Department of Chemical and Materials Engineering, National Central University , Jhongli, Taiwan 320, R.O.C.
Department of Chemical Engineering, National Taiwan University , Taipei, Taiwan 106, R.O.C.
Langmuir. 2017 Aug 1;33(30):7569-7574. doi: 10.1021/acs.langmuir.7b01384. Epub 2017 Jul 21.
Solute separation of aqueous mixtures is mainly dominated by water vaporization. The evaporation rate of an aqueous drop grows with increasing the liquid-gas interfacial area. The spontaneous spreading behavior of a water droplet on a total wetting surface provides huge liquid-gas interfacial area per unit volume; however, it is halted by the self-pinning phenomenon upon addition of nonvolatile solutes. In this work, it is shown that the solute-induced self-pinning can be overcome by gravity, leading to anisotropic spreading much faster than isotropic spreading. The evaporation rate of anisotropic spreading on a zwitterionic sulfobetaine surface is 25 times larger as that on a poly(methyl methacrylate) surface. Dramatic enhancement of evaporation is demonstrated by simultaneous formation of fog atop liquid film. During anisotropic spreading, the solutes are quickly precipitated out within 30 s, showing the rapid solute-water separation. After repeated spreading process for the dye-containing solution, the mean concentration of the collection is doubled, revealing the concentration efficiency as high as 100%. Gravity-enhanced spreading on total wetting surfaces at room temperature is easy to scale-up with less energy consumption, and thus it has great potentials for the applications of solute separation and concentration.
水溶液混合物的溶质分离主要由水蒸气化主导。水蒸发速率随液-气界面面积的增加而增大。水在完全润湿表面的自发铺展行为提供了单位体积内巨大的液-气界面面积；然而，当添加不挥发溶质时，自钉扎现象会阻止其铺展。在这项工作中，我们表明，重力可以克服溶质诱导的自钉扎，从而导致各向异性铺展比各向同性铺展快得多。在两性离子磺基甜菜碱表面上的各向异性铺展的蒸发速率比在聚甲基丙烯酸甲酯表面上的蒸发速率大 25 倍。通过在液体薄膜上同时形成雾，证明了蒸发的显著增强。在各向异性铺展过程中，溶质在 30 秒内迅速沉淀出来，表明快速的溶质-水分离。对含染料溶液进行多次铺展后，收集物的平均浓度增加了一倍，显示出高达 100%的浓缩效率。在室温下，在完全润湿表面上增强的重力铺展易于放大，且能耗低，因此在溶质分离和浓缩方面具有巨大的应用潜力。
