Department of Chemical and Biomolecular Engineering, University of Pennsylvania , Philadelphia, Pennsylvania, 19104, United States.
Langmuir. 2013 Oct 15;29(41):12679-87. doi: 10.1021/la402897d. Epub 2013 Oct 2.
One of the most important properties of emulsions is their stability. Most emulsions stabilized with molecular surfactants tend to lose their stability over time via different mechanisms. Although the stability of emulsions stabilized with homogeneous particles have been shown to be superior to that of surfactant-stabilized emulsions, these Pickering emulsions nevertheless are only kinetically stable and thus can undergo destabilization. Janus particles that have two opposite wetting surfaces have shown promise in imparting emulsions with long-term stability because of their strong attachment to the oil-water interface. In this theoretical study, we consider thermodynamics of emulsion stabilization using amphiphilic Janus dumbbells, which are nonspherical particles made of two partially fused spherical particles of opposite wettability. These amphiphilic dumbbells are attractive candidates as colloid surfactants for emulsion stabilization because highly uniform Janus dumbbells can be synthesized in large quantities; thus, their application in emulsion stabilization can become practical. Our theoretical calculation demonstrates that Janus dumbbells can indeed generate thermodynamically stable Pickering emulsions. In addition, we also find that there exists a total oil-water interfacial area that results in the lowest energy state in the system, which occurs when Janus dumbbells available in the system are completely consumed to fully cover the droplet interfaces. We show that the geometry of dumbbells as well as the composition of the emulsion mixtures has significant influences on the average size of dumbbell-stabilized emulsions. We also investigate the effect of asymmetry of Janus dumbbells on the average droplet radius. Our results clearly show that amphiphilic Janus dumbbells provide unique opportunities in stabilizing emulsions for various applications.
乳液的一个重要性质是其稳定性。大多数用分子表面活性剂稳定的乳液往往会通过不同的机制随着时间的推移而失去稳定性。虽然用均匀颗粒稳定的乳液的稳定性被证明优于表面活性剂稳定的乳液，但这些 Pickering 乳液仍然只是动力学稳定的，因此可能会发生失稳。具有两个相反润湿性表面的 Janus 粒子由于其与油水界面的强烈附着，在赋予乳液长期稳定性方面显示出了很大的潜力。在这项理论研究中，我们考虑了使用两亲性 Janus 哑铃来稳定乳液的热力学，两亲性 Janus 哑铃是由两个具有相反润湿性的部分融合的球形粒子组成的非球形粒子。这些两亲性哑铃作为胶体表面活性剂在乳液稳定中具有吸引力，因为可以大量合成高度均匀的 Janus 哑铃；因此，它们在乳液稳定中的应用可以变得实用。我们的理论计算表明，Janus 哑铃确实可以产生热力学稳定的 Pickering 乳液。此外，我们还发现存在一个总油水界面面积，它导致系统的最低能量状态，当系统中可用的 Janus 哑铃完全消耗以完全覆盖液滴界面时，就会出现这种情况。我们表明，哑铃的几何形状以及乳液混合物的组成对哑铃稳定乳液的平均尺寸有显著影响。我们还研究了 Janus 哑铃不对称性对平均液滴半径的影响。我们的结果清楚地表明，两亲性 Janus 哑铃为各种应用的乳液稳定提供了独特的机会。
