Nanikashvili Pilkhaz M, Butenko Alexander V, Deutsch Moshe, Lee Daeyeon, Sloutskin Eli
Department of Physics, Bar-Ilan University, Ramat-Gan 5290002, Israel; Bar-Ilan Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
J Colloid Interface Sci. 2022 Sep;621:131-138. doi: 10.1016/j.jcis.2022.03.146. Epub 2022 Apr 4.
The counterintuitive temperature-controlled self-faceting of water-suspended, surfactant-stabilized, liquid oil droplets provides new opportunities in engineering of smart liquids, the properties of which are controllable by external stimuli. However, many emulsions exhibiting self-faceting phenomena have limited stability due to surfactant precipitation. The emulsions' stability may be enhanced, and their inter-droplet electrostatic repulsion tuned, through controlled charge screening driven by varying-concentration added salts. Moreover, in many technologically-relevant situations, salts may already exist in the emulsion's aqueous phase. Yet, salts' impact on self-faceting effects has never been explored. We hypothesize that the self-faceting transitions' temperatures, and stability against surfactant precipitation, of ionic-surfactants-stabilized emulsions are significantly modified by salt introduction.
We explore the temperature-dependent impact of NaCl and CsCl salt concentration on the emulsions' phase diagrams, employing optical microscopy of emulsion droplet shapes and interfacial tension measurements, both sensitive to interfacial phase transitions.
A salt concentration dependent increase in the self-faceting transition temperatures is found, and its mechanism elucidated. Our findings allow for a significant enhancement of the emulsions' stability, and provide the physical understanding necessary for future progress in research and applications of self-faceting phenomena in salt-containing emulsions.
水悬浮、表面活性剂稳定的液态油滴呈现出违反直觉的温度控制自刻面现象，这为智能液体工程带来了新机遇，此类智能液体的性质可由外部刺激控制。然而，许多呈现出自刻面现象的乳液由于表面活性剂沉淀而稳定性有限。通过添加不同浓度的盐驱动的可控电荷筛选，可以提高乳液的稳定性，并调节其液滴间的静电排斥力。此外，在许多技术相关的情况下，乳液的水相中可能已经存在盐。然而，盐对自刻面效应的影响从未被研究过。我们假设，引入盐会显著改变离子表面活性剂稳定的乳液的自刻面转变温度以及抗表面活性剂沉淀的稳定性。
我们利用对界面相变敏感的乳液液滴形状光学显微镜和界面张力测量，探究了NaCl和CsCl盐浓度对乳液相图的温度依赖性影响。
发现了自刻面转变温度随盐浓度的增加，并阐明了其机制。我们的发现能够显著提高乳液的稳定性，并为含盐乳液中自刻面现象的研究和应用的未来进展提供必要的物理理解。
