Dinkgreve M, Velikov K P, Bonn D
Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1018 XH Amsterdam, The Netherlands.
Unilever R&D Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands and Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Phys Chem Chem Phys. 2016 Aug 17;18(33):22973-7. doi: 10.1039/c6cp03572h.
Colloidal particles are often used to make Pickering emulsions that are reported to be very stable. Commonly the stabilization is a combined effect of particle adsorbing at the fluid interface and a particle network in the continuous phase; the contribution of each to the overall stability is difficult to assess. We investigate the role of LAPONITE® particles on high internal phase emulsion stability by considering three different situations: emulsion stabilization by surfactant only, by surfactant plus clay particles, and finally clay particles only. To clarify the structure of the emulsion and the role of the clay particles, we have succeeded in fluorescently labelling the clay particles by adsorbing the dye onto the particle surfaces. This allows us to show directly using confocal microscopy, that the clay particles are not only located at the interface but also aggregate and form a gel in the continuous aqueous phase. We show that the emulsions in the presence of surfactant (with or without clay) are stable to coalescence and shear. Without surfactant (with only LAPONITE® as stabilizer) the emulsions are stable to coalescence for several weeks, however they destabilize rapidly under shear. Our results suggest that the formation of the emulsions is mostly due to gel formation of the clay particles in the continuous phase, rather than that the clay is an emulsifier. This gel formation also accounts for the instability of the emulsions to shear that we observe caused by shear thinning of the continuous gel and inability of the adsorbed particles to rearrange effectively around the droplets due to their attractive nature.
胶体颗粒常被用于制备据报道非常稳定的皮克林乳液。通常情况下，稳定性是颗粒吸附在流体界面以及连续相中颗粒网络的综合作用；各自对整体稳定性的贡献难以评估。我们通过考虑三种不同情况来研究锂皂石颗粒对高内相乳液稳定性的作用：仅由表面活性剂稳定乳液、由表面活性剂加粘土颗粒稳定乳液，以及最后仅由粘土颗粒稳定乳液。为了阐明乳液的结构以及粘土颗粒的作用，我们成功地通过将染料吸附到颗粒表面对粘土颗粒进行了荧光标记。这使我们能够直接利用共聚焦显微镜观察到，粘土颗粒不仅位于界面处，还会聚集并在连续水相中形成凝胶。我们表明，在有表面活性剂（有或没有粘土）存在的情况下，乳液对聚结和剪切是稳定的。没有表面活性剂（仅以锂皂石作为稳定剂）时，乳液在几周内对聚结是稳定的，然而它们在剪切作用下会迅速失稳。我们的结果表明，乳液的形成主要是由于连续相中粘土颗粒形成凝胶，而不是因为粘土是一种乳化剂。这种凝胶的形成也解释了我们观察到的乳液在剪切作用下的不稳定性，这是由于连续凝胶的剪切变稀以及吸附颗粒因其吸引力性质无法在液滴周围有效重排所致。
