Keane Robert K, Hong Wei, He Wei, Teale Sam, Bancroft Robbie, Dinsmore Anthony D
Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003, United States.
Langmuir. 2022 Mar 8;38(9):2821-2831. doi: 10.1021/acs.langmuir.1c02919. Epub 2022 Feb 21.
Adsorption of particles at oil-water interfaces is the basis of Pickering emulsions, which are common in nature and industry. For hydrophilic anionic particles, electrostatic repulsion and the absence of wetting inhibit spontaneous adsorption and limit the scope of materials that can be used in emulsion-based applications. Here, we explore how adding ions that selectively partition in the two fluid phases changes the interfacial electric potential and drives particle adsorption. We add oil-soluble tetrabutyl ammonium perchlorate (TBAP) to the nonpolar phase and Ludox silica nanoparticles or silica microparticles to the aqueous phase. We find a well-defined threshold TBAP concentration, above which emulsions are stable for months. This threshold increases with the particle concentration and with the oil's dielectric constant. Adding NaClO salt to water increases the threshold and causes spontaneous particle desorption and droplet coalescence even without agitation. The results are explained by a model based on the Poisson-Boltzmann theory, which predicts that the perchlorate anions (ClO) migrate into the water phase and leave behind a net positive charge in the oil. Our results show how a large class of inorganic hydrophilic, anionic nanoparticles can be used to stabilize emulsions in a reversible and stimulus-responsive way, without surface modifications.
颗粒在油水界面的吸附是皮克林乳液的基础，这种乳液在自然界和工业中都很常见。对于亲水性阴离子颗粒，静电排斥和缺乏润湿性会抑制自发吸附，并限制可用于乳液基应用的材料范围。在此，我们探究了在两种流体相中选择性分配的离子如何改变界面电势并驱动颗粒吸附。我们将油溶性高氯酸四丁铵（TBAP）添加到非极性相中，并将硅石纳米颗粒或硅石微粒添加到水相中。我们发现了一个明确的TBAP浓度阈值，高于该阈值乳液可稳定数月。该阈值随颗粒浓度和油的介电常数增加而升高。向水中添加NaClO盐会提高该阈值，甚至在不搅拌的情况下也会导致颗粒自发解吸和液滴聚并。基于泊松 - 玻尔兹曼理论的模型解释了这些结果，该模型预测高氯酸根阴离子（ClO）迁移到水相中，并在油中留下净正电荷。我们的结果表明，一大类无机亲水性阴离子纳米颗粒如何能够以可逆和刺激响应的方式用于稳定乳液，而无需进行表面改性。
