Controlling the dynamics of colloidal particles by critical Casimir forces

TL;DR

This study explores how critical Casimir forces influence the motion of colloidal particles in a near-critical liquid, using optical tweezers and comparing experimental results with simulations to understand their dynamic behavior.

Contribution

It provides experimental measurements of colloidal dynamics under critical Casimir forces and validates theoretical models with empirical data.

Findings

Critical Casimir forces affect colloidal diffusion and drift.

Temperature modulates the first-passage time distribution.

Experimental results agree with Monte Carlo and Langevin simulations.

Abstract

Critical Casimir forces can play an important role for applications in nano-science and nanotechnology, owing to their piconewton strength, nanometric action range, fine tunability as a function of temperature, and exquisite dependence on the surface properties of the involved objects. Here, we investigate the effects of critical Casimir forces on the free dynamics of a pair of colloidal particles dispersed in the bulk of a near-critical binary liquid solvent, using blinking optical tweezers. In particular we measure the time evolution of the distance between the two colloids to determine their relative diffusion and drift velocity. Furthermore, we show how critical Casimir forces change the dynamic properties of this two-colloid system by studying the temperature dependence of the distribution of the so-called first-passage time, i.e., of the time necessary for the particles to reach for the first time a certain separation, starting from an initially assigned one. These data are in good agreement with theoretical results obtained from Monte Carlo simulations and Langevin dynamics.