically cured. Mechanical load is applied to propagate a crack and rupture microcapsules contained within the cured resin. The average peak load at failure in a virgin specimen is recorded, and compared to the average peak load at failure in the same specimen after a healing period. Recovery of fracture toughness is limited to 15% for specimens healed at temperatures of 50 oC and below, whereas healing efficiencies of up to 60% are observed for specimens healed at temperatures above 80 oC. Control specimens where amine was not present failed to recover. Microcapsules containing isocyanate are also prepared by means of interfacial polyurea condensation. These capsules are also isolated and analyzed for content, and shown to contain reactive isocyanate. No healing was observed with these capsules, however, due to problems with bonding and longterm stability. With refinement, the isocyanate system is projected for use in polyurethane matrix materials where a moisturecure could promote the healing reaction
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Microcapsulebased selfhealing systems enable repair of crack damage in polymers and polymer matrix composites. Existing selfhealing chemistries are limited by relatively weak chemical bonding between the matrix and the healing material, temperature stability, and side reactions that degrade the active components. We demonstrate for the first time a twopart system that incorporates a healing chemistry similar to the matrix curing chemistry, enabling chemical bonding between the healed material and the matrix material. Aminecontaining microcapsules are synthesized by interfacial polymerization of a polyurea about a droplet of amine by means of suspension polymerization. Capsules are subsequently isolated and analyzed for content, and shown to contain reactive amine. The microcapsules containing reactive amine are employed in concert with microcapsules containing epoxy resin to recover fracture toughness in a cured epoxy. Both capsule types are dispersed in an epoxy resin and the resin is chemically cured. Mechanical load is applied to propagate a crack and rupture microcapsules contained within the cured resin. The average peak load at failure in a virgin specimen is recorded, and compared to the average peak load at failure in the same specimen after a healing period. Recovery of fracture toughness is limited to 15% for specimens healed at temperatures of 50 oC and below, whereas healing efficiencies of up to 60% are observed for specimens healed at temperatures above 80 oC. Control specimens where amine was not present failed to recover. Microcapsules containing isocyanate are also prepared by means of interfacial polyurea condensation. These capsules are also isolated and analyzed for content, and shown to contain reactive isocyanate. No healing was observed with these capsules, however, due to problems with bonding and longterm stability. With refinement, the isocyanate system is projected for use in polyurethane matrix materials where a moisturecure could promote the healing reaction
Single particle motion of polymeric, colloidal, and biological materials by Stephen M Anthony(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Small particles and their dynamics are of widespread interest due both to their unique properties and their ubiquity. Here, we investigate several classes of small particles: colloids, polymers, and liposomes. All these particles, due to their size on the order of microns, exhibit significant similarity in that they are large enough to be visualized in microscopes, but small enough to be significantly influenced by thermal (or Brownian) motion. Further, similar optical microscopy and experimental techniques are commonly employed to investigate all these particles. In this work, we develop single particle tracking techniques, which allow thorough characterization of individual particle dynamics, observing many behaviors which would be overlooked by methods which time or ensemble average. The various particle systems are also similar in that frequently, the signaltonoise ratio represented a significant concern. In many cases, development of image analysis and particle tracking methods optimized to low signaltonoise was critical to performing experimental observations. The simplest particles studied, in terms of their interaction potentials, were chemically homogeneous (though optically anisotropic) hardsphere colloids. Using these spheres, we explored the comparatively underdeveloped conjunction of translation and rotation and particle hydrodynamics. Developing off this, the dynamics of clusters of spherical colloids were investigated, exploring how shape anisotropy influences the translation and rotation respectively. Transitioning away from uniform hardsphere potentials, the interactions of amphiphilic colloidal particles were explored, observing the effects of hydrophilic and hydrophobic interactions upon pattern assembly and interparticle dynamics. Interaction potentials were altered in a different fashion by working with suspensions of liposomes, which, while homogeneous, introduce the possibility of deformation. Even further degrees of freedom were introduced by observing the interaction of particles and then polymers within polymer suspensions or along lipid tubules. Throughout, while examination of the trajectories revealed that while by some measures, the averaged behaviors accorded with expectation, often closer examination made possible by single particle tracking revealed novel and unexpected phenomena
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Small particles and their dynamics are of widespread interest due both to their unique properties and their ubiquity. Here, we investigate several classes of small particles: colloids, polymers, and liposomes. All these particles, due to their size on the order of microns, exhibit significant similarity in that they are large enough to be visualized in microscopes, but small enough to be significantly influenced by thermal (or Brownian) motion. Further, similar optical microscopy and experimental techniques are commonly employed to investigate all these particles. In this work, we develop single particle tracking techniques, which allow thorough characterization of individual particle dynamics, observing many behaviors which would be overlooked by methods which time or ensemble average. The various particle systems are also similar in that frequently, the signaltonoise ratio represented a significant concern. In many cases, development of image analysis and particle tracking methods optimized to low signaltonoise was critical to performing experimental observations. The simplest particles studied, in terms of their interaction potentials, were chemically homogeneous (though optically anisotropic) hardsphere colloids. Using these spheres, we explored the comparatively underdeveloped conjunction of translation and rotation and particle hydrodynamics. Developing off this, the dynamics of clusters of spherical colloids were investigated, exploring how shape anisotropy influences the translation and rotation respectively. Transitioning away from uniform hardsphere potentials, the interactions of amphiphilic colloidal particles were explored, observing the effects of hydrophilic and hydrophobic interactions upon pattern assembly and interparticle dynamics. Interaction potentials were altered in a different fashion by working with suspensions of liposomes, which, while homogeneous, introduce the possibility of deformation. Even further degrees of freedom were introduced by observing the interaction of particles and then polymers within polymer suspensions or along lipid tubules. Throughout, while examination of the trajectories revealed that while by some measures, the averaged behaviors accorded with expectation, often closer examination made possible by single particle tracking revealed novel and unexpected phenomena
Shape and chemically anisotropic colloidal particles: A theoretical study of their structure, phase behavior, and slow dynamics by Mukta Tripathy(
)
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
A detailed nonequilibrium state diagram of shapeanisotropic particle fluids is constructed. The effects of particle shape are explored using Naive Mode Coupling Theory (NMCT), and a single particle Nonlinear Langevin Equation (NLE) theory. The dynamical behavior of nonergodic fluids are discussed. We employ a rotationally frozen approach to NMCT in order to determine a transition to center of mass (translational) localization. Both ideal and kinetic glass transitions are found to be highly shape dependent, and uniformly increase with particle dimensionality. The glass transition volume fraction of quasi 1 and 2 dimensional particles fall monotonically with the number of sites (aspect ratio), while 3dimensional particles display a nonmonotonic dependence of glassy vitrification on the number of sites. Introducing interparticle attractions results in a far more complex state diagram. The ideal nonergodic boundary shows a glassfluidgel reentrance previously predicted for spherical particle fluids. The nonergodic region of the state diagram presents qualitatively different dynamics in different regimes. They are qualified by the different behaviors of the NLE dynamic free energy. The caging dominated, repulsive glass regime is characterized by long localization lengths and barrier locations, dictated by repulsive hard core interactions, while the bonding dominated gel region has short localization lengths (commensurate with the attraction range), and barrier locations. There exists a small region of the state diagram which is qualified by both glassy and gel localization lengths in the dynamic free energy. A much larger (high volume fraction, and high attraction strength) region of phase space is characterized by short gellike localization lengths, and long barrier locations. The region is called the attractive glass and represents a 2step relaxation process whereby a particle first breaks attractive physical bonds, and then escapes its topological cage. The dynamic fragility of fluids are highly particle shape dependent. It increases with particle dimensionality and falls with aspect ratio for quasi 1 and 2 dimentional particles. An ultralocal limit analysis of the NLE theory predicts universalities in the behavior of relaxation times, and elastic moduli. The equlibrium phase diagram of chemically anisotropic Janus spheres and Janus rods are calculated employing a mean field Random Phase Approximation. The calculations for Janus rods are corroborated by the full liquid state Reference Interaction Site Model theory. The Janus particles consist of attractive and repulsive regions. Both rods and spheres display rich phase behavior. The phase diagrams of these systems display fluid, macrophase separated, attraction driven microphase separated, repulsion driven microphase separated and crystalline regimes. Macrophase separation is predicted in highly attractive low volume fraction systems. Attraction driven microphase separation is charaterized by long length scale divergences, where the ordering length scale determines the microphase ordered structures. The ordering length scale of repulsion driven microphase separation is determined by the repulsive range. At the high volume fractions, particles forgo the enthalpic considerations of attractions and repulsions to satisfy hard core constraints and maximize vibrational entropy. This results in site length scale ordering in rods, and the sphere length scale ordering in Janus spheres, i.e., crystallization. A change in the Janus balance of both rods and spheres results in quantitative changes in spinodal temperatures and the position of phase boundaries. However, a change in the block sequence of Janus rods causes qualitative changes in the type of microphase ordered state, and induces prominent features (such as the Lifshitz point) in the phase diagrams of these systems. A detailed study of the number of nearest neighbors in Janus rod systems reflect a deep connection between this local measure of structure, and the structure factor which represents the most global measure of order
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
A detailed nonequilibrium state diagram of shapeanisotropic particle fluids is constructed. The effects of particle shape are explored using Naive Mode Coupling Theory (NMCT), and a single particle Nonlinear Langevin Equation (NLE) theory. The dynamical behavior of nonergodic fluids are discussed. We employ a rotationally frozen approach to NMCT in order to determine a transition to center of mass (translational) localization. Both ideal and kinetic glass transitions are found to be highly shape dependent, and uniformly increase with particle dimensionality. The glass transition volume fraction of quasi 1 and 2 dimensional particles fall monotonically with the number of sites (aspect ratio), while 3dimensional particles display a nonmonotonic dependence of glassy vitrification on the number of sites. Introducing interparticle attractions results in a far more complex state diagram. The ideal nonergodic boundary shows a glassfluidgel reentrance previously predicted for spherical particle fluids. The nonergodic region of the state diagram presents qualitatively different dynamics in different regimes. They are qualified by the different behaviors of the NLE dynamic free energy. The caging dominated, repulsive glass regime is characterized by long localization lengths and barrier locations, dictated by repulsive hard core interactions, while the bonding dominated gel region has short localization lengths (commensurate with the attraction range), and barrier locations. There exists a small region of the state diagram which is qualified by both glassy and gel localization lengths in the dynamic free energy. A much larger (high volume fraction, and high attraction strength) region of phase space is characterized by short gellike localization lengths, and long barrier locations. The region is called the attractive glass and represents a 2step relaxation process whereby a particle first breaks attractive physical bonds, and then escapes its topological cage. The dynamic fragility of fluids are highly particle shape dependent. It increases with particle dimensionality and falls with aspect ratio for quasi 1 and 2 dimentional particles. An ultralocal limit analysis of the NLE theory predicts universalities in the behavior of relaxation times, and elastic moduli. The equlibrium phase diagram of chemically anisotropic Janus spheres and Janus rods are calculated employing a mean field Random Phase Approximation. The calculations for Janus rods are corroborated by the full liquid state Reference Interaction Site Model theory. The Janus particles consist of attractive and repulsive regions. Both rods and spheres display rich phase behavior. The phase diagrams of these systems display fluid, macrophase separated, attraction driven microphase separated, repulsion driven microphase separated and crystalline regimes. Macrophase separation is predicted in highly attractive low volume fraction systems. Attraction driven microphase separation is charaterized by long length scale divergences, where the ordering length scale determines the microphase ordered structures. The ordering length scale of repulsion driven microphase separation is determined by the repulsive range. At the high volume fractions, particles forgo the enthalpic considerations of attractions and repulsions to satisfy hard core constraints and maximize vibrational entropy. This results in site length scale ordering in rods, and the sphere length scale ordering in Janus spheres, i.e., crystallization. A change in the Janus balance of both rods and spheres results in quantitative changes in spinodal temperatures and the position of phase boundaries. However, a change in the block sequence of Janus rods causes qualitative changes in the type of microphase ordered state, and induces prominent features (such as the Lifshitz point) in the phase diagrams of these systems. A detailed study of the number of nearest neighbors in Janus rod systems reflect a deep connection between this local measure of structure, and the structure factor which represents the most global measure of order
Polymermodecoupling theory of the slow dynamics of entangled macromolecular fluids by Kenneth S Schweizer(
)
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
Statistical mechanical theory of structure and miscibility of polymer nanocomposites: Effects of density, filler shape, and
chemical heterogeneity by
Lisa M Hall(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Motivated by increasing interest in various types of nanoparticles or fillers added to polymers to enhance the material properties, the Polymer Reference Site Interaction Model (PRISM) theory is applied to study the structure and miscibility of polymer nanocomposites (PNCs). Spherical fillers are studied in homopolymers of varying density and interfacial interaction strengths, with specific favorable comparisons to experimental scattering results. Also discussed briefly are copolymers composed of two types of monomer which interact differently with the filler. The polymer induced depletion attraction is dominant and causes phase separation if interfacial attractions are weak. Complete miscibility can be achieved at moderate interfacial attraction strengths, due to a sterically stabilizing bound polymer layer. The bound layer remains with a strong interfacial attraction, but phase separation is induced by polymer bridging between nanoparticles. For copolymers, the bridging attraction is strongly affected by chemistry and monomer spatial arrangement (random versus alternating). The effect of nanoparticle dimensionality is explored by comparing rod, disk, and cube shaped fillers. Nanoparticle interactions on several length scales are relevant in the depletion regime. The bound polymer layer present in the miscible and bridging regimes damps out order on these length scales in favor of increased order on an averaged filler length scale. The effect of nanoparticle chemical heterogeneity was briefly explored by investigation of fillers composed of two tangentially connected spheres with different polymer interfacial attraction strengths or with an added internanoparticle sitesite attraction. Such heterogeneous diatomic fillers exhibited additional structural features and particle clustering compared to analogous homogeneous nanoparticles. Motivated by recent experimental interest in carbon nanotubes, thin rod particles were further investigated. Adding a strong rodrod attraction relevant to nanotubes predictably leads to a strongly attractive potential of mean force at contact, especially when there is little bound polymer. In the stabilized and bridging regimes, miscibility can persist until a stronger rodrod attraction if it is of shorter spatial range than the polymerrod interfacial attraction. An initial investigation of these attractive rods in a random copolymer revealed that replacing the homopolymer with copolymer can significantly reduce miscibility
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Motivated by increasing interest in various types of nanoparticles or fillers added to polymers to enhance the material properties, the Polymer Reference Site Interaction Model (PRISM) theory is applied to study the structure and miscibility of polymer nanocomposites (PNCs). Spherical fillers are studied in homopolymers of varying density and interfacial interaction strengths, with specific favorable comparisons to experimental scattering results. Also discussed briefly are copolymers composed of two types of monomer which interact differently with the filler. The polymer induced depletion attraction is dominant and causes phase separation if interfacial attractions are weak. Complete miscibility can be achieved at moderate interfacial attraction strengths, due to a sterically stabilizing bound polymer layer. The bound layer remains with a strong interfacial attraction, but phase separation is induced by polymer bridging between nanoparticles. For copolymers, the bridging attraction is strongly affected by chemistry and monomer spatial arrangement (random versus alternating). The effect of nanoparticle dimensionality is explored by comparing rod, disk, and cube shaped fillers. Nanoparticle interactions on several length scales are relevant in the depletion regime. The bound polymer layer present in the miscible and bridging regimes damps out order on these length scales in favor of increased order on an averaged filler length scale. The effect of nanoparticle chemical heterogeneity was briefly explored by investigation of fillers composed of two tangentially connected spheres with different polymer interfacial attraction strengths or with an added internanoparticle sitesite attraction. Such heterogeneous diatomic fillers exhibited additional structural features and particle clustering compared to analogous homogeneous nanoparticles. Motivated by recent experimental interest in carbon nanotubes, thin rod particles were further investigated. Adding a strong rodrod attraction relevant to nanotubes predictably leads to a strongly attractive potential of mean force at contact, especially when there is little bound polymer. In the stabilized and bridging regimes, miscibility can persist until a stronger rodrod attraction if it is of shorter spatial range than the polymerrod interfacial attraction. An initial investigation of these attractive rods in a random copolymer revealed that replacing the homopolymer with copolymer can significantly reduce miscibility
Statistical imaging of transport in complex fluids: a journey from entangled polymers to living cells by Bo Wang(
)
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Combining advanced fluorescence imaging, single particle tracking, and quantitative analysis in the framework of statistical mechanics, we studied several transport phenomena in complex fluids with nanometer and millisecond resolution. On the list are diffusion of nanoparticles and vesicles in crowded environments, reptational motion of polymers in entangled semidilute solutions, and active endosome transport along microtubules in living cells. We started from individual trajectories, and then converged statistically to aggregate properties of interests, with special emphasis on the fluctuations buried under the classic meanfield descriptions. The unified scientific theme behind these diversified subjects is to examine, with experiments designed as direct as possible, the commonly believed fundamental assumptions in those fields, such as Gaussian displacements in Fickian diffusion, harmonic confining potential of virtual tubes in polymer entanglements, and bidirectional motion of active intracellular transport. This series of efforts led us to discoveries of new phenomena, mechanisms, and concepts. This route, we termed as ⁰́statistical imaging⁰́₊, is expected to be widely useful at studying dynamic processes, especially in those emerging fields at the overlap of physics and biology
1 edition published in 2011 in English and held by 2 WorldCat member libraries worldwide
Combining advanced fluorescence imaging, single particle tracking, and quantitative analysis in the framework of statistical mechanics, we studied several transport phenomena in complex fluids with nanometer and millisecond resolution. On the list are diffusion of nanoparticles and vesicles in crowded environments, reptational motion of polymers in entangled semidilute solutions, and active endosome transport along microtubules in living cells. We started from individual trajectories, and then converged statistically to aggregate properties of interests, with special emphasis on the fluctuations buried under the classic meanfield descriptions. The unified scientific theme behind these diversified subjects is to examine, with experiments designed as direct as possible, the commonly believed fundamental assumptions in those fields, such as Gaussian displacements in Fickian diffusion, harmonic confining potential of virtual tubes in polymer entanglements, and bidirectional motion of active intracellular transport. This series of efforts led us to discoveries of new phenomena, mechanisms, and concepts. This route, we termed as ⁰́statistical imaging⁰́₊, is expected to be widely useful at studying dynamic processes, especially in those emerging fields at the overlap of physics and biology
Entropy driven phase transitions in colloid polymer suspensions Tests of depletion theories by S Ramakrishnan(
)
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 2002 and 2007 in English and held by 2 WorldCat member libraries worldwide
Microscale dynamics in suspensions of nonspherical particles by Amit Kumar(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Numerical simulations were performed to investigate the microscale dynamics in suspensions of spherical and nonspherical particles. Two new algorithms were developed to enable studies with accurate hydrodynamics. The first algorithm was a high accuracy Stokesian Dynamics technique (SD) extended to a generic nonspherical particle shape. The many body interactions were computed using a novel scheme employing one body singularity solutions. Near field lubrication interactions employed standard asymptotic solutions for nearly touching convex particles. The second algorithm was a reduced precision nearfield lubrication based method called Fast Lubrication Dynamics (FLD). In addition to the near field interactions, we introduced a novel isotropic resistance in FLD to match the mean particle mobility from the more detailed SD. The resulting FLD algorithm was shown to give results comparable to that from the detailed SD, while requiring only a fraction of the latter's computational expense. In a first series of studies using the SD technique, we computed the transport properties in equilibrium suspensions of spheres and dicolloids. The latter particle shape was modeled as two intersecting spheres of varying radii and center to center separations. It was found that the infinite frequency viscosity as well as the shorttime translational selfdiffusivity are nonmonotonic function of aspect ratio at any given nondilute volume fraction with the minima in viscosity and the maxima in selfdiffusivity around an aspect of 1.5. In contrast, the shorttime rotational selfdiffusivity was found to be a monotonically decreasing function of the aspect ratio at any given volume fraction. In a second series of studies using the SD technique we investigated the microstructure, orientation, and rheology in suspensions of spheres and dicolloids over a wide range of volume fractions $0 leq phi leq 0.55$. The particles had a very short range repulsive interparticle interaction. The microstructure in suspensions of all particle shapes was found to be disordered for volume fractions $phi leq 0.5$, while a string like ordering was observed in suspensions of spheres and other particles with small degree of anisotropy at $phi=0.55$. Both the first and the second normal stress differences were negative for volume fractions up to $phi=0.5$, but some were positive at the highest volume fraction studied here ($phi=0.55$). The orientation behavior was found to be a function of both the foreaft symmetry and the degree of anisotropy. For particles with foreaft symmetry, in comparison to infinite dilution, a shift to higher orbit constants (increased alignment in the flowgradient plane) was observed at low volume fractions. On the other hand, the particle lacking foreaft symmetry showed virtually no change in its orientation distribution at low volume fractions. At higher volume fractions ($phi geq 0.2$), in comparison to the dilute suspensions, a shift towards lower orbit constants (increased alignment with the vorticity axis) was observed for all particle shapes. The degree of this alignment was found to increase with volume fraction for particles with small degree of anisotropy, while it was found to plateau at relatively low volume fractions in suspensions of particles with the largest degree of anisotropy. The observed orientation behavior was explained using a novel analysis technique based on the coupling of particle's angular velocity and hydrodynamic stresslet through the mobility tensor. Next, we investigated microstructure and orientation in Brownian suspensions of spheres and dicolloids using the FLD algorithm. Results are reported for two different volume fractions, $phi=42%$ and $phi=55%$. The 42% sample had a long range repulsive electrostatic interaction, while the 55% sample had hardsphere type interaction. Particles with small degree of anisotropy showed microstructural transitions similar to that of spheres. In contrast, particles with relatively larger degree of anisotropy showed a significantly different microstructural behavior. At low shear rates, irrespective of the degree of anisotropy, an orientationally disordered state was observed. Upon further increase in the rate of shear, an increase in flow alignment is obtained, with the maximum flow alignment typically observed between $Pe=1$ and $Pe=20$ depending on the particle shape. With a further increase in the rate of shear, an increase in vorticity alignment is seen for all particle shapes. The degree of anisotropy and volume fraction was found to have a significant impact on the extent of increase in the flow or the vorticity alignment. Using FLD simulations we next investigated the phase behavior and rheology in charged colloidal suspensions at a volume fraction of $phi=0.33$. It was shown that for a given screening length of the repulsive interaction, there existed a range of surface potentials for which both the ordered and disordered metastable states exist. This range was found to have a strong dependence on shear rate and was found to have a maximum width around $Pe = 0.5$, where $Pe = dot{gamma}a^2/D_0$. The presence of both the ordered and disordered metastable states allowed us to simultaneously characterize both the branches of viscosity as a function of shear rate. It was observed that the disordered branch can have a lower viscosity than the ordered branch at low shear rates ($Pe <0.05$ in this study). This was attributed to the much smaller longtime selfdiffusivity in the ordered state, which leads to a greater distortion of the microstructure and hence stress at the same shear rate. At higher shear rates, on the other hand, ordered states with close packed planes aligned in the flowvorticity direction were able to minimize the distortive effects of shear, and hence have lower viscosities than the corresponding disordered states. The microstructural dynamics revealed in these studies explains the anomalous behavior and hysteresis loops in stress data reported in the literature. In a last series of studies using the FLD algorithm, we investigated the shear thickening phenomena in suspensions of spheres. Using a short range repulsive force to control the gapsize in a shearing suspension, it was shown that the suspension viscosity has a much weaker logarithmic dependence on the minimum gap size present in the suspension. This dependence of the viscosity on the minimum gap size was shown to persist even at volume fractions as high as $phi=0.62$. This study poses intriguing questions about the origins of discontinuous shear thickening in these systems which is commonly observed in experiments
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
Numerical simulations were performed to investigate the microscale dynamics in suspensions of spherical and nonspherical particles. Two new algorithms were developed to enable studies with accurate hydrodynamics. The first algorithm was a high accuracy Stokesian Dynamics technique (SD) extended to a generic nonspherical particle shape. The many body interactions were computed using a novel scheme employing one body singularity solutions. Near field lubrication interactions employed standard asymptotic solutions for nearly touching convex particles. The second algorithm was a reduced precision nearfield lubrication based method called Fast Lubrication Dynamics (FLD). In addition to the near field interactions, we introduced a novel isotropic resistance in FLD to match the mean particle mobility from the more detailed SD. The resulting FLD algorithm was shown to give results comparable to that from the detailed SD, while requiring only a fraction of the latter's computational expense. In a first series of studies using the SD technique, we computed the transport properties in equilibrium suspensions of spheres and dicolloids. The latter particle shape was modeled as two intersecting spheres of varying radii and center to center separations. It was found that the infinite frequency viscosity as well as the shorttime translational selfdiffusivity are nonmonotonic function of aspect ratio at any given nondilute volume fraction with the minima in viscosity and the maxima in selfdiffusivity around an aspect of 1.5. In contrast, the shorttime rotational selfdiffusivity was found to be a monotonically decreasing function of the aspect ratio at any given volume fraction. In a second series of studies using the SD technique we investigated the microstructure, orientation, and rheology in suspensions of spheres and dicolloids over a wide range of volume fractions $0 leq phi leq 0.55$. The particles had a very short range repulsive interparticle interaction. The microstructure in suspensions of all particle shapes was found to be disordered for volume fractions $phi leq 0.5$, while a string like ordering was observed in suspensions of spheres and other particles with small degree of anisotropy at $phi=0.55$. Both the first and the second normal stress differences were negative for volume fractions up to $phi=0.5$, but some were positive at the highest volume fraction studied here ($phi=0.55$). The orientation behavior was found to be a function of both the foreaft symmetry and the degree of anisotropy. For particles with foreaft symmetry, in comparison to infinite dilution, a shift to higher orbit constants (increased alignment in the flowgradient plane) was observed at low volume fractions. On the other hand, the particle lacking foreaft symmetry showed virtually no change in its orientation distribution at low volume fractions. At higher volume fractions ($phi geq 0.2$), in comparison to the dilute suspensions, a shift towards lower orbit constants (increased alignment with the vorticity axis) was observed for all particle shapes. The degree of this alignment was found to increase with volume fraction for particles with small degree of anisotropy, while it was found to plateau at relatively low volume fractions in suspensions of particles with the largest degree of anisotropy. The observed orientation behavior was explained using a novel analysis technique based on the coupling of particle's angular velocity and hydrodynamic stresslet through the mobility tensor. Next, we investigated microstructure and orientation in Brownian suspensions of spheres and dicolloids using the FLD algorithm. Results are reported for two different volume fractions, $phi=42%$ and $phi=55%$. The 42% sample had a long range repulsive electrostatic interaction, while the 55% sample had hardsphere type interaction. Particles with small degree of anisotropy showed microstructural transitions similar to that of spheres. In contrast, particles with relatively larger degree of anisotropy showed a significantly different microstructural behavior. At low shear rates, irrespective of the degree of anisotropy, an orientationally disordered state was observed. Upon further increase in the rate of shear, an increase in flow alignment is obtained, with the maximum flow alignment typically observed between $Pe=1$ and $Pe=20$ depending on the particle shape. With a further increase in the rate of shear, an increase in vorticity alignment is seen for all particle shapes. The degree of anisotropy and volume fraction was found to have a significant impact on the extent of increase in the flow or the vorticity alignment. Using FLD simulations we next investigated the phase behavior and rheology in charged colloidal suspensions at a volume fraction of $phi=0.33$. It was shown that for a given screening length of the repulsive interaction, there existed a range of surface potentials for which both the ordered and disordered metastable states exist. This range was found to have a strong dependence on shear rate and was found to have a maximum width around $Pe = 0.5$, where $Pe = dot{gamma}a^2/D_0$. The presence of both the ordered and disordered metastable states allowed us to simultaneously characterize both the branches of viscosity as a function of shear rate. It was observed that the disordered branch can have a lower viscosity than the ordered branch at low shear rates ($Pe <0.05$ in this study). This was attributed to the much smaller longtime selfdiffusivity in the ordered state, which leads to a greater distortion of the microstructure and hence stress at the same shear rate. At higher shear rates, on the other hand, ordered states with close packed planes aligned in the flowvorticity direction were able to minimize the distortive effects of shear, and hence have lower viscosities than the corresponding disordered states. The microstructural dynamics revealed in these studies explains the anomalous behavior and hysteresis loops in stress data reported in the literature. In a last series of studies using the FLD algorithm, we investigated the shear thickening phenomena in suspensions of spheres. Using a short range repulsive force to control the gapsize in a shearing suspension, it was shown that the suspension viscosity has a much weaker logarithmic dependence on the minimum gap size present in the suspension. This dependence of the viscosity on the minimum gap size was shown to persist even at volume fractions as high as $phi=0.62$. This study poses intriguing questions about the origins of discontinuous shear thickening in these systems which is commonly observed in experiments
Structural properties and phase behavior in colloidal suspensions by Stephen Austin Barr(
)
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
In this dissertation I present my research on the effective interactions of colloidal particles induced by a smaller species, as well as the structure of colloidal particles undergoing freeze casting. In this research I have used a wide variety of computational techniques in order to understand these systems. Specifically, in Chapter 2 I study nanoparticle haloing in a system of silica microspheres and highly charged polystyrene nanoparticles. Computer simulations are employed to determine the effective microsphere⁰́₃ microsphere potential induced by the nanoparticles. From these simulations I am also able to determine the degree of nanoparticle adsorption on the microsphere surface. In Chapter 3 I investigate the depletion interaction in a system of charged microspheres and rigid rods. The effect of both rod concentration and screening length is explored. In Chapter 4 I study the effective interactions between charged colloids in the presence of multivalent counterions. The role of colloid charge is investigated and the onset of likecharged attraction is determined and compared with theoretical predictions. In order to study this system, I extended the geometric cluster algorithm to efficiently simulate systems interacting through the Coulomb potential. In Chapter 5 computer simulations are employed to elucidate the experimentally observed crystal phases of the Q and MS2 virus particles in solution with multivalent salt and nonadsorbing polymer. Freeze casting is studied in Chapter 6. In this process colloidal particles are pushed by an advancing ice front. I use molecular dynamics simulations to study the dynamics of the colloidal particles and the resulting structures formed. iii
1 edition published in 2010 in English and held by 2 WorldCat member libraries worldwide
In this dissertation I present my research on the effective interactions of colloidal particles induced by a smaller species, as well as the structure of colloidal particles undergoing freeze casting. In this research I have used a wide variety of computational techniques in order to understand these systems. Specifically, in Chapter 2 I study nanoparticle haloing in a system of silica microspheres and highly charged polystyrene nanoparticles. Computer simulations are employed to determine the effective microsphere⁰́₃ microsphere potential induced by the nanoparticles. From these simulations I am also able to determine the degree of nanoparticle adsorption on the microsphere surface. In Chapter 3 I investigate the depletion interaction in a system of charged microspheres and rigid rods. The effect of both rod concentration and screening length is explored. In Chapter 4 I study the effective interactions between charged colloids in the presence of multivalent counterions. The role of colloid charge is investigated and the onset of likecharged attraction is determined and compared with theoretical predictions. In order to study this system, I extended the geometric cluster algorithm to efficiently simulate systems interacting through the Coulomb potential. In Chapter 5 computer simulations are employed to elucidate the experimentally observed crystal phases of the Q and MS2 virus particles in solution with multivalent salt and nonadsorbing polymer. Freeze casting is studied in Chapter 6. In this process colloidal particles are pushed by an advancing ice front. I use molecular dynamics simulations to study the dynamics of the colloidal particles and the resulting structures formed. iii
PolymerModeCoupling Theory of FiniteSizeFluctuation Effects in Entangled Solutions, Melts, and Gels. 1. General Formulation
and Predictions by
Matthias Fuchs(
)
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
2 editions published between 1997 and 2007 in English and held by 2 WorldCat member libraries worldwide
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