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

Thu 811:10-14:00P7.115Dissolution behaviour of binary mixtures in capillarytubes. Experimental studyMihaela Stevar 1 and Anatoliy Vorobev 11 University of Southampton, University Road, SO17 1BJ, Southampton, United KingdomUsing a CCD camera we examined the dissolution behaviour of two binary mixtures (glycerol/waterand isobutyric acid (IBA)/water) within capillary tubes of circular and square crosssections.Tubes with different diameters (0. 2 mm - 0. 8 mm) and lengths were used in theexperiments. A solute-filled tube was immersed into a thermostatic solvent-filled bath with nopressure gradient applied between the ends of the tube. The shape and the position of the interfacewere tracked and analysed. For the glycerol/water mixture the dissolution behaviour for differenttemperatures (20 ◦ C - 50 ◦ C) was studied. We observed two clear interfaces with finger-like shapesaffected by gravity penetrating from both ends of the tube. During the displacement process, theinterfaces retained their shape with no oscillations being observed. Towards their fusion pointminor modifications in the interfaces shapes were noticed. At higher temperatures the interfacesbecame diffuse and propagated faster. The dissolution behaviour of IBA/water mixture studied fortemperatures below and above its consolute point (26 ◦ C) was completely different. The dissolutionscenario below the critical point was characterized by the one-side penetration of the solvent intothe tube. The shape of the interface was almost flat with a small inclination in the larger diametertubes due to gravity effects. Under certain conditions the interface shape experienced quitecomplex modifications at the time of entrance, but afterwards it stabilized. The influence of thecapillary forces resulted in oscillations of the interface during its propagation. Above the criticalpoint the solvent penetrated from both sides and under-rode the solute. At higher temperature theinterfaces became diffuse and unnoticeable very quickly. The dissolution behaviours were similarin the tubes with different cross-sections. For both mixtures studied, the rate of the interfacepropagation did not follow the predictions of the diffusion theory.115