Suppression of Interfacial Instabilities using Soft, Deformable Solid Coatings

Abstract

Interfacial instabilities in multilayer flows of immiscible liquid layers are often driven by viscosity contrasts in Newtonian liquids and/or elasticity contrasts in the case of polymeric liquids. Such instabilities, when present, can often be detrimental to many applications such as coating applications and polymer extrusion processes. In this review, we summarize our research which has explored the possibility of using a soft solid layer coating to manipulate interfacial instabilities. We have explored a variety of geometric configurations, as well as fluid constitutive behavior. We show that in general, it is possible to suppress interfacial instabilities in both Newtonian and polymeric liquids by lining the rigid wall with a deformable solid layer. We show that there is a window of parameters (shear modulus, layer thickness, ratio of solid to fluid viscosity) where the solid layer suppresses the interfacial instabilities at all wavenumbers without triggering new instabilities. We also show that solid layer deformability can further be used to promote interfacial instabilities in core–annular flows. This could be potentially used in microfluidic applications which are used to prepare monodisperse droplets and emulsions.