We investigated the interfacial instability of emulsion droplets via in situ measuring the oil/water interfacial tension (IFT) using the capillary suction method. The discrete phase of the oil-in-water emulsion contains a hydrophobic polymer (polystyrene, PS) and a fatty alcohol cosurfactant n-cetyl alcohol (CA) or n-octadecanol (OD), both of which were dissolved in an organic solvent (chloroform). The continuous phase is an aqueous solution of surfactant (sodium dodecyl sulfate, SDS). Upon removal of the organic solvent, the concentrations of CA and PS increase gradually, which induce a continual decrease of the IFT until the occurrence of interfacial instability. Micropipette tensiometry performed on an evaporating emulsion droplet reveals that interfacial instability is triggered when the IFT decreases close to ∼0.17 mN/m. As a result, micron particles with wrinkled surfaces can be obtained after the complete removal of the organic solvent. The effect of the initial concentration and alkyl chain length of the cosurfactant on the interfacial instability and surface roughness of the formed particles was studied. This study provides theoretical guidance for the preparation of micrometer-sized polymer particles with diverse morphologies via the interfacial instability of emulsion droplets.

中文翻译：

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包含聚合物和脂肪醇的乳液液滴的界面不稳定性

我们通过使用毛细管抽吸法原位测量油/水界面张力（IFT），研究了乳液液滴的界面不稳定性。水包油乳液的不连续相包含疏水性聚合物（聚苯乙烯，PS）和脂肪醇表面活性剂正十六醇（CA）或正构醇。-十八烷醇（OD），两者均溶解在有机溶剂（氯仿）中。连续相是表面活性剂（十二烷基硫酸钠，SDS）的水溶液。除去有机溶剂后，CA和PS的浓度逐渐增加，这导致IFT持续降低，直到出现界面不稳定性为止。对蒸发的乳液液滴进行的微量移液器张力测定表明，当IFT降低至接近〜0.17 mN / m时，将触发界面不稳定性。结果，在完全除去有机溶剂之后，可以获得具有皱纹表面的微米颗粒。研究了助表面活性剂的初始浓度和烷基链长对所形成颗粒的界面不稳定性和表面粗糙度的影响。