Confined drying of a complex fluid drop: phase diagram, activity, and mutual diffusion coefficient

Abstract

We describe a drying setup where a liquid drop of a molecular mixture is confined between two circular plates and left to evaporate in a controlled manner. The direct observation of the drying kinetics in such a confined geometry, which includes the measurement of the volume of the drop against time and the monitoring of a series of nucleation events, permits the reconstruction of a rough phase diagram for the case of an aqueous triblock copolymer solution. Accurate estimations of the phase boundaries are obtained thanks to spatially-resolved Raman spectroscopic measurements of the temporal evolution of the solute concentration field within the drop. The comparison of such measurements with a theoretical model describing the drying kinetics of binary mixtures [L. Daubersies and J. B. Salmon, Phys. Rev. E, 2011, 84, 031406] yields estimations of the activity of the solution and of its mutual diffusion coefficient against the solute concentration.