Journal of Chemical Physics 132, 124906-124916, (2010).
Dynamic Simulations of colloids by core-modified dissipative particle dynamics.
Martin Whittle and Karl P. Travis.
Abstract:
We develop a core-modified dissipative particle dynamics model of colloidal systems
that includes an extra term to counteract depletion forces. Results are presented
covering the full range of volume fractions. Radial distribution functions for the
suspending fluid are shown to change significantly as the volume fraction of colloid
increases. Equilibrium results for the long-time diffusion coefficient behave as
expected, but the short-time coefficient is anomalous. The form of the equilibrium
stress correlation functions is discussed and the derived Green-Kubo viscosities are
compared with expected semi-empirical forms. For non-equilibrium shear-field
simulations we find that the system temperature is not adequately controlled by the
DPD thermostat alone. Results using three alternative auxiliary thermostats are
compared; a naïve choice leading to a string phase at high shear rate. Using a
thermostat based on relative particle velocities the model reproduced the four classical
regions of colloid rheology: a first Newtonian plateau, a shear-thinning region, a
second Newtonian plateau and finally a shear-thickening region at high strain rate.
The most unexpected result of this exercise is that the core-modified DPD model
without auxiliary thermostat almost exactly follows the same curve despite recording
a temperature increase of a factor ~2.5 over the range.