Small- and Large-scale Characterization and Mixing Properties in a Thermally Driven Thin Liquid Film

Abstract

Thin liquid films are nanoscopic elements of foams, emulsions and suspensions, and form a paradigm for nanochannel transport that eventually test the limits of hydrodynamic descriptions. Here we use classical dynamical systems characteristics to study the complex interplay of thermal convection, interface and gravitational forces which yields turbulent mixing and transport: Lyapunov exponents and entropies. We induce a stable two eddy convection in an extremely thin liquid film by applying a temperature gradient. Experimentally, we determine the small-scale dynamics using the motion and deformation of spots of equal size/equal color, we dubbed that technique "color imaging velocimetry". The large-scale dynamics is captured by encoding the left/right motion of the liquid directed to the left or right of the separatrix between the two rolls. This way, we characterize chaos of course mixing in this peculiar fluid geometry of a thin, free-standing liquid film.