Department of Physics and John A. Paulson School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts02138, United States.
BioSense Institute, University of Novi Sad, Dr Zorana Djindjica 1, Novi Sad21000, Serbia.
Langmuir. 2023 Feb 14;39(6):2152-2160. doi: 10.1021/acs.langmuir.2c02346. Epub 2023 Feb 6.
A straightforward method for visualization and quantification of surfactant effectiveness within different electrolyte environments based on using reconfigurable Janus emulsions as novel optical probes is reported. More specifically, we investigated the effect of different types and concentrations of salt counter-ions on the surfactant surface excess of commercial ionic and non-ionic surfactants, namely sodium dodecyl sulfate (SDS) and Tween 80 via in situ monitoring the morphological reconfigurations of biphasic Janus emulsions comprising hydrocarbon and fluorocarbon oils. We find that significant variations in interfacial tensions of SDS-stabilized interfaces (up to 15 mN·m) can be evoked by titrating mono-, di-, and trivalent cationic counter-ions, which is coherent with the lyotropic (Hofmeister) series. In contrast, the salt counter-ion effect on the surfactant effectiveness was less pronounced for the non-ionic surfactant Tween 80 (∼3 mN·m). Our results reveal a facile in situ method for monitoring the central role of electrolyte type and concentration on surfactant effectiveness and, more broadly, illustrate that Janus emulsions serve as powerful optical probes to dynamically study the properties of surfactants at liquid interfaces. We demonstrate the utility of our findings for an electro-induced morphological reconfiguration of Janus droplet morphologies by dynamically tuning Cu concentration in solution using an electrode setup. The latter provides a unique platform for liquid-phase, real-time, and continuous tuning of Janus droplet morphologies, e.g., for their application in sensing and dynamic optical device platforms.
本文报道了一种基于可重构单分子层 Janus 乳液作为新型光学探针，可视化和定量不同电解质环境中表面活性剂效力的直接方法。更具体地说，我们通过原位监测由烃油和氟碳油组成的双相单分子层 Janus 乳液的形态重构，研究了不同类型和浓度的盐反离子对商业离子型和非离子型表面活性剂（即十二烷基硫酸钠（SDS）和吐温 80）的表面活性剂表面过剩的影响。我们发现，通过滴定单价、二价和三价阳离子反离子，可以引起 SDS 稳定界面的界面张力发生显著变化（高达 15 mN·m），这与溶致（Hofmeister）序列一致。相比之下，盐反离子对非离子表面活性剂吐温 80 的表面活性剂效力的影响较小（约 3 mN·m）。我们的结果揭示了一种简便的原位监测方法，可以研究电解质类型和浓度对表面活性剂效力的核心作用，更广泛地说明了 Janus 乳液作为动态研究表面活性剂在液-液界面上性质的有力光学探针。我们通过使用电极装置动态调节溶液中的 Cu 浓度来演示 Janus 液滴形态的电诱导形态重构的方法的实用性。后者提供了一个独特的液相、实时和连续调节 Janus 液滴形态的平台，例如，将其应用于传感和动态光学器件平台。
