Colloidal Hydrodynamics at a Fluid-Fluid Interface

The self assembly of colloids at a fluid/fluid interface is a balance between different forces of interest. These typically include interactions because of particle shape and weight (capillary attraction), surface charge (electrostatic repulsions) and viscous dissipative forces which stem from relative motion between the particles and the adjoining fluids. As the particle size decreases from millimeter to colloidal scale, thermal forces and electrostatic interactions play a greater role in affecting the self assembly into ordered patterns and crystal structures. Such self-assembly processes, which initiate at the microscale are the starting point for different types of novel materials.
In this work, simulations involving two particles are implemented to describe the lateral organization of particles along the surface in regimes that includes capillary attraction of a monopolar and quadrupolar nature, electrostatic repulsion of dipolar nature, the hydrodynamic interaction between particles (incorporating the effect of the particle immersion depth) and thermal fluctuations. Clustering is observed at critically large values of the Péclet numbers, while smaller values exhibit higher probabilities of yielding states in which particles remain uncorrelated in space and more widely separated.