Energy Technology Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK.
J Colloid Interface Sci. 2012 Oct 1;383(1):184-97. doi: 10.1016/j.jcis.2012.06.053. Epub 2012 Jun 28.
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 0.2mm 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 v∼D(1/3)t(-2/3)d(2) (D,t 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 the critical (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.
我们报告了甘油/水、大豆油/正己烷和异丁酸（IBA）/水二元混合物在水平毛细管中溶解行为的光学观察。最初，直径小至 0.2mm 的管内充满了二元混合物的一种成分（溶质），然后浸入充满溶剂的恒温浴中。管的两端是开放的，管的两端之间没有施加压差。在甘油/水和大豆油/正己烷混合物的情况下，我们设法将溶解（界面传质）与流体力学运动隔离开来。观察到两个相界面从管的两端向中间段以速度 v∼D(1/3)t(-2/3)d(2)（D、t 和 d 分别是扩散系数、时间和管的直径）移动。边界缓慢扩散，但扩散速度明显比运动速度慢。相界面的运动不能用扩散系数对浓度的依赖性来解释，而应该用barodiffusion 的影响来解释。溶质/溶剂边界的形状由重力和表面张力效应之间的平衡决定。接触线与主体界面一起移动：界面通过后，壁上没有可见的溶质残留。温度和重力与毛细力之比的变化改变了表观接触角。IBA/水系统的行为不同。在临界点以下，没有观察到溶解：IBA 和水表现为两种不混溶的液体，IBA 相被毛细压力（自发吸吮过程）从管中排挤出来。在临界点以上，可以识别出两个 IBA/水界面，但界面没有深入到管内太多。
