Alladi Ramakrishnan Hall

Self-propulsion by Marangoni forces

Venkata Sathish Akella

IIT Madras

We experimentally study the self-propulsion of particles/drops induced by surface tension gradients also known as Marangoni forces. In the first part of the talk, we report experiments on an agarose gel tablet loaded with camphoric acid (c-boat) spontaneously set into motion by surface tension gradients on the water surface. We observe three distinct modes of c-boat motion: harmonic mode where the c-boat speed oscillates sinusoidally in time, a steady mode where the c-boat maintains constant speed, and an intermittent mode where the c-boat maintains near-zero speed between sudden jumps in speed. Whereas all three modes have been separately reported before in different systems, controlled release of camphoric acid from the agarose gel matrix allowed the observation of all the three modes in the same system. In the second part, we report self-propulsion of liquid drops on a liquid surface. The dynamics invovled are quite rich in comparison to that of a particle on liquid surface as a liquid drop exhibits motion, deformation and break up. In this regard, we experimentally study the motion of an Octanoic Acid drop on aqueous solutions of octanoic acid. In the current work, we study a regime where triple line undulations result in varying Marangoni propulsion and a random walking drop. We discuss two parametric regimes where the drop motion exhibits a Levy walk and a near-Gaussian random walk. We present mean squared displacement, probability distributions of step lengths as well as from velocity auto-correlations from observations of the drop motion as evidence. Finally, we show that the drop `foraging' mimics a living system.