Understanding Particle Accumulation Structures (PAS) in Thermocapillary Liquid Bridges

Particle accumulation structures (PAS) in liquid bridges are considered in a didactic approach. After reviewing the experimental results on PAS we explain PAS as a limit cycle of the particle motion in the frame of reference co-rotating with the hydrothermal wave. The limit cycles representing PAS are created by perturbations of the motion of perfect tracer particles. Therefore, the topology of the underlying incompressible flow field is of key importance. Perturbation by particle-free-surface collisions as well as by a density mismatch between particle and liquid are discussed. It is argued that for typical experimental parameters the effect of particle-free-surface collisions leads to formation times compatible with the experimental results while inertial effects are much slower.