从胶束水混合物的扩散驱动稀释确定临界胶束浓度,Langmuir

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从胶束水混合物的扩散驱动稀释确定临界胶束浓度
Langmuir ( IF 3.7 ) Pub Date : 2021-02-17 , DOI: 10.1021/acs.langmuir.1c00176
Eliandreina Cruz Barrios ₁ , Onofrio Annunziata ₁

Affiliation

胶束化是表面活性剂溶液中至关重要的现象。在这里，我们证明了胶束水溶液和纯水之间自由边界的基于扩散的扩散产生了表面活性剂浓度的一维空间分布，可用于识别临界胶束浓度，此处表示为C *。之所以能够做到这一点，是因为胶束在水中的稀释会导致它们沿浓度分布曲线在明确定义的位置解离，并突然增加扩散系数。瑞利干涉法已成功用于确定C*在25°C的水中三种著名的表面活性剂的值：Triton X-100（TX-100），十二烷基硫酸钠（SDS）和聚（氧乙烯）（4）月桂基醚（Brij-30）。在Na ₂ SO ₄，NaCl和NaSCN的存在下，对于TX-100，还表征了C *对盐浓度的依赖性。C的准确值*可以通过目视检查相应的浓度梯度曲线直接识别。为了将最小二乘法应用到实验浓度曲线，从菲克定律和胶束化的伪相分离模型（包括适当的修改）中得出了数学表达式。尽管在我们的实验中采用了瑞利干涉测量法，但该方法可以扩展到产生表面活性剂浓度的一维分布图的任何实验技术。而且，扩散驱动的表面活性剂分解是精确，无创的，需要单样品制备，并且适用于非离子和离子表面活性剂。因此，这项工作为扩散驱动的稀释方法奠定了基础，从而代表了现有技术的宝贵补充，可用于确定C *。

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Determination of Critical Micelle Concentration from the Diffusion-Driven Dilution of Micellar Aqueous Mixtures

Micellization is a phenomenon of central importance in surfactant solutions. Here, we demonstrate that the diffusion-based spreading of the free boundary between a micellar aqueous solution and pure water yields a one-dimensional spatial profile of surfactant concentration that can be used to identify the critical micelle concentration, here denoted as C*. This can be achieved because dilution of micelles into water leads to their dissociation at a well-defined position along the concentration profile and an abrupt increase in the diffusion coefficient. Rayleigh interferometry was successfully employed to determine C* values for three well-known surfactants in water at 25 °C: Triton X-100 (TX-100), sodium dodecyl sulfate (SDS), and poly(oxyethylene)(4)Lauryl Ether (Brij-30). The dependence of C* on salt concentration was also characterized for TX-100 in the presence of Na₂SO₄, NaCl, and NaSCN. Accurate values of C* can be directly identified by visual inspection of the corresponding concentration-gradient profiles. To apply the method of least squares to experimental concentration profiles, a mathematical expression was derived from Fick’s law and the pseudophase separation model of micellization with the inclusion of appropriate modifications. While Rayleigh interferometry was employed in our experiments, this approach can be extended to any experimental technique that yields one-dimensional profiles of surfactant concentration. Moreover, diffusion-driven surfactant disaggregation is precise, noninvasive, requires single-sample preparation, and applies to both nonionic and ionic surfactants. Thus, this work provides the foundation of diffusion-driven dilution methods, thereby representing a valuable addition to existing techniques for the determination of C*.

更新日期：2021-03-02

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