School of Chemical Engineering, University of Birmingham, Birmingham, B15 2TT, UK and College of Sciences, Massey University, Auckland, 0745, New Zealand.
Department of Chemical Engineering, Imperial College London, London, SW7 2AZ, UK and School of Engineering, Cardiff University, Cardiff, CF24 3AA, UK.
Soft Matter. 2017 Jul 14;13(26):4616-4628. doi: 10.1039/c7sm00328e. Epub 2017 Jun 14.
This work focuses on the study of bulk flows accompanying the coalescence of two aqueous drops, one containing surfactant and the other surfactant-free, in silicone oils of various viscosities. It is observed that the surfactant-free drop intrudes into the surfactant-laden drop in the form of a penetrating jet whose speed increases and average radius decreases with increasing outer phase viscosity. Mixing patterns within the coalescing drops are due to the force imbalance caused by capillary pressure difference and surfactant-induced Marangoni stresses. The driving force for mixing associated with the difference in interfacial tension between the drops is considerably stronger than that related to the drop size. The long timescale mixing of the drops is driven by rapid interior convection, and the subsequent, slow, diffusive process. Three-dimensional numerical simulations show excellent qualitative and quantitative agreement with the experimental results. The implications of our results to formulation strategies of complex microstructures in practical applications are also discussed.
这项工作专注于研究两种水溶液滴（一种含有表面活性剂，另一种不含表面活性剂）在不同粘度硅油中聚结时伴随的体流动。研究发现，不含表面活性剂的液滴以穿透射流的形式侵入含有表面活性剂的液滴，射流速度随着外相粘度的增加而增加，平均半径则减小。聚结液滴内的混合模式是由毛细压差和表面活性剂诱导的马兰戈尼应力引起的力不平衡造成的。与液滴大小相关的混合驱动力与界面张力差引起的驱动力相比要大得多。与界面张力差相关的混合驱动力与液滴大小相关的混合驱动力相比要大得多。液滴的长时间混合是由快速的内部对流和随后的缓慢扩散过程驱动的。三维数值模拟与实验结果具有极好的定性和定量一致性。我们的研究结果对实际应用中复杂微观结构配方策略的意义也进行了讨论。
