Effective interactions of colloids on nematic films

TL;DR

This paper theoretically investigates the elastic and capillary interactions between colloids on nematic films, revealing that both interactions are predominantly repulsive and decay as the fifth power of separation, with finite thickness effects introducing weak attractions.

Contribution

It provides a detailed theoretical analysis of colloid interactions on nematic films, including the effects of finite film thickness on capillary forces, which was not previously characterized.

Findings

Elastic quadrupolar interactions decay as d^{-5}

Capillary interactions are also repulsive and decay as d^{-5} for thick films

Finite film thickness introduces weak logarithmic capillary attractions

Abstract

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations $d$. The elastic interaction is repulsive and of quadrupolar type, varying as $d^{-5}$. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to $d^{-5}$ as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern formation of colloidal droplets on nematic films.