Laser Fluorescence Studies of Interfacial Diffusional Processes (REU Supplement)

采用先进的激光荧光仪，通过光漂白后的荧光恢复，测定了单分子膜中荧光标记探针在气液界面的表面或平移扩散系数。研究了分子堆积、温度和各种离子对单、双烃链表面活性剂体系平移迁移率的影响。光漂白后荧光恢复方法避免了与测量表面扩散的放射性示踪剂技术相关的许多问题。这项实验技术还允许人们将表面扩散的研究扩展到以前无法用放射性示踪剂方法研究的界面系统。此外，人们还能够区分发生在单分子膜中的流动和扩散传输过程。该程序首次提供了可靠的表面扩散系数实验值，以检验最近发展的表面扩散理论模型，并阐明流体/流体界面的二维传质性质。本研究的结果具有广泛的适用性，包括纸浆和造纸加工。表面扩散系数的可靠数值需要用于各种毛细管波和薄膜的稳定性，这反过来又对评估和了解纸浆和造纸工业中的泡沫问题非常重要。表面流动性对泡沫的稳定性很重要；然而，这一参数的实验测定几乎是不存在的。对界面传质的研究旨在克服这一严重局限性，结合界面流变性测量，将有助于促进对泡沫的理解，并有助于开发改进的泡沫抑制剂和泡沫破碎剂。

An advanced laser fluorescence apparatus is employed to determine the surface or translational diffusion coefficients of fluorescent-labeled probes in monomolecular films at air-water interfaces using fluorescence recovery after photobleaching. The effects of molecular packing, temperature, and various ions on the translational mobility in single and double hydrocarbon-chain surfactant systems are investigated. The fluorescence-recovery-after-photobleaching approach avoids many of the problems associated with the radiotracer technique for measuring surface diffusion. This experimental technique also permits one to extend the study of surface diffusion to interfacial systems previously inaccessible to study by the radiotracer method. In addition, one is able to distinguish between flow and diffusional transport processes occurring in monomolecular films. The procedure provides, for the first time, reliable experimental values of the surface diffusion coefficient to test a recently developed theoretical model of surface diffusion and to elucidate the nature of two- dimensional mass transfer at fluid/fluid interfaces. The results of this research have applicability to a wide range of areas, including pulp and paper processing. Reliable values of the surface diffusion coefficient are needed for use in a variety capillary waves and the stability of thin films which, in turn, are very important to evaluating and understanding foam problems in the pulp and paper industry. Surface mobility is important in the stability of foam; however, experimental determinations of this parameter are virtually nonexistent. This research on interfacial mass transfer is directed to overcoming this serious limitation; when combined with interfacial rheological measurements, it will assist in advancing the understanding of foams and the development of improved foam inhibitors and foam breakers.