Dynamics of the Self-Propelled Motion of a Polymer Solvent Droplet

In this project I investigate the dynamics of the self-propelled motion of a polymer solvent droplet. Similar movement has been witnessed in a variety of situations. For example oil placed on glass substrate coated with Stearyl Trimethyl Ammonium ions exhibits this motion due to the chemical Marangoni effect. Here the droplet absorbs the hydrophobic molecules on the substrate leaving an absence of them behind and and excess in front creating the difference in surface tension[1]. This has also been witnessed during the melting of solid layers of alkenes into droplets. The droplets then move across the surface in a self avoiding path consuming the solid alkene, leaving behind a widening groove[2]. Though there are similarities between these and our situation, current research has not been done to explain the dynamics of this polymer solvent situation. This motion is produced when a droplet of polymer solvent is placed on the surface of the non-solvent bath. This phenomenon was discovered experimentally by Marshall Bremer in the spring of 2006 while attempting to create circular polymer membranes. He performed multiple experiments to determine the cause of this motion. He looked at the action of the solvent when placed on the surface, finding that it quickly spread across the surface but just as quickly disappeared possibly by diffusion or evaporation. He also investigated the dilution of the non-solvent with solvent, finding that this cause the droplet to slow and become more sporadic. From these experiments he speculated that the movement of the droplet was most likely caused by the spreading of the layer of solvent underneath the droplet to areas which have a lower density of the solvent. I want to investigate the motion of this droplet in a fluid dynamic simulation using the lattice Boltzmann algorithm. I hope to determine the mechanism by which these droplets the motion of the droplets is driven[3].