Pre-submission Thesis Presentation

The study of individual and collective dynamics of micron-sized swimmers is of fundamental interest in non-equilibrium soft-matter physics. In recent years various types of artificial microswimmers have been found and their motion is being studied. The artificial microswimmers are relatively simple and can be exploited to study the mechanism of swimming more systematically. Recently, it has been observed that a micron-sized droplet of some liquid when dispersed in a micellar surfactant solution exhibits self-propulsive motion. This thesis deals with the theoretical and experimental studies of such self-propelling liquid crystal droplets in a micellar solution. First, we develop a minimal model that directly correlates the onset of selfpropulsion beyond a total bulk concentration of the surfactant and shows that self-propulsion can be achieved through interfacial processes alone. Using a combination of linear stability analysis and numerical methods we show the existence of a sharp threshold excess surfactant concentration beyond which self-propulsion can occur. Next, we describe the experimental studies on the self-propulsion of isolated liquid crystal droplets suspended in a micellar solution in a quasi-two-dimensional geometry. For a fixed surfactant concentration and temperature, it was found that by increasing the radius of the droplets, the characteristic motion changes from directed → self-avoiding-random walk (SRW)→ random walk (RW). For even larger droplets, we found that the droplets showed considerable deformation of the apparent cross-section as viewed from above during their motion. Finally, we describe our experimental studies on the scattering of a pair of droplets depending on their size and initial conditions. Four different types of scattering processes for acute and obtuse angles of approach of the droplets were observed in our system. The existence of bound states for larger droplets has also been found in our system.