Rheology, Microstructure and Migration in Brownian Colloidal Suspensions

Abstract

We demonstrate that suspended spherical colloidal particles can be effectively modeled as single dissipative particle dynamics (DPD) particles provided that the conservative repulsive force is appropriately chosen. The suspension model is further improved with a new formulation, which augments standard DPD with noncentral dissipative shear forces between particles while preserving angular momentum. Using the new DPD formulation we investigate the rheology, microstructure and shear-induced migration of a monodisperse suspension of colloidal particles in plane shear flows (Couette and Poiseuille). Specifically, to achieve a well-dispersed suspension we employ exponential conservative forces for the colloid-colloid and colloid-solvent interactions but keep the conventional linear force for the solvent-solvent interactions. Our simulations yield relative viscosity versus volume fraction predictions in good agreement with both experimental data and empirical correlations. We also compute the shear-dependent viscosity and the first and second normal-stress differences and coefficients in both Couette and Poiseuille flow. Simulations near the close packingvolume-fraction (64%) at low shear rates demonstrate a transition to flow-induced string-like structures of colloidal particles simultaneously with a transition to a nonlinear Couette velocity profile in agreement with experimental observations. After a sufficient increase ofthe shear rate the ordered structure melts into disorder with restoration of the linear velocity profile. Migration effects simulated in Poiseuille flow compare well with experiments and model predictions. The important role of angular momentum and torque in nondilute suspensions is also demonstrated when compared with simulations by the standard DPD, which omits the angular degrees of freedom. Overall, the new method agrees very well with the Stokesian Dynamics method but it seems to have lower computational complexity and is applicable to general complex fluids systems.

Strongly overdamped Dissipative Particle Dynamics for fluid-solid systems

“…A suspended particle of spherical/circular shape can be modelled using a single DPD particle [15][16][17][18][19]8] or a set of frozen DPD particles [20][21][22][23]. The single particle model involves three groups of DPD parameters: the first group associated with the interactions between solventsolvent particles, the second with solvent-colloidal particles and the third with colloidalcolloidal particles.…”

A dissipative particle dynamics model for thixotropic materials exhibiting pseudo-yield stress behaviour

“…Many applications of DPD method 75 or its variants in the simulations of complex fluids have been reported, e.g., sphere colloidal suspensions ( [15]; [16]; [17]; [18]; [19]; [20]), colloidal suspensions of spheres, rods, and disks [21], viscoelastic fluid [22], ferromagnetic colloidal suspension [23], magnetic colloidal dispersions [24], soft matter and polymeric applications [25], [26], lipid bilayer [27], flows of DNA suspensions [28], poly-80 mer chains [29], red blood cell modelling [30], [31]; this list is not meant to be exhaustive.…”

A spring model for suspended particles in dissipative particle dynamics

“…In [Pan et al (2010a)], for SC and CC interactions, the conservative force is taken as a steep exponential potential. Such a steep form for the conservative force was deemed necessary to produce a uniform colloidal dispersion [Pan et al (2010a) ]. Stokes results are then utilised to determine the strength of the dissipative forces.…”