Simulation study of a colloidal system under the influence of an external electric field.

摘要

We perform Monte Carlo simulations to study an electrorheological fluid that consists of spherical dielectric particles in a solution of low dielectric constant under the influence of an external electric field. The electric field induces dipole moments in the colloids that align along to the electric field direction. At a sufficiently high electric field, the dipoles attract each other to form long chains along the electric field direction. The system can then be modeled as a 2D system of interacting disks, where each disk represents a chain of hard sphere dipolar particles viewed along the field axis. The disk-disk interaction varies with chain length, but has the general feature of strong short range attraction and weak long range repulsion. We perform simulations of the 2D fluid across a wide range of temperature and area fraction to study its structural properties and phase behaviour. Our model reproduces the clustered structures seen experimentally;In addition, a novel void phase has been seen by two experimental groups in a low volume fraction regime (1%). The simulations of our model indicate that dipolar hard spheres, even with the addition of Yukawa and van der Waals interactions, do not produce the void phase. Further investigations employing toy potentials reveal qualitative features of the potential that can give rise to voids, but physical mechanisms that may produce these features remain speculative.