Department of Materials Science & Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Department of Mathematics, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Phys Rev E. 2017 Nov;96(5-1):053102. doi: 10.1103/PhysRevE.96.053102. Epub 2017 Nov 6.
We present an experimental study of pattern formation during the penetration of an aqueous surfactant solution into a liquid fatty acid in a Hele-Shaw cell. When a solution of the cationic surfactant cetylpyridinium chloride is injected into oleic acid, a wide variety of fingering patterns are observed as a function of surfactant concentration and flow rate, which are strikingly different than the classic Saffman-Taylor (ST) instability. We observe evidence of interfacial material forming between the two liquids, causing these instabilities. Moreover, the number of fingers decreases with increasing flow rate Q, while the average finger width increases with Q, both trends opposite to the ST case. Bulk rheology on related mixtures indicates a gel-like state. Comparison of experiments using other oils indicates the importance of pH and the carboxylic head group in the formation of the surfactant-fatty acid material.
我们在 Hele-Shaw 细胞中展示了一种水基表面活性剂溶液在液体脂肪酸中渗透时的图案形成的实验研究。当将阳离子表面活性剂十六烷基吡啶氯化物溶液注入油酸中时，观察到各种类型的指状图案，这些图案的形成与表面活性剂浓度和流速有关，与经典的 Saffman-Taylor（ST）不稳定性有很大的不同。我们观察到两种液体之间形成界面物质的证据，这导致了这些不稳定性。此外，随着流速 Q 的增加，指状的数量减少，而平均指状宽度随 Q 的增加而增加，这两种趋势与 ST 情况相反。对相关混合物的体流变学研究表明，它们处于凝胶状状态。使用其他油进行的实验比较表明，pH 值和羧酸头基在表面活性剂-脂肪酸材料的形成中非常重要。
