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Effect of soluble surfactants on pinch-off of moderately viscous drops and satellite size
Journal of Colloid and Interface Science ( IF 9.9 ) Pub Date : 2018-01-11 , DOI: 10.1016/j.jcis.2018.01.039
Nina M. Kovalchuk , Hannah Jenkinson , Reinhard Miller , Mark J.H. Simmons

Hypothesis

Surfactant redistribution in a liquid bridge close to drop detachment depends on competition between the bridge deformation rate and surfactant equilibration rate. Surfactant effect can be different in situations when diffusion coefficient changes independently of thinning kinetics or in line with it. Using moderately viscous liquids should allow both situations to be explored experimentally.

Experiments

Formation of liquid drops at the tip of capillary is studied experimentally for silicone oils and for surfactant-laden and surfactant-free water/glycerol mixtures of moderate viscosity with particular attention to the kinetics of liquid bridge close to pinch-off and formation of satellite droplets.

Findings

Effect of surfactant depends on the dynamic regime of the bridge thinning. In the presence of surfactant, inertial kinetics slows down close to pinch-off demonstrating effective surface tension smaller than dynamic surface tension. An acceleration of thinning kinetics caused by depletion of surfactant from the liquid bridge was observed in viscous and visco-inertial regimes. The size of satellite droplets has a maximum versus viscosity; increasing with surfactant concentration at smaller viscosities and decreasing with an increase of surfactant concentration at largest studied viscosity, where inversion of the pinch-off point was observed for surfactant solutions.



中文翻译:

可溶性表面活性剂对中等粘度液滴的夹断和卫星尺寸的影响

假设

在接近液滴分离的液桥中,表面活性剂的重新分布取决于桥变形速率和表面活性剂平衡速率之间的竞争。在扩散系数独立于稀化动力学变化或与其一致的情况下,表面活性剂的作用可能会有所不同。使用中等粘度的液体应允许通过实验探索两种情况。

实验

对于硅油以及中等粘度的载有表面活性剂和不含表面活性剂的水/甘油混合物,实验研究了毛细管尖端的液滴形成,尤其要注意接近夹断和形成卫星液滴的液桥动力学。 。

发现

表面活性剂的作用取决于桥变薄的动态范围。在存在表面活性剂的情况下,惯性动力学会变慢,接近夹断,表明有效表面张力小于动态表面张力。在粘性和惯性状态下,观察到由表面活性剂从液桥中耗尽引起的稀化动力学加速。卫星液滴的大小相对于粘度具有最大值。在较小的粘度下,随着表面活性剂浓度的增加而增加,而在最大研究粘度下,随着表面活性剂浓度的增加而降低,其中观察到表面活性剂溶液的夹断点反转。

更新日期:2018-01-11
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