(469b) Osmophoretic Motion of Semipermeable Polymersomes Driven By Solute Gradients in Microfluidic Channels

Gradients in the osmotic pressure difference across the semipermeable membrane of a polymersome result in fluid flows, which direct osmophoretic motion to regions of lower concentration. The previous osmophoretic velocity measurements of DMPC lipid membrane was four orders of magnitude larger than the model predicted velocity. We find the existence of circulating buoyancy-driven flows due to density difference at two boundaries when external concentration gradients are applied. Such flows exhibit velocities comparable to those due to osmophoresis but are overlooked in previous studies. To mitigate the buoyancy-driven flows, we prepare the high and low concentration sources with two different solutes, such as sucrose and glucose to balance the density. With the same density, glucose solution has a higher concentration than sucrose solution, which create sugar concentration gradients in the microfluidic system but avoid the buoyancy-driven flows. Based on the model proposed by John Anderson, a 10 µm in radius lipid membrane in a 1 mM/µm gradient should move toward the lower concentration side with a 0.01 µm/s velocity, which is still hard to measure experimentally. We then fabricate high water permeable tens of micron-sized polymersomes from water/oil/water double emulsions and quantify the enhanced osmophoretic velocity in the density matching sugar gradients.