8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.37Confined drying of polymer solutionsLaure Daubersies, 1 Jacques Leng, 1 and Jean-Baptiste Salmon 11 LOF, Unité Mixte Rhodia - CNRS - Bordeaux 1, 178 avenue du Dr Schweitzer, 33608,Pessac, FranceWe developed an original tool for fast screening of phase diagrams of polymers and surfactantsolutions. Our technique is based on the controlled drying of a droplet solution in a confined geometry.A L-sized droplet of an aqueous solution is confined between two wafers separated by50 m. The surfaces of the wafers are hydrophobic thanks to an appropriate coating, to avoid thepinning of the contact line. The confinement casts a well-defined timescale to the drying kinetics.We studied the drying of an aqueous solution of a copolymer thanks to microscopy combinedwith crossed-polarizer, fluorescent microscopy and Raman imaging. The first technique allowsus to follow the drying kinetics of our model system, and to identify the formation of organizedmesophases. Fluorescent microscopy allows us to track tracers inside the droplet, and to identifyunambiguously hydrodynamic recirculations probably due a Marangoni solutal effect. Finally,space and time resolved Raman spectroscopic measurements performed during drying, give accessto accurate local concentrations of the polymer solution. This technique permits to draw quantitatively,using a single confined drop, the phase diagram of the copolymer solution, with a goodaccuracy (2%). This is especially interesting, for concentrated regimes where the solution is veryviscous and hard to handle. We also developed microfluidic techniques for harvesting statistics bygenerating trains of nL-sized aqueous drops in an inert oil, and to store them in long serpentine incontact with a PDMS membrane: water inside the droplet permeates across the membrane, thusconcentrating the droplet up to the formation of dense mesophases. The large number of droplets(100) permits to get a statistical approach on the nucleation of the mesophases.37