Nano Lett. 2020 Jul 8;20(7):4837-4841. doi: 10.1021/acs.nanolett.0c00709. Epub 2020 Jun 9.
Pickering emulsions are increasingly applied in the production of medicines, cosmetics, and in food technology. To apply Pickering emulsions in a rational manner it is insufficient to examine properties solely on a macroscopic scale, as this does not elucidate heterogeneities in contact angles (θ) of individual particles, which may have a profound impact on stability and microstructure. Here, we apply the super-resolution technique iPAINT to elucidate for the first time the microscopic origins of macroscopically observed emulsion phase inversions induced by a variation in particle size and aqueous phase pH. We find θ of single carboxyl polystyrene submicron particles (CPS) significantly decreases due to increasing aqueous phase pH and particle size, respectively. Our findings confirm that θ of submicron particles are both size- and pH-dependent. Interestingly, for CPS stabilized water-octanol emulsions, this enables tuning of emulsion type from water-in-oil to oil-in-water by adjustments in either particle size or pH.
Pickering 乳液在药品、化妆品和食品技术的生产中得到了越来越多的应用。为了合理地应用 Pickering 乳液，仅在宏观尺度上检查其性质是不够的，因为这不能阐明各个颗粒的接触角（θ）的不均匀性，而这可能对稳定性和微观结构有深远的影响。在这里，我们首次应用超分辨率技术 iPAINT 来阐明宏观观察到的乳液相反转的微观起源，这是由颗粒尺寸和水相 pH 的变化引起的。我们发现，由于水相 pH 值和颗粒尺寸的增加，单羧基聚苯乙烯亚微米颗粒（CPS）的θ显著降低。我们的研究结果证实了亚微米颗粒的θ既依赖于尺寸又依赖于 pH 值。有趣的是，对于 CPS 稳定的水-辛醇乳液，通过调整颗粒尺寸或 pH 值，可以将乳液类型从水包油调为油包水。
