Dissolution dynamics of liquid/liquid binary mixtures in porous media

In this project has been undertaken an experimental study aimed at understanding the dissolution dynamics of binary mixtures within porous media. The porous medium can be roughly represented as a network of capillary tubes. This allowed for the initial research to be focused on understanding the dissolution dynamics of binary mixtures (i.e. glycerol/water, soybean oil/hexane, and isobutyric acid/water) within single capillary tubes. Further, the dissolution process was investigated within a 2D micromodel built as a network of capillary tubes. In the experiments with the capillary tubes, the dissolution (i.e. the interfacial mass transfer) could be isolated from the hydrodynamic motion while using glycerol/water and soybean oil/hexane binary mixtures. Despite the fact that these are fully miscible liquids, the interface could be observed for rather long time periods. In particular, two phase boundaries were observed moving from the ends into the middle section of the capillary tube with the speeds v?D^1/3t^-2/3d^2(D, t and d are the coefficient of diffusion, time and diameter of the capillary tube, respectively). The boundaries slowly smeared but their smearing occurred very slow in comparison to their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and could possibly be explained by the effect of barodiffusion. In addition, these solute/solvent boundaries were endowed with non-zero interfacial tension. This experimental study also revealed that the solvent penetration into the micromodel is diffusion-dominated for completely miscible binary mixtures. This is however non-Fickian diffusion with the dissolution rate dV/dt?D^1/3t^-0.4 for almost the entire duration of the experiment (V is the volume occupied by the solvent, D is the diffusion coefficient and t is time). For the IBA/water mixture the experiments performed at undercritical temperatures revealed that the diffusive mass transport was negligible despite the mixture being out of its thermodynamic equilibrium. Despite a seeming simplicity of the experiments, to the author’s best knowledge, there is no theory that could correctly describe the observed diffusional penetration of a solvent into a solute-filled capillary tube and hence, into a more complex porous volume

Dissolution dynamics of liquid/liquid binary mixtures within a micromodel

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within a glass micromodel built as a 2D regular network of capillary tubes with diameter of 0.2 mm. The micromodel is initially filled with solute and then is horizontally immersed into a thermostatic solvent-filled bath. The micromodel is open at its corners for solute dissolution to occur with no pressure gradients being applied. Our study shows that the solvent penetration into the micromodel is diffusion-dominated in completely miscible binary mixtures (glycerol/water and soybean oil/hexane). This is, however, non-Fickian diffusion with the dissolution rate, dV/dt, being proportional to D 1/3t -0.4 for almost the entire duration of the experiment (V is the volume occupied by the solvent, D is the diffusion coefficient, and t is time). For the partially miscible IBA/water mixture the experiments performed at undercritical temperatures revealed that the diffusive transport was negligible despite the mixture being out of its thermodynamic equilibrium. The water phase penetrated into some of the channels, but IBA was never completely displaced/dissolved from the micromodel and numerous interfaces remained visible after very long-time periods

Dissolution behaviour of a binary mixture in a capillary tube

We develop a pore-level physical model for the process of miscible displacement through porous media. Using the network model, the current task is reduced to the study of the dissolution dynamics of a binary mixture within a single capillary tube. Tubes of rather small diameters are considered when the typical diffusion and convective time scales are comparable. The test tube filled with the solute is immersed into the solvent-filled thermostatic bath; no pressure difference between the ends of the tubes is applied. Using a high-resolution video-camera, we study the solvent penetration into the test tube. We examine the evolution of the isobutyric acid/water mixture far from and close to the critical (consolute) point (which is 26C for this mixture). The mixture fills the circular glass tubes of diameters 0.4mm-0.8mm and of various lengths. The shape of the interface and its position are tracked and analysed. Based on our observations the following conclusions can be drawn. In all experiments, we observe a front-type propagation of the solvent phase into the tube with a clearly visible interface. The gravity force significantly affects the shape of the interface and the dissolution dynamics in all undertaken experiments. If the mixture temperature is below the critical point, then the uneven one-sided penetration of the solvent into the tube was consistently observed. The solute/solvent interface experiences oscillations of its shape (being either concave or convex at different time moments). If the mixture temperature is above the critical point, then the solvent penetrates evenly from both ends. In both under- and supercritical conditions, the contact line moves with the same speed as the interface, but the apparent contact angle is time- and coordinate-dependent. The rate of the interface propagation varies at different stages of the dissolution process and does not follow the predictions of the diffusion theory

Shapes and dynamics of miscible liquid/liquid interfaces in horizontal capillary tubes

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within horizontal capillary tubes. Tubes with diameters as small as were initially filled with one component of the binary mixture (solute) and then immersed into a solvent-filled thermostatic bath. Both ends of the tubes were open, and no pressure difference was applied between the ends. In the case of glycerol/water and soybean oil/hexane mixtures, we managed to isolate the dissolution (the interfacial mass transfer) from the hydrodynamic motion. Two phase boundaries moving from the ends into the middle section of the tube with the speeds ( and d are the coefficient of diffusion, time and the diameter of the tube, respectively) were observed. The boundaries slowly smeared but their smearing occurred considerably slower than their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and should be explained by the effect of barodiffusion. The shapes of the solute/solvent boundaries are defined by the balance between gravity and surface tension effects. The contact line moved together with the bulk interface: no visible solute remained on the walls after the interface passage. Changes in temperature and in the ratio between gravity and capillary forces altered the apparent contact angles. The IBA/water system had different behaviour. Below thecritical (consolute) point, no dissolution was observed: IBA and water behaved like two immiscible liquids, with the IBA phase being displaced from the tube by capillary pressure (the spontaneous imbibition process). Above the critical point, two IBA/water interfaces could be identified, however the interfaces did not penetrate much into the tube<br/