Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence o... more Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence of a microstructure on multiple length scales, which is sensitive to flow and flow history.
Since decades, most porous polymeric membranes are prepared via phase inversion. It allows the fo... more Since decades, most porous polymeric membranes are prepared via phase inversion. It allows the formation of a variety of porous structures, but in spite of all research, it remains difficult to control the porosity of the membrane. Emulsion templating is an interesting alternative to prepare ordered macroporous membranes. In the mid eighties Barby and Haq introduced this principle in the preparation of porous polymers [1].
In inertialess suspensions of rigid particles, the rotational motion of each particle is governed... more In inertialess suspensions of rigid particles, the rotational motion of each particle is governed by the so-called freely rotating condition, whereby the total torque acting on the particle must be zero. In this work, we study the effect of viscoelasticity of the suspending liquid on the rotation period of a sphere by means of three-dimensional finite element simulations, for conditions corresponding to a macroscopic shear flow.
The magnetic interfacial needle stress rheometer is a device capable of sensitive rheological int... more The magnetic interfacial needle stress rheometer is a device capable of sensitive rheological interfacial measurements. Yet even for this device, when measuring interfaces with low elastic and viscous moduli, the system response of the instrument contributes significantly to the measured response. To determine the operation limits of the magnetic rod rheometer, we analyze the relative errors that are introduced by linearly subtracting the instrument contribution from the measured response.
The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene part... more The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed. While undisturbed, the particles arrange themselves on a hexagonal lattice due to strong dipole–dipole repulsion resulting from ionizable sulfate groups on their surfaces. As the interface is subjected to shear flow, however, the lattice adopts a new semi-ordered, anisotropic state for which two distinct regimes are observed.
ABSTRACT: When particles are dispersed in viscoelastic rather than Newtonian media, the hydrodyna... more ABSTRACT: When particles are dispersed in viscoelastic rather than Newtonian media, the hydrodynamics will be changed entailing differences in suspension rheology. The disturbance velocity profiles and stress distributions around the particle will depend on the viscoelastic material functions. Even in inertialess flows, changes in particle rotation and migration will occur.
Bacterial swarming is one of the most efficient methods by which bacteria colonize nutrient-rich ... more Bacterial swarming is one of the most efficient methods by which bacteria colonize nutrient-rich environments and host tissues. Several mechanisms have been proposed to explain the phenomenon and the associated intricate macroscopic pattern formation, but so far no conclusive evidence has been presented that identifies the factors that control swarming. Vice versa, little is known about how swarming can be controlled.
The synthesis and selected macroscopic properties of a new model system consisting of poly (N-iso... more The synthesis and selected macroscopic properties of a new model system consisting of poly (N-isopropylacrylamide)(PNIPAM)-coated rod-like fd virus particles are presented. The sticky rod-like colloids can be used to study effect of particle shape on gelation transition, the structure and viscoelasticity of isotropic and nematic gels, and to make both open isotropic as well as ordered nematic particle networks.
Particle shape plays an important role in controlling the optical, magnetic, and mechanical prope... more Particle shape plays an important role in controlling the optical, magnetic, and mechanical properties of nanoparticle suspensions as well as nanocomposites. However, character-izing the size, shape, and the associated polydispersity of nanoparticles is not straightforward. Electron microscopy provides an accurate measurement of the geometric properties, but sample preparation can be laborious, and to obtain statistically relevant data many particles need to be analyzed separately.
Rheological measurements are used to compare clay nanocomposites prepared through melt mixing usi... more Rheological measurements are used to compare clay nanocomposites prepared through melt mixing using two different polypropylene matrices. Steady state and transient nonlinear rheological experiments are employed to separate the contributions of flow induced orientation of the tactoids and particulate network build-up. The conditions under which the rheological properties are dominated by the aggregate network are subsequently identified.
Synopsis The effect of a delicate balance of forces on the interparticle dynamics and structure o... more Synopsis The effect of a delicate balance of forces on the interparticle dynamics and structure of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed as shear flow was applied to the system. A strong dipole–dipole repulsion, due to ionizable surface sulfate groups, induces the particles to arrange themselves on a hexagonal lattice under quiescent conditions.
The origin of the nonlinearity observed in Bagley plots of thermotropic copolyesters has been inv... more The origin of the nonlinearity observed in Bagley plots of thermotropic copolyesters has been investigated experimentally. With the aid of a two-piston slit rheometer the dependence of the viscosity on the hydrostatic pressure has been determined directly. This dependence only accounts for part of the nonlinearity of the Bagley plots. Using slit dies with either a convergent or a divergent entrance, concave as well as convex pressure profiles are obtained.
Flow small-angle light scattering and linear conservative dichroism are used to follow, in situ a... more Flow small-angle light scattering and linear conservative dichroism are used to follow, in situ and time resolved, the flow-induced changes of the microstructure in viscous emulsions such as immiscible polymer blends. A dilute system consisting of poly (butadiene) droplets dispersed in a poly (isobutene) matrix has been used as a model system. Contrary to earlier rheo-optical work on such materials, the structure has been probed in the plane formed by the flow and the velocity gradient directions.
Steric stabilization is a method that is often used to properly disperse small particles. It can ... more Steric stabilization is a method that is often used to properly disperse small particles. It can be applied in aqueous as well as non-aqueous media. The rheological properties of sterically stabilized dispersions are discussed here. The various controlling parameters and the physical mechanisms involved are reviewed. Brownian hard spheres are used as a reference. Scaling relations are presented that make it possible to reduce data sets and to predict properties.
Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colon... more Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells. Here, we provide a review of recent advances in the study of the regulatory pathways that lead to swarming behavior of different model bacteria.
Abstract We review the sequences of structural states that can be induced in colloidal suspension... more Abstract We review the sequences of structural states that can be induced in colloidal suspensions by the application of flow. Structure formation during flow is strongly affected by the delicate balance among interparticle forces, Brownian motion and hydrodynamic interactions. The resulting nonequilibrium microstructure is in turn a principal determinant of the suspension rheology. Colloidal suspensions with near hard-sphere interactions develop an anisotropic, amorphous structure at low dimensionless shear rates.
Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the sur... more Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces.
Abstract Swarming motility is suggested to be a social phenomenon that enables groups of bacteria... more Abstract Swarming motility is suggested to be a social phenomenon that enables groups of bacteria to coordinately and rapidly move atop solid surfaces. This multicellular behavior, during which the apparently organized bacterial populations are embedded in an extracellular slime layer, has previously been linked with biofilm formation and virulence. Many population density-controlled activities involve the activation of complex signaling pathways using small diffusible molecules, also known as autoinducers.
Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence o... more Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence of a microstructure on multiple length scales, which is sensitive to flow and flow history.
Since decades, most porous polymeric membranes are prepared via phase inversion. It allows the fo... more Since decades, most porous polymeric membranes are prepared via phase inversion. It allows the formation of a variety of porous structures, but in spite of all research, it remains difficult to control the porosity of the membrane. Emulsion templating is an interesting alternative to prepare ordered macroporous membranes. In the mid eighties Barby and Haq introduced this principle in the preparation of porous polymers [1].
In inertialess suspensions of rigid particles, the rotational motion of each particle is governed... more In inertialess suspensions of rigid particles, the rotational motion of each particle is governed by the so-called freely rotating condition, whereby the total torque acting on the particle must be zero. In this work, we study the effect of viscoelasticity of the suspending liquid on the rotation period of a sphere by means of three-dimensional finite element simulations, for conditions corresponding to a macroscopic shear flow.
The magnetic interfacial needle stress rheometer is a device capable of sensitive rheological int... more The magnetic interfacial needle stress rheometer is a device capable of sensitive rheological interfacial measurements. Yet even for this device, when measuring interfaces with low elastic and viscous moduli, the system response of the instrument contributes significantly to the measured response. To determine the operation limits of the magnetic rod rheometer, we analyze the relative errors that are introduced by linearly subtracting the instrument contribution from the measured response.
The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene part... more The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed. While undisturbed, the particles arrange themselves on a hexagonal lattice due to strong dipole–dipole repulsion resulting from ionizable sulfate groups on their surfaces. As the interface is subjected to shear flow, however, the lattice adopts a new semi-ordered, anisotropic state for which two distinct regimes are observed.
ABSTRACT: When particles are dispersed in viscoelastic rather than Newtonian media, the hydrodyna... more ABSTRACT: When particles are dispersed in viscoelastic rather than Newtonian media, the hydrodynamics will be changed entailing differences in suspension rheology. The disturbance velocity profiles and stress distributions around the particle will depend on the viscoelastic material functions. Even in inertialess flows, changes in particle rotation and migration will occur.
Bacterial swarming is one of the most efficient methods by which bacteria colonize nutrient-rich ... more Bacterial swarming is one of the most efficient methods by which bacteria colonize nutrient-rich environments and host tissues. Several mechanisms have been proposed to explain the phenomenon and the associated intricate macroscopic pattern formation, but so far no conclusive evidence has been presented that identifies the factors that control swarming. Vice versa, little is known about how swarming can be controlled.
The synthesis and selected macroscopic properties of a new model system consisting of poly (N-iso... more The synthesis and selected macroscopic properties of a new model system consisting of poly (N-isopropylacrylamide)(PNIPAM)-coated rod-like fd virus particles are presented. The sticky rod-like colloids can be used to study effect of particle shape on gelation transition, the structure and viscoelasticity of isotropic and nematic gels, and to make both open isotropic as well as ordered nematic particle networks.
Particle shape plays an important role in controlling the optical, magnetic, and mechanical prope... more Particle shape plays an important role in controlling the optical, magnetic, and mechanical properties of nanoparticle suspensions as well as nanocomposites. However, character-izing the size, shape, and the associated polydispersity of nanoparticles is not straightforward. Electron microscopy provides an accurate measurement of the geometric properties, but sample preparation can be laborious, and to obtain statistically relevant data many particles need to be analyzed separately.
Rheological measurements are used to compare clay nanocomposites prepared through melt mixing usi... more Rheological measurements are used to compare clay nanocomposites prepared through melt mixing using two different polypropylene matrices. Steady state and transient nonlinear rheological experiments are employed to separate the contributions of flow induced orientation of the tactoids and particulate network build-up. The conditions under which the rheological properties are dominated by the aggregate network are subsequently identified.
Synopsis The effect of a delicate balance of forces on the interparticle dynamics and structure o... more Synopsis The effect of a delicate balance of forces on the interparticle dynamics and structure of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed as shear flow was applied to the system. A strong dipole–dipole repulsion, due to ionizable surface sulfate groups, induces the particles to arrange themselves on a hexagonal lattice under quiescent conditions.
The origin of the nonlinearity observed in Bagley plots of thermotropic copolyesters has been inv... more The origin of the nonlinearity observed in Bagley plots of thermotropic copolyesters has been investigated experimentally. With the aid of a two-piston slit rheometer the dependence of the viscosity on the hydrostatic pressure has been determined directly. This dependence only accounts for part of the nonlinearity of the Bagley plots. Using slit dies with either a convergent or a divergent entrance, concave as well as convex pressure profiles are obtained.
Flow small-angle light scattering and linear conservative dichroism are used to follow, in situ a... more Flow small-angle light scattering and linear conservative dichroism are used to follow, in situ and time resolved, the flow-induced changes of the microstructure in viscous emulsions such as immiscible polymer blends. A dilute system consisting of poly (butadiene) droplets dispersed in a poly (isobutene) matrix has been used as a model system. Contrary to earlier rheo-optical work on such materials, the structure has been probed in the plane formed by the flow and the velocity gradient directions.
Steric stabilization is a method that is often used to properly disperse small particles. It can ... more Steric stabilization is a method that is often used to properly disperse small particles. It can be applied in aqueous as well as non-aqueous media. The rheological properties of sterically stabilized dispersions are discussed here. The various controlling parameters and the physical mechanisms involved are reviewed. Brownian hard spheres are used as a reference. Scaling relations are presented that make it possible to reduce data sets and to predict properties.
Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colon... more Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells. Here, we provide a review of recent advances in the study of the regulatory pathways that lead to swarming behavior of different model bacteria.
Abstract We review the sequences of structural states that can be induced in colloidal suspension... more Abstract We review the sequences of structural states that can be induced in colloidal suspensions by the application of flow. Structure formation during flow is strongly affected by the delicate balance among interparticle forces, Brownian motion and hydrodynamic interactions. The resulting nonequilibrium microstructure is in turn a principal determinant of the suspension rheology. Colloidal suspensions with near hard-sphere interactions develop an anisotropic, amorphous structure at low dimensionless shear rates.
Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the sur... more Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces.
Abstract Swarming motility is suggested to be a social phenomenon that enables groups of bacteria... more Abstract Swarming motility is suggested to be a social phenomenon that enables groups of bacteria to coordinately and rapidly move atop solid surfaces. This multicellular behavior, during which the apparently organized bacterial populations are embedded in an extracellular slime layer, has previously been linked with biofilm formation and virulence. Many population density-controlled activities involve the activation of complex signaling pathways using small diffusible molecules, also known as autoinducers.
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Papers by Jan Vermant