Chaotic motion of microplugs under high-frequency thermocapillary actuation.

Abstract

This paper reports experimental results on chaotic motion of liquid plugs under high-frequency thermocapillary actuation. In the experiments, two heaters were alternately activated. The liquid plug was positioned in a glass capillary between these two heaters. The periodic temperature gradients generated by the two heaters made the liquid plug move back and forth. The images of the plug were captured by a camera. Plug position by a customized image-processing programme. The results were recorded as time series for further analysis. The nonlinear motion of the liquid plug in a glass capillary was systematically investigated with tools coming from chaotic dynamics. Phase-space portraits are reconstructed from the time series of the plug position obtained in the experiments. The results show that the limit sets formed by the phase-space trajectories are attractors. The largest Lyapunov exponent and correlation dimension of these attractors are calculated and indicate that these attractors are chaotic. A chaotic plug motion has potential applications in fluid mixing inside liquid plugs of capillary-based microfluidics. External chaotic motion could improve mixing in liquid plugs of capillary-based lab-on-a-chip platforms.