Abstract
In the thesis we report on simulations of the nonlinear rheology of coreshell sytsems. The coreshell system is a model for resins to be used in novel water borne coating systems. Resin particles can be considered as a hard spheres, grafted with soft, in water soluble, polymeric coronas. A new Brownian dynamics model is presented to describe the coarse grain dynamics of these particles with longlived memory. Instead of solving a set of generalised Langevin equations we introduce a set of variable describing the slowly fluctuating thermodynamic state of the ignored degrees of freedom. These variables give rise to additional transient forces on the simulated particles.
The parameters in the model are tuned to represent experimental shear thinning data of resin systems correctly. Increasing the influence of the transient forces results in shear banding. In a well defined range of imposed shear rates, the system settles in a banded state with two coexisting bands stacked along the gradient direction. Both bands have the same symmetry but differ in shear rate and density. Additional, the influence of other model parameters on the rheology is studied. Continuous planar elongation flow is implsed in the simulation. The measured elongational viscosity as a function of the deformation rate is compared to the shear viscosity. Using superposition we studied the response of a sheared system to a perturbation causing a flow in the vorticity direction with a gradient in the direction of the shear flow. For low shear rates, the viscosity measured from the perturbation agrees with the shear viscosity, at higher shear rates a deviation is observed.
As an application we studied the string formation of colloids dissolved in a strong shear thinning solvent. The solvent is modelled by the newly developed resin model. Starting from a random configuration the simulated colloids are seen to align in stringlike structures, in agreement with experimental observations.
The parameters in the model are tuned to represent experimental shear thinning data of resin systems correctly. Increasing the influence of the transient forces results in shear banding. In a well defined range of imposed shear rates, the system settles in a banded state with two coexisting bands stacked along the gradient direction. Both bands have the same symmetry but differ in shear rate and density. Additional, the influence of other model parameters on the rheology is studied. Continuous planar elongation flow is implsed in the simulation. The measured elongational viscosity as a function of the deformation rate is compared to the shear viscosity. Using superposition we studied the response of a sheared system to a perturbation causing a flow in the vorticity direction with a gradient in the direction of the shear flow. For low shear rates, the viscosity measured from the perturbation agrees with the shear viscosity, at higher shear rates a deviation is observed.
As an application we studied the string formation of colloids dissolved in a strong shear thinning solvent. The solvent is modelled by the newly developed resin model. Starting from a random configuration the simulated colloids are seen to align in stringlike structures, in agreement with experimental observations.
Original language  English 

Qualification  Doctor of Philosophy 
Awarding Institution 

Supervisors/Advisors 

Award date  6 Jul 2007 
Place of Publication  Enschede 
Publisher  
Print ISBNs  9789036525206 
Publication status  Published  6 Jul 2007 
Keywords
 METIS241217