Lattice Boltzmann simulations of soft matter systems

This article concerns numerical simulations of the dynamics of particles immersed in a continuum solvent. As prototypical systems, we consider colloidal dispersions of spherical particles and solutions of uncharged polymers. After a brief explanation of the concept of hydrodynamic interactions, we give a general overview over the various simulation methods that have been developed to cope with the resulting computational problems. We then focus on the approach we have developed, which couples a system of particles to a lattice Boltzmann model representing the solvent degrees of freedom. The standard D3Q19 lattice Boltzmann model is derived and explained in depth, followed by a detailed discussion of complementary methods for the coupling of solvent and solute. Colloidal dispersions are best described in terms of extended particles with appropriate boundary conditions at the surfaces, while particles with internal degrees of freedom are easier to simulate as an arrangement of mass points with frictional coupling to the solvent. In both cases, particular care has been taken to simulate thermal fluctuations in a consistent way. The usefulness of this methodology is illustrated by studies from our own research, where the dynamics of colloidal and polymeric systems has been investigated in both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures, 76 page

Modified Bautista–Manero (MBM) modelling for hyperbolic contraction–expansion flows

In this study, modelling of network-structured material flow is considered through a rounded-corner, hyperbolic 4:1:4 contraction-expansion geometry, under axisymmetric configuration. Three representative constitutive models are adopted to represent networked behaviour and to investigate the flow of wormlike micellar fluids in this context. This includes the MBM model (for base thixotropic properties), some newly proposed micellar models (NM_τp & NM_T; for advanced thixotropic modelling), and the EPPT model (for contrast against non-thixotropic properties). In this configuration, emphasis is placed upon interpretation of flow behaviour for these constitutive models, against their response in simple rheometrical flows. To best determine the factors that contribute to epd-prediction, current findings have also been contrasted against those reported earlier in Lopez-Aguilar et al. [1], for the counterpart abrupt rounded-corner, axisymmetric 4:1:4 contraction-expansion flow