Experimental study of critical casimir forces on microparticles in critical binary liquid mixtures

Long-ranged forces between mesoscopic objects emerge when a fluctuating field is confined. Analogously to the well known quantum-electro-dynamical (QED) Casimir forces, emerging between conducting objects due to the confinement of the vacuum electromagnetic fluctuations, critical Casimir forces emerge between objects due to confinement of the fluid density fluctuations. Here, we studied experimentally several novel aspects and applications of critical Casimir fluctuations in a critical mixture of walter-2,6-lutidine, which are a promising candidate to harness forces and interactions at mesoscopic and nanoscopic lengthscales and promise to deliver results of both fundamental and applied interest. In particular, we studied the critical Casimir forces between multiple objects and multiple-body effects. We first extended the experimental study of critical Casimir forces in configurations different from the particle-wall system[1]. The forces acting between two particles in far from any surface and the third particle effect were explored. Then we employed multiple reconfigurable holographic optical tweezers (HOTs) which permit to optically trap several colloids and used a technique known as ”digital video microscopy” (DVM) to track the particles’ trajectories and the forces acting on the particles. We studied the critical Casimir force arising between two particles as a function of their distance and investigated how this is affected by the presence of a third neighboring particle.