Department of Chemical Engineering, Loughborough University, Loughborough LE 11 3TU, UK.
Department of QuímicaFísica I, Universidad Complutense, 28040 Madrid, Spain.
Adv Colloid Interface Sci. 2014 Apr;206:382-98. doi: 10.1016/j.cis.2013.08.006. Epub 2013 Sep 4.
The recent progress in theoretical and experimental studies of simultaneous spreading and evaporation of liquid droplets on solid substrates is discussed for pure liquids including nanodroplets, nanosuspensions of inorganic particles (nanofluids) and surfactant solutions. Evaporation of both complete wetting and partial wetting liquids into a nonsaturated vapour atmosphere are considered. However, the main attention is paid to the case of partial wetting when the hysteresis of static contact angle takes place. In the case of complete wetting the spreading/evaporation process proceeds in two stages. A theory was suggested for this case and a good agreement with available experimental data was achieved. In the case of partial wetting the spreading/evaporation of a sessile droplet of pure liquid goes through four subsequent stages: (i) the initial stage, spreading, is relatively short (1-2 min) and therefore evaporation can be neglected during this stage; during the initial stage the contact angle reaches the value of advancing contact angle and the radius of the droplet base reaches its maximum value, (ii) the first stage of evaporation is characterised by the constant value of the radius of the droplet base; the value of the contact angle during the first stage decreases from static advancing to static receding contact angle; (iii) during the second stage of evaporation the contact angle remains constant and equal to its receding value, while the radius of the droplet base decreases; and (iv) at the third stage of evaporation both the contact angle and the radius of the droplet base decrease until the drop completely disappears. It has been shown theoretically and confirmed experimentally that during the first and second stages of evaporation the volume of droplet to power 2/3 decreases linearly with time. The universal dependence of the contact angle during the first stage and of the radius of the droplet base during the second stage on the reduced time has been derived theoretically and confirmed experimentally. The theory developed for pure liquids is applicable also to nanofluids, where a good agreement with the available experimental data has been found. However, in the case of evaporation of surfactant solutions the process deviates from the theoretical predictions for pure liquids at concentration below critical wetting concentration and is in agreement with the theoretical predictions at concentrations above it.
讨论了包括纳米液滴、无机颗粒纳米悬浮液（纳米流体）和表面活性剂溶液在内的纯液体在固体基底上同时铺展和蒸发的理论和实验研究的最新进展。考虑了完全润湿和部分润湿液体在非饱和蒸汽气氛中的蒸发。然而，主要关注的是发生静态接触角滞后时的部分润湿情况。在完全润湿的情况下，铺展/蒸发过程分为两个阶段。针对这种情况提出了一个理论，并与现有的实验数据吻合良好。在部分润湿的情况下，纯液体的静止液滴的铺展/蒸发经历四个连续阶段：（i）初始阶段，铺展相对较短（1-2 分钟），因此在这个阶段可以忽略蒸发；在初始阶段，接触角达到前进接触角的值，液滴基底的半径达到最大值；（ii）蒸发的第一阶段的特征是液滴基底半径的恒定值；第一阶段的接触角从静态前进接触角减小到静态后退接触角；（iii）在蒸发的第二阶段，接触角保持不变，等于后退接触角，而液滴基底的半径减小；（iv）在蒸发的第三阶段，接触角和液滴基底的半径都减小，直到液滴完全消失。从理论上和实验上都证明了，在蒸发的第一和第二阶段，液滴的体积随时间的幂次 2/3 线性减小。从理论上推导出了第一阶段的接触角和第二阶段的液滴基底半径与无量纲时间的普遍关系，并通过实验得到了证实。为纯液体开发的理论也适用于纳米流体，在那里发现与现有的实验数据吻合良好。然而，在表面活性剂溶液蒸发的情况下，该过程偏离了纯液体的理论预测，在低于临界润湿浓度时，与高于该浓度的理论预测一致。
