Department of Chemical Engineering, Stanford University, Stanford, CA 94305.
Shell Global Solutions (US), Inc., Houston, TX 77082.
Proc Natl Acad Sci U S A. 2018 Jul 31;115(31):7919-7924. doi: 10.1073/pnas.1805645115. Epub 2018 Jul 16.
Foaming in liquids is ubiquitous in nature. Whereas the mechanism of foaming in aqueous systems has been thoroughly studied, nonaqueous systems have not enjoyed the same level of examination. Here we study the mechanism of foaming in a widely used class of nonaqueous liquids: lubricant base oils. Using a newly developed experimental technique, we show that the stability of lubricant foams can be evaluated at the level of single bubbles. The results obtained with this single-bubble technique indicate that solutocapillary flows are central to lubricant foam stabilization. These solutocapillary flows are shown to originate from the differential evaporation of multicomponent lubricants-an unexpected result given the low volatility of nonaqueous liquids. Further, we show that mixing of some combinations of different lubricant base oils, a common practice in the industry, exacerbates solutocapillary flows and hence leads to increased foaming.
液体中的起泡现象在自然界中无处不在。虽然已经对水基体系中的起泡机制进行了深入研究，但非水体系并未得到同样的关注。在这里，我们研究了一类广泛使用的非水液体中的起泡机制：润滑剂基础油。我们使用新开发的实验技术表明，可以在单个气泡的水平上评估润滑剂泡沫的稳定性。通过这种单泡技术获得的结果表明，溶致毛细流对于润滑剂泡沫的稳定化起着核心作用。这些溶致毛细流起源于多组分润滑剂的差异蒸发——考虑到非水液体的挥发性低，这是一个意外的结果。此外，我们还表明，在工业中常见的一些不同润滑剂基础油的混合会加剧溶致毛细流，从而导致泡沫增加。
