Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK.
Instituto de Carboquímica ICB-CSIC, Miguel Luesma Castán 4, 50018 Zaragoza, Spain.
J Colloid Interface Sci. 2022 Feb 15;608(Pt 2):2025-2038. doi: 10.1016/j.jcis.2021.10.130. Epub 2021 Oct 27.
Surfactants in emulsions sometimes do not provide adequate stability against coalescence, whereas Pickering emulsions often offer greater stability. In a search for stabilizers offering biocompatibility, we hypothesized that carboxylated nanodiamonds (ND) would impart stability to Pickering emulsions.
We successfully prepared Pickering emulsions of sunflower oil in water via two different methods: membrane emulsification and probe sonication. The first method was only possible when the pH of the aqueous ND suspension was ≤ 4.
Pendant-drop tensiometry confirmed that carboxylated ND is adsorbed at the oil/water interface, with a greater decrease in interfacial tension found with increasing ND concentrations in the aqueous phase. The carboxylated ND become more hydrophilic with increasing pH, according to three-phase contact angle analysis, because of deprotonation of the carboxylic acid groups. Membrane emulsification yielded larger (about 30 µm) oil droplets, probe sonication produced smaller (sub-μm) oil droplets. The Pickering emulsions show high stability against mechanical vibration and long-term storage for one year. They remain stable against coalescence across a wide range of pH values. Sonicated emulsions show stability against creaming. In this first-ever systematic study of carboxylated ND-stabilized Pickering emulsions, we demonstrate a promising application in the delivery of β-carotene, as a model active ingredient.
乳液中的表面活性剂有时不能提供足够的稳定性来防止聚结，而 Pickering 乳液通常提供更大的稳定性。在寻找具有生物相容性的稳定剂时，我们假设羧基化纳米金刚石 (ND) 将赋予 Pickering 乳液稳定性。
我们通过两种不同的方法成功制备了葵花籽油在水中的 Pickering 乳液：膜乳化和探针超声。第一种方法只有在水相 ND 悬浮液的 pH 值≤4 时才有可能。
悬滴张力计证实羧基化 ND 在油/水界面上被吸附，随着水相中 ND 浓度的增加，界面张力下降得更大。根据三相接触角分析，随着 pH 值的增加，羧基化 ND 变得更亲水，因为羧酸基团的去质子化。膜乳化产生较大的（约 30 µm）油滴，探针超声产生较小的（亚微米）油滴。Pickering 乳液在机械振动和长达一年的长期储存中表现出很高的稳定性。它们在很宽的 pH 值范围内保持稳定，不会发生聚结。超声乳化乳液具有抗乳状液稳定性。在这项首次对羧基化 ND 稳定的 Pickering 乳液的系统研究中，我们展示了在递送β-胡萝卜素作为模型活性成分方面的有前途的应用。
