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

摘要CTS-9520972凯瑟琳·J·斯蒂伯约翰霍普金斯大学研究表面活性剂的吸附动力学与其结构和电荷的关系。将使用两种方法：悬挂气泡技术和振荡气泡技术，这两种技术在表面活性剂传质和热力学方面都有精确的理论描述。在表面活性剂溶液中，随着表面活性剂的扩散和吸收，悬挂式气泡的形状变得越来越长，从而减少了表面轮廓。将这些曲线与理论扩散控制弛豫曲线进行匹配，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。在振动气泡法中，形成一个小的球形气泡，使其平衡，然后在压电式活塞的作用下强迫振动。分析了径向压力振荡和气相压力振荡的相位角和幅值比，确定了扩散系数，得到了吸附-解吸系数。对于非离子表面活性剂，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，我们将研究一系列非离子表面活性剂聚氧乙烯酸酯对表面活性剂的吸附平衡和动力学。离子表面活性剂的吸附用来描述表面活性剂吸附的平衡和动力学。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。扩散通量本身就决定了下层的浓度。表面活性剂根据部分由表面电势引起的吸附动力学势垒在界面和本体之间分配。表面浓度处的电位梯度。由于假定了瞬时电性平衡，因此双电层内的电势服从古伊-查普曼分布。采用适当计入表面电势的表面状态方程和吸附等温线。这种方法将被用来建立离子表面活性剂在悬挂式气泡和振荡气泡方法中的吸附模型。对一系列长链酸进行了理论与实验的比较。

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.