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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Three-stage multilayer formation kinetics during adsorption of an anionic fluorinated surfactant onto germanium. 1. Concentration effect
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Three-stage multilayer formation kinetics during adsorption of an anionic fluorinated surfactant onto germanium. 1. Concentration effect

机译：阴离子氟化表面活性剂吸附到锗上的三阶段多层形成动力学。 1.集中效应

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摘要

The adsorption of tetraethylammonium perfluorooctylsulfonate (TEA-FOS) from aqueous solution onto hydroxylated germanium is studied using in situ polarized attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The adsorption is monitored at a series of bulk solution concentrations spanning from well below to above the critical micelle concentration (CMC; 1.0 mM). The kinetics of adsorption is followed by monitoring the intensity of the fluorocarbon bands. The orientation of the fluorocarbon director with respect to the germanium surface is determined by circular dichroism measurements of CF2 stretching bands. At bulk concentrations ranging from 10% of the CMC to at least 500% of the CMC, the adsorption occurs in an unusual sequence of three stages. Initially, rapid adsorption occurs within 200 min, leading to coverage of a monolayer or less. A long period of slow adsorption follows, during which we hypothesize that surfactant molecules form clusters, some of which serve as nuclei for multilayer growth. This stage concludes suddenly with an acceleration in the rate of adsorption, which eventually leads to multilayer formation. Because this is an anionic surfactant adsorbing onto a negatively charged surface at pH 6, the tetraethyl ammonium ions must mediate the interactions between the surfactant headgroups and the surface. The dichroism measurements show that TEA-FOS is initially oriented randomly or somewhat parallel to the surface, but over time adopts an orientation somewhat normal to the surface. This behavior is consistent with initial adsorption at isolated sites, followed by aggregation into isotropic admicelles, and finally growth into flattened admicelles. The sudden onset of accelerated adsorption can be explained either by autoaccelerating adsorption or nucleation and growth of a hydrophobic multilayer structure.
机译：使用原位偏振衰减全反射傅里叶变换红外光谱（ATR-FTIR）研究了全氟辛基磺酸四乙铵（TEA-FOS）从水溶液到羟基化锗的吸附。在一系列大范围溶液浓度（从远低于临界胶束浓度（CMC; 1.0 mM））的范围内监测吸附。吸附动力学之后是监测碳氟化合物带的强度。碳氟指向矢相对于锗表面的取向是通过CF2拉伸带的圆二色性测量确定的。在从CMC的10％到CMC的至少500％的总体浓度范围内，吸附以三个阶段的异常顺序发生。最初，快速吸附会在200分钟内发生，从而导致单层或以下的覆盖。接下来是长时间的缓慢吸附，在此期间，我们假设表面活性剂分子形成簇，其中一些充当多层生长的核。该阶段突然结束，吸附速率加快，最终导致多层形成。由于这是一种阴离子表面活性剂，在pH 6时会吸附到带负电荷的表面上，因此四乙基铵离子必须介导表面活性剂头基与表面之间的相互作用。二向色性测量表明，TEA-FOS最初是随机地取向或稍微平行于表面，但是随着时间的流逝，采用的取向是稍微垂直于表面的取向。这种行为与在分离位置的初始吸附，随后聚集成各向同性的胶束，最后生长成扁平的胶束相一致。加速吸附的突然开始可以通过自动加速吸附或疏水性多层结构的成核和生长来解释。

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