Solvent coarsening around laser-heated colloids and related effective forces

Laser illuminating a Janus colloid which is suspended in a near-critical binary solvent leads to the formation of the concentration gradient and coarsening patterns around the colloid, which leads to its phoretic motion. Using analytical theory and numerical simulations, we investigate this non-equilibrium phenomenon under the influence of a time-dependent temperature gradient. Our predictions are also confirmed by experiments with Gold-capped Janus particles immersed in PnP-water binary liquid mixture. Time-dependent properties of the coarsening patterns for various surface adsorption properties of the Janus colloid are analyzed. We also present results for structure formation around colloidal particles kept confined in thin films with confining surfaces preferring one species of the binary liquid mixture over the other. Confinement leads to the formation of a bridge connecting the colloid and both the confining walls. It is observed that the particle starts to move much before the stationary state is achieved. Results will also be presented on the time-dependent effective interactions between two such heated colloidal particles.