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Capillary driven thin film dynamics — case studies of dewetting and capillary levelling for multilayer coextrusion and polymeric slip
In the study of capillary-driven fluid dynamics, relatively simple departures from equilibrium offer the chance to quantitatively model the resulting relaxations. These dynamics in turn provide insight on both practical and fundamental aspects of thin-film and near-surface hydrodynamics. In this talk, we will describe two model experiments —dewetting and capillary levelling— allowing to elucidate two specific problems. The first experiment was inspired by an industrial polymer processing technique called multilayer coextrusion, in which thousands of alternating polymer layers are stacked atop one another. When pushed to the limit of nanoscopic layers, the individual films are found to break up on time scales shorter than the processing time scale. A model experiment was thus developed in which we directly observe the breakup of a simple trilayer film and we here discuss the breakup dynamics.
In a second experiment, we consider hydrodynamic slip of a liquid at a solid surface, a fundamental phenomenon in fluid dynamics that governs liquid transport at small scales. For polymeric liquids, de Gennes predicted that the Navier boundary condition together with the theory of polymer dynamics imply extraordinarily large interfacial slip for entangled polymer melts on ideal surfaces. By comparing two different relatively simple departures from equilibrium, we show that the slip length manifested in a capillary-driven flow experiment in fact depends sensitively on the experimental configuration. A levelling experiment and a dewetting experiment may indeed present vastly different slip boundary conditions even when the probed materials are identical.