Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
J Colloid Interface Sci. 2011 Mar 1;355(1):231-6. doi: 10.1016/j.jcis.2010.11.077. Epub 2010 Nov 30.
Detailed surfactant transport studies have typically been restricted to the air-water interface. This is mainly due to the lack of experimental devices and techniques available to study liquid-liquid interfaces. As a result, there is a lack of relevant data and understanding of surfactant behavior in microfluidic studies and emulsion applications. Using a novel shape fitting algorithm for a pendant drop capable of handling fluids of similar densities, i.e. low Bond numbers, we measure the dynamic surface tension as a function of bulk surfactant concentration at the silicone oil-water interface for a homologous series of C(i)E(8) nonionic surfactants. We show that the isotherms governing equilibrium at the oil-water and air-water interfaces are very different. Using a scaling analysis comparing two governing mass transport timescales, we demonstrate that there exists a transition from diffusion-limited to kinetic-limited dynamics at the silicone oil-water interface. Adsorption rate constants are determined from a one parameter nonlinear fit to dynamic surface tension data. These results demonstrate that the dynamics of interfacial transport are highly dependent on the immiscible fluids that form the interface.
详细的表面活性剂传输研究通常局限于气-水界面。这主要是由于缺乏可用于研究液-液界面的实验设备和技术。因此，在微流控研究和乳液应用中，缺乏有关表面活性剂行为的相关数据和认识。我们使用一种新的悬滴拟合算法，该算法能够处理密度相似的流体，即低 Bond 数，来测量在一系列同系的 C(i)E(8)非离子表面活性剂在硅油-水界面上作为体相表面活性剂浓度函数的动态表面张力。我们表明，控制油水和水气界面平衡的等温线非常不同。通过比较两个控制质量传输时间尺度的缩放分析，我们证明在硅油-水界面上存在从扩散限制到动力学限制的转变。从对动态表面张力数据的单参数非线性拟合中确定吸附速率常数。这些结果表明，界面传输的动力学高度依赖于形成界面的不混溶流体。
