Measuring the dispersion relation of capillary waves using differential dynamic microscopy

With a recently-developed method for measuring capillary wave dynamics at the interface of fluids we examine non-equilibrium interfacial fluctuations. We use a colloidal-polymer mixture that separates into colloid-rich and colloid-poor fluid phases with an ultra-low surface tension and capillary velocities on the order of a micron per second. We use differential dynamic microscopy (DDM) to measure the two-dimensional dispersion relation of capillary waves at spatial frequencies spanning over an order of magnitude. Using temperature-responsive colloidal particles (pNIPAM) to tune the phase diagram we investigate the interfacial fluctuations between non-equilibrium phases.