Hans Wyss | Eindhoven University of Technology (original) (raw)

Papers by Hans Wyss

Macromolecules, 2017

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures ... more We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of = 0.15-0.35. Our systems are density-matched, residual charges are a͒

Physical Review Letters

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

ABSTRACT Conventional wisdom dictates that studying the mechanical response of viscoelastic mater... more ABSTRACT Conventional wisdom dictates that studying the mechanical response of viscoelastic materials in the nonlinear regime should be done either with a cone-plate or a Couette geometry, where the applied strain is homogenous in the measuring volume. However, the use of parallel plates would have important advantages in a wide range of applications. For instance solid-like hydrogel materials can often be processed readily into flat films. We show that the nonlinear viscoelastic behavior can also be obtained from measurements in a parallel plate geometry. By tracing the torque response and its derivative with respect to the applied strain, we obtain a general stress strain relation, which indeed captures the proper material behavior. The approach does not require any assumptions for the material's viscoelastic behavior. We show practical examples different classes of soft materials to illustrate that our approach enables access to the full nonlinear response of these materials, including the detailed shape of the stress response in large amplitude oscillatory shear measurements. Our approach should be applicable to a wide range of soft materials, including hydrogels, colloidal suspensions, or biological tissues.

Key Engineering …, 2002

... concentrations up to 0.05mol/l added salt (Fig. 3c). The micrograph of the sample a with salt... more ... concentrations up to 0.05mol/l added salt (Fig. 3c). The micrograph of the sample a with salt additions of 0.1 mol/l is comparable to that sample with 40 minutes Idle Time (Fig.3d). A crack-free structure was achieved by the addition ...

Using diffusing-wave spectroscopy, we followed the aggregation and gelation of concentrated (30 v... more Using diffusing-wave spectroscopy, we followed the aggregation and gelation of concentrated (30 vol%) alumina suspensions. The suspensions were destabilized by either shifting the pH to the iso-electric point or by increasing the ionic strength. Both effects can be achieved continuously and homogeneously by using an enzyme-catalyzed internal chemical reaction. Based on the light-scattering data, we could derive quantitative information about the sol–gel transition and the viscoelastic properties of the gels, as well as a characterization of changes in the microstructure. The elastic mod-uli determined from light scattering are found to be in good agreement with rheological measurements. C 2001 Academic Press

Git Laboratory Journal Europe, 2007

Aps Meeting Abstracts, 2004

Strongly attractive colloids can form gels even at very low volume fractions. However, under the ... more Strongly attractive colloids can form gels even at very low volume fractions. However, under the influence of gravity, the stability of the network is limited by its rheological properties. The network collapses until its local yield stress is greater than the gravitational stress exerted by the mass of the network. The dynamics of the collapse exhibit unusual behavior depending on system size and volume fraction of solids. For high volume fractions and thick cells, the gel height drops exponentially with time. By contrast, for low volume fractions and thin cells, after an initial slow collapse, the gel undergoes significant restructuring, leading to fluidization and rapid sedimentation. We explore the dependence of network collapse on cell dimensions, and its implications on the rheological properties of colloidal gels.

Interactions between surfaces and particles in aqueous suspension are usually limited to distance... more Interactions between surfaces and particles in aqueous suspension are usually limited to distances smaller than 1 μm. However, in a range of studies from different disciplines, repulsion of particles has been observed over distances of up to hundreds of micrometers, in the absence of any additional external fields. Although a range of hypotheses have been suggested to account for such behavior, the physical mechanisms responsible for the phenomenon still remain unclear. To identify and isolate these mechanisms, we perform detailed experiments on a well-defined experimental system, using a setup that minimizes the effects of gravity and convection. Our experiments clearly indicate that the observed long-range repulsion is driven by a combination of ion exchange, ion diffusion, and diffusiophoresis. We develop a simple model that accounts for our data; this description is expected to be directly applicable to a wide range of systems exhibiting similar long-range forces. exclusion zone | Nafion | chemotaxis | unstirred layer | solute-free zone E xclusion zone (EZ) formation is a phenomenon where colloidal particles in an aqueous suspension are repelled from an interface over distances of up to hundreds of micrometers, leading to the formation of a particle-free zone in the vicinity of the interface. Such peculiar behavior has been observed by researchers from different disciplines for a wide range of materials, including biological tissues such as rabbit cornea (1), white blood cells (2), polymer gels (3), ion-exchange membranes (4), or metals (5). Depending on the field of research, different terms have been used to refer to the behavior. In biological systems, already in the early 1970s, EZs observed close to the surface of biological tissues such as stratum corneum were referred to as unstirred layers (1), as these colloid-free layers persisted even when the suspensions were stirred. In later studies, the formation of similar EZs, where Indian ink particles were excluded from the vicinity of leukocyte cells , was referred to as aureole formation.

Suspensions of soft deformable particles are encountered in a wide range of food and biological m... more Suspensions of soft deformable particles are encountered in a wide range of food and biological materials. Examples are biological cells, micelles, vesicles or microgel particles. While the behavior of suspenions of hard spheres - the classical model system of colloid science - is reasonably well understood, a full understanding of these soft particle suspensions remains elusive. The relation between single particle properties and macroscopic mechanical behavior still remains poorly understood in these materials. Here we examine the surprising shear thinning behavior that is observed in soft particle suspensions as a function of particle softness. We use poly-N-isopropylacrylamide (p-NIPAM) microgel particles as a model system to study this effect in detail. These soft spheres show significant shear thinning even at very large Peclet numbers, where this would not be observed for hard particles. The degree of shear thinning is directly related to the single particle elastic propertie...

We use 3D confocal microscopy to understand the packing dynamics and structure of fluorescently l... more We use 3D confocal microscopy to understand the packing dynamics and structure of fluorescently labeled p(NIPAm-co-AAc) microgel colloidal particles. Such systems respond to changes in temperature, pH, and polymer content by changing size, morphology, and interaction behavior. We conduct experiments to understand this behavior in detail: our results show that the dynamics are dominated by attraction driven crystallization and concentration at low pH and concentration only at high pH. Crystal nucleation occurs homogeneously in the suspensions and does not appear to be restricted to geometric boundaries. The growth of crystals is nucleation-limited and can complete on the order of hours. Structural analysis of the crystals formed indicates that the stacking style is insensitive to charge, concentration, size, and stiffness of the particles and remains FCC.

Journal of Physics Condensed Matter

We use 3D confocal microscopy combined with image analysis and particle tracking techniques to st... more We use 3D confocal microscopy combined with image analysis and particle tracking techniques to study the structure and dynamics of aqueous suspensions of fluorescently labelled p(NIPAm-co-AAc) microgel particles. By adjusting the pH we can tune the interactions between the microgel particles from purely repulsive near neutral pH, to weakly attractive at low pH. This change in the interaction potential has a pronounced effect on the manner in which the suspensions solidify. We directly follow the evolution of the system after a quench from the liquid state to obtain detailed information on the route to kinetic arrest. At low pH and low concentration, dynamic arrest results mainly from crystallization driven by the attraction between particles; crystal nucleation occurs homogeneously throughout the sample and does not appear to be localized to geometric boundaries. Moreover, the growth of crystals is characterized by nucleation-limited kinetics where a rapid growth of crystal domains ...

Proceedings of the National Academy of Sciences, 2014

Interactions between surfaces and particles in aqueous suspension are usually limited to distance... more Interactions between surfaces and particles in aqueous suspension are usually limited to distances smaller than 1 μm. However, in a range of studies from different disciplines, repulsion of particles has been observed over distances of up to hundreds of micrometers, in the absence of any additional external fields. Although a range of hypotheses have been suggested to account for such behavior, the physical mechanisms responsible for the phenomenon still remain unclear. To identify and isolate these mechanisms, we perform detailed experiments on a well-defined experimental system, using a setup that minimizes the effects of gravity and convection. Our experiments clearly indicate that the observed long-range repulsion is driven by a combination of ion exchange, ion diffusion, and diffusiophoresis. We develop a simple model that accounts for our data; this description is expected to be directly applicable to a wide range of systems exhibiting similar long-range forces. exclusion zone | Nafion | chemotaxis | unstirred layer | solute-free zone E xclusion zone (EZ) formation is a phenomenon where colloidal particles in an aqueous suspension are repelled from an interface over distances of up to hundreds of micrometers, leading to the formation of a particle-free zone in the vicinity of the interface. Such peculiar behavior has been observed by researchers from different disciplines for a wide range of materials, including biological tissues such as rabbit cornea (1), white blood cells (2), polymer gels (3), ion-exchange membranes (4), or metals (5). Depending on the field of research, different terms have been used to refer to the behavior. In biological systems, already in the early 1970s, EZs observed close to the surface of biological tissues such as stratum corneum were referred to as unstirred layers (1), as these colloid-free layers persisted even when the suspensions were stirred. In later studies, the formation of similar EZs, where Indian ink particles were excluded from the vicinity of leukocyte cells , was referred to as aureole formation.

Europhysics Letters (EPL), 2006

Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoel... more Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoelasticity with increasing oscillatory-strain amplitude; the storage modulus decreases monotonically as the strain amplitude increases whereas the loss modulus has a distinct peak before it decreases at larger strains. We present a qualitative argument to explain this ubiquitous behavior and use mode-coupling theory (MCT) to confirm it. We compare theoretical predictions to the measured nonlinear viscoelasticity in a dense hard-sphere colloidal suspension; reasonable agreement is obtained. The argument given here can be used to obtain new information about linear viscoelasticity of metastable complex fluids from nonlinear strain measurements.

APS Meeting …, 2004

We study a weakly-attractive colloidal suspension at constant volume fraction phi=0.15, in which ... more We study a weakly-attractive colloidal suspension at constant volume fraction phi=0.15, in which the magnitude of the attraction can by controlled by varying the concentration of a non-adsorbing polymer. Strikingly, we observe two distinct transitions: a structural transition at lower ...

We study a colloidal suspension with weak long-range attractions at several volume fractions rang... more We study a colloidal suspension with weak long-range attractions at several volume fractions ranging from phi=0.15\phi=0.15phi=0.15 to phi=0.35\phi=0.35phi=0.35. The magnitude of the attraction is controlled by varying the concentration of a non-adsorbing polymer. At the lowest interaction energies, the ...

AJP: Cell Physiology, 2011

Faraday Discussions, 2012

A dynamic two-scale model is developed that describes the stationary and transient mechanical beh... more A dynamic two-scale model is developed that describes the stationary and transient mechanical behavior of concentrated suspensions made of highly porous particles. Particularly, we are interested in particles that not only deform elastically, but also can swell or shrink by taking up or expelling the viscous solvent from their interior, leading to rate-dependent deformability of the particles. The fine level of the model describes the evolution of particle centers and their current sizes, while the shapes are at present not taken into account. The versatility of the model permits inclusion of density- and temperature-dependent particle interactions, and hydrodynamic interactions, as well as to implement insight into the mechanism of swelling and shrinking. The coarse level of the model is given in terms of macroscopic hydrodynamics. The two levels are mutually coupled, since the flow changes the particle configuration, while in turn the configuration gives rise to stress contributions, that eventually determine the macroscopic mechanical properties of the suspension. Using a thermodynamic procedure for the model development, it is demonstrated that the driving forces for position change and for size change are derived from the same potential energy. The model is translated into a form that is suitable for particle-based Brownian dynamics simulations for performing rheological tests. Various possibilities for connection with experiments, e.g. rheological and structural, are discussed.

AIChE Journal, 2005

Published online in Wiley InterScience (www.interscience.wiley.com).

Macromolecules, 2017

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures ... more We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of = 0.15-0.35. Our systems are density-matched, residual charges are a͒

Physical Review Letters

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

ABSTRACT Conventional wisdom dictates that studying the mechanical response of viscoelastic mater... more ABSTRACT Conventional wisdom dictates that studying the mechanical response of viscoelastic materials in the nonlinear regime should be done either with a cone-plate or a Couette geometry, where the applied strain is homogenous in the measuring volume. However, the use of parallel plates would have important advantages in a wide range of applications. For instance solid-like hydrogel materials can often be processed readily into flat films. We show that the nonlinear viscoelastic behavior can also be obtained from measurements in a parallel plate geometry. By tracing the torque response and its derivative with respect to the applied strain, we obtain a general stress strain relation, which indeed captures the proper material behavior. The approach does not require any assumptions for the material's viscoelastic behavior. We show practical examples different classes of soft materials to illustrate that our approach enables access to the full nonlinear response of these materials, including the detailed shape of the stress response in large amplitude oscillatory shear measurements. Our approach should be applicable to a wide range of soft materials, including hydrogels, colloidal suspensions, or biological tissues.

Key Engineering …, 2002

... concentrations up to 0.05mol/l added salt (Fig. 3c). The micrograph of the sample a with salt... more ... concentrations up to 0.05mol/l added salt (Fig. 3c). The micrograph of the sample a with salt additions of 0.1 mol/l is comparable to that sample with 40 minutes Idle Time (Fig.3d). A crack-free structure was achieved by the addition ...

Using diffusing-wave spectroscopy, we followed the aggregation and gelation of concentrated (30 v... more Using diffusing-wave spectroscopy, we followed the aggregation and gelation of concentrated (30 vol%) alumina suspensions. The suspensions were destabilized by either shifting the pH to the iso-electric point or by increasing the ionic strength. Both effects can be achieved continuously and homogeneously by using an enzyme-catalyzed internal chemical reaction. Based on the light-scattering data, we could derive quantitative information about the sol–gel transition and the viscoelastic properties of the gels, as well as a characterization of changes in the microstructure. The elastic mod-uli determined from light scattering are found to be in good agreement with rheological measurements. C 2001 Academic Press

Git Laboratory Journal Europe, 2007

Aps Meeting Abstracts, 2004

Strongly attractive colloids can form gels even at very low volume fractions. However, under the ... more Strongly attractive colloids can form gels even at very low volume fractions. However, under the influence of gravity, the stability of the network is limited by its rheological properties. The network collapses until its local yield stress is greater than the gravitational stress exerted by the mass of the network. The dynamics of the collapse exhibit unusual behavior depending on system size and volume fraction of solids. For high volume fractions and thick cells, the gel height drops exponentially with time. By contrast, for low volume fractions and thin cells, after an initial slow collapse, the gel undergoes significant restructuring, leading to fluidization and rapid sedimentation. We explore the dependence of network collapse on cell dimensions, and its implications on the rheological properties of colloidal gels.

Interactions between surfaces and particles in aqueous suspension are usually limited to distance... more Interactions between surfaces and particles in aqueous suspension are usually limited to distances smaller than 1 μm. However, in a range of studies from different disciplines, repulsion of particles has been observed over distances of up to hundreds of micrometers, in the absence of any additional external fields. Although a range of hypotheses have been suggested to account for such behavior, the physical mechanisms responsible for the phenomenon still remain unclear. To identify and isolate these mechanisms, we perform detailed experiments on a well-defined experimental system, using a setup that minimizes the effects of gravity and convection. Our experiments clearly indicate that the observed long-range repulsion is driven by a combination of ion exchange, ion diffusion, and diffusiophoresis. We develop a simple model that accounts for our data; this description is expected to be directly applicable to a wide range of systems exhibiting similar long-range forces. exclusion zone | Nafion | chemotaxis | unstirred layer | solute-free zone E xclusion zone (EZ) formation is a phenomenon where colloidal particles in an aqueous suspension are repelled from an interface over distances of up to hundreds of micrometers, leading to the formation of a particle-free zone in the vicinity of the interface. Such peculiar behavior has been observed by researchers from different disciplines for a wide range of materials, including biological tissues such as rabbit cornea (1), white blood cells (2), polymer gels (3), ion-exchange membranes (4), or metals (5). Depending on the field of research, different terms have been used to refer to the behavior. In biological systems, already in the early 1970s, EZs observed close to the surface of biological tissues such as stratum corneum were referred to as unstirred layers (1), as these colloid-free layers persisted even when the suspensions were stirred. In later studies, the formation of similar EZs, where Indian ink particles were excluded from the vicinity of leukocyte cells , was referred to as aureole formation.

Suspensions of soft deformable particles are encountered in a wide range of food and biological m... more Suspensions of soft deformable particles are encountered in a wide range of food and biological materials. Examples are biological cells, micelles, vesicles or microgel particles. While the behavior of suspenions of hard spheres - the classical model system of colloid science - is reasonably well understood, a full understanding of these soft particle suspensions remains elusive. The relation between single particle properties and macroscopic mechanical behavior still remains poorly understood in these materials. Here we examine the surprising shear thinning behavior that is observed in soft particle suspensions as a function of particle softness. We use poly-N-isopropylacrylamide (p-NIPAM) microgel particles as a model system to study this effect in detail. These soft spheres show significant shear thinning even at very large Peclet numbers, where this would not be observed for hard particles. The degree of shear thinning is directly related to the single particle elastic propertie...

We use 3D confocal microscopy to understand the packing dynamics and structure of fluorescently l... more We use 3D confocal microscopy to understand the packing dynamics and structure of fluorescently labeled p(NIPAm-co-AAc) microgel colloidal particles. Such systems respond to changes in temperature, pH, and polymer content by changing size, morphology, and interaction behavior. We conduct experiments to understand this behavior in detail: our results show that the dynamics are dominated by attraction driven crystallization and concentration at low pH and concentration only at high pH. Crystal nucleation occurs homogeneously in the suspensions and does not appear to be restricted to geometric boundaries. The growth of crystals is nucleation-limited and can complete on the order of hours. Structural analysis of the crystals formed indicates that the stacking style is insensitive to charge, concentration, size, and stiffness of the particles and remains FCC.

Journal of Physics Condensed Matter

We use 3D confocal microscopy combined with image analysis and particle tracking techniques to st... more We use 3D confocal microscopy combined with image analysis and particle tracking techniques to study the structure and dynamics of aqueous suspensions of fluorescently labelled p(NIPAm-co-AAc) microgel particles. By adjusting the pH we can tune the interactions between the microgel particles from purely repulsive near neutral pH, to weakly attractive at low pH. This change in the interaction potential has a pronounced effect on the manner in which the suspensions solidify. We directly follow the evolution of the system after a quench from the liquid state to obtain detailed information on the route to kinetic arrest. At low pH and low concentration, dynamic arrest results mainly from crystallization driven by the attraction between particles; crystal nucleation occurs homogeneously throughout the sample and does not appear to be localized to geometric boundaries. Moreover, the growth of crystals is characterized by nucleation-limited kinetics where a rapid growth of crystal domains ...

Proceedings of the National Academy of Sciences, 2014

Interactions between surfaces and particles in aqueous suspension are usually limited to distance... more Interactions between surfaces and particles in aqueous suspension are usually limited to distances smaller than 1 μm. However, in a range of studies from different disciplines, repulsion of particles has been observed over distances of up to hundreds of micrometers, in the absence of any additional external fields. Although a range of hypotheses have been suggested to account for such behavior, the physical mechanisms responsible for the phenomenon still remain unclear. To identify and isolate these mechanisms, we perform detailed experiments on a well-defined experimental system, using a setup that minimizes the effects of gravity and convection. Our experiments clearly indicate that the observed long-range repulsion is driven by a combination of ion exchange, ion diffusion, and diffusiophoresis. We develop a simple model that accounts for our data; this description is expected to be directly applicable to a wide range of systems exhibiting similar long-range forces. exclusion zone | Nafion | chemotaxis | unstirred layer | solute-free zone E xclusion zone (EZ) formation is a phenomenon where colloidal particles in an aqueous suspension are repelled from an interface over distances of up to hundreds of micrometers, leading to the formation of a particle-free zone in the vicinity of the interface. Such peculiar behavior has been observed by researchers from different disciplines for a wide range of materials, including biological tissues such as rabbit cornea (1), white blood cells (2), polymer gels (3), ion-exchange membranes (4), or metals (5). Depending on the field of research, different terms have been used to refer to the behavior. In biological systems, already in the early 1970s, EZs observed close to the surface of biological tissues such as stratum corneum were referred to as unstirred layers (1), as these colloid-free layers persisted even when the suspensions were stirred. In later studies, the formation of similar EZs, where Indian ink particles were excluded from the vicinity of leukocyte cells , was referred to as aureole formation.

Europhysics Letters (EPL), 2006

Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoel... more Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoelasticity with increasing oscillatory-strain amplitude; the storage modulus decreases monotonically as the strain amplitude increases whereas the loss modulus has a distinct peak before it decreases at larger strains. We present a qualitative argument to explain this ubiquitous behavior and use mode-coupling theory (MCT) to confirm it. We compare theoretical predictions to the measured nonlinear viscoelasticity in a dense hard-sphere colloidal suspension; reasonable agreement is obtained. The argument given here can be used to obtain new information about linear viscoelasticity of metastable complex fluids from nonlinear strain measurements.

APS Meeting …, 2004

We study a weakly-attractive colloidal suspension at constant volume fraction phi=0.15, in which ... more We study a weakly-attractive colloidal suspension at constant volume fraction phi=0.15, in which the magnitude of the attraction can by controlled by varying the concentration of a non-adsorbing polymer. Strikingly, we observe two distinct transitions: a structural transition at lower ...

We study a colloidal suspension with weak long-range attractions at several volume fractions rang... more We study a colloidal suspension with weak long-range attractions at several volume fractions ranging from phi=0.15\phi=0.15phi=0.15 to phi=0.35\phi=0.35phi=0.35. The magnitude of the attraction is controlled by varying the concentration of a non-adsorbing polymer. At the lowest interaction energies, the ...

AJP: Cell Physiology, 2011

Faraday Discussions, 2012

A dynamic two-scale model is developed that describes the stationary and transient mechanical beh... more A dynamic two-scale model is developed that describes the stationary and transient mechanical behavior of concentrated suspensions made of highly porous particles. Particularly, we are interested in particles that not only deform elastically, but also can swell or shrink by taking up or expelling the viscous solvent from their interior, leading to rate-dependent deformability of the particles. The fine level of the model describes the evolution of particle centers and their current sizes, while the shapes are at present not taken into account. The versatility of the model permits inclusion of density- and temperature-dependent particle interactions, and hydrodynamic interactions, as well as to implement insight into the mechanism of swelling and shrinking. The coarse level of the model is given in terms of macroscopic hydrodynamics. The two levels are mutually coupled, since the flow changes the particle configuration, while in turn the configuration gives rise to stress contributions, that eventually determine the macroscopic mechanical properties of the suspension. Using a thermodynamic procedure for the model development, it is demonstrated that the driving forces for position change and for size change are derived from the same potential energy. The model is translated into a form that is suitable for particle-based Brownian dynamics simulations for performing rheological tests. Various possibilities for connection with experiments, e.g. rheological and structural, are discussed.

AIChE Journal, 2005

Published online in Wiley InterScience (www.interscience.wiley.com).