Measuring the Kinetics of Surfactant Adsorptive - Desorptive Exchange: The Role of Surfactant Structure and Charge

摘要：本研究的目的是探讨表面活性剂的吸附动力学对其结构和电荷的依赖性。将使用两种方法；从表面活性剂传质和热力学的角度对悬垂气泡和振荡气泡技术进行了精确的理论描述。在表面活性剂溶液中，随着表面活性剂的扩散和吸收，垂坠气泡的形状变得越来越长，从而减小了表面轮廓。将这些曲线与理论扩散控制弛豫曲线相匹配，得到扩散系数。平衡数据建立了表面状态方程和吸附等温线。在振荡气泡法中，形成一个小的球形气泡，使其平衡，然后在压电活塞的作用下被迫振荡。分析了径向压力和气相压力振荡的相角和振幅比，确定了扩散系数，并得到了吸附-解吸系数。对于非离子型表面活性剂，已经建立了使用这些技术的理论框架。在本研究的第一部分，将研究一系列非离子表面活性剂聚氧乙烯酯的表面活性剂吸收平衡和动力学。离子表面活性剂的吸收用于描述表面活性剂吸收的平衡和动力学。由于德拜长度通常很小，约为1000A，因此将采用基于细德拜长度的方法。扩散通量单独决定亚层浓度。表面活性剂根据吸收动力学屏障在界面和体之间划分，吸收动力学屏障部分是由表面电位引起的。表面浓度处的电位梯度。假定瞬时电平衡，因此电势在双层内服从Gouy-Chapman分布。将采用适当考虑表面电位的表面状态方程和吸附等温线。该方法将用于建立离子表面活性剂在悬垂泡法和振荡泡法中的吸附模型。对一系列长链酸，将理论与实验进行比较。

ABSTRACT CTS-9520972 Kathleen J. Stebe Johns Hopkins University The aim of this study is to probe the dependence of the absorption kinetics of surfactants on their structure and charge. Two methods will be used; the pendant bubble and the oscillating bubble techniques, which have precise theoretical descriptions in terms of surfactant mass transfer and thermodynamics. The shape of a pendant bubble in surfactant solution becomes increasingly elongated as surfactant diffuses and absorbs, reducing the surface profiles. These profiles are matched to theoretical diffusion controlled relaxation's to obtain diffusion coefficients. Equilibrium data establish the surface equation of state and the adsorption isotherm. In the oscillating bubble method a small spherical bubble is formed, equilibrated, and subsequently forced to oscillate by the action of a piezo-piston. Phase angles and amplitude ratios between the radial and gas phase pressure oscillations are analyzed to confirm the diffusivities and to obtain the adsorption-desorption coefficients. For non-ionic surfactants, the theoretical framework to use these techniques has been established. In the first part of this study, the equilibrium and dynamics of surfactant absorption of a homologous series of nonionic surfactants, the polyethoxylates, will be studied. The absorption of ionic surfactants used to describe the equilibrium and dynamics of surfactant absorption. Because Debye lengths are typically small, of order 1000A, an approach based on a thin Debye length will be adopted. Diffusive flux alone determines the sublayer concentration. Surfactant partitions between the interface and the bulk according to an absorption kinetic barrier which is caused, in part, by the surface potential. The potential gradient at the surface concentration. Instantaneous electrical equilibrium is assumed, so the potential obeys a Gouy-Chapman distribution within the double layer. A surface equation of state and adsorption isotherm tha t properly incorporate the surface potential will be adopted. This approach will be used to develop models for ionic surfactant adsorption in the pendant bubble and in the oscillating bubble methods. Theory will be compare to experiment for the a series of the long chain acids.