Luu Xuan-Cuong, Striolo Alberto
School of Chemical, Biological, and Materials Engineering, University of Oklahoma , Norman, Oklahoma 73019, United States.
J Phys Chem B. 2014 Nov 26;118(47):13737-43. doi: 10.1021/jp5085422. Epub 2014 Nov 13.
The equilibrium behavior of ellipsoidal Janus nanoparticles adsorbed at spherical oil/water interfaces was investigated using dissipative particle dynamics simulations. Several phenomena were documented that were not observed on similar simulations for planar oil/water interfaces. The nanoparticles were found to yield isotropic, radial nematic phases, and axial nematic domains, depending on the nanoparticle characteristics (aspect ratio and surface chemistry), particle density at the interface, and droplet properties (curvature of the interface, and surprisingly, liquid type). When adsorbed on water droplets, the nanoparticles with high aspect ratio and few nonpolar beads on their surface can show two preferred orientation angles. Only one equilibrium orientation was found for such nanoparticles adsorbed on oil droplets. These observations might help explain a discrepancy previously reported between experimental and simulation results concerning the preferential orientation of particles at liquid-liquid interfaces. Different driving forces are responsible for the phenomena just summarized, including nanoparticle-nanoparticle and nanoparticle-solvent interactions, nanoparticle density at the interface, and droplet curvature via the Laplace pressure. The simulation results we present could be useful for engineering Pickering emulsions toward practical applications, and perhaps also for guiding new technologies for material synthesis.
使用耗散粒子动力学模拟研究了吸附在球形油/水界面上的椭球形Janus纳米粒子的平衡行为。记录了一些在平面油/水界面的类似模拟中未观察到的现象。根据纳米粒子的特性（纵横比和表面化学性质）、界面处的粒子密度以及液滴性质（界面曲率，令人惊讶的是还有液体类型），发现纳米粒子会产生各向同性、径向向列相和轴向向列域。当吸附在水滴上时，表面具有高纵横比和少量非极性珠子的纳米粒子可以显示出两个优选的取向角。对于吸附在油滴上的此类纳米粒子，仅发现一种平衡取向。这些观察结果可能有助于解释先前报道的关于液-液界面处粒子优先取向的实验和模拟结果之间的差异。不同的驱动力导致了刚刚总结的现象，包括纳米粒子-纳米粒子和纳米粒子-溶剂相互作用、界面处的纳米粒子密度以及通过拉普拉斯压力产生的液滴曲率。我们展示的模拟结果对于将皮克林乳液工程化以用于实际应用可能是有用的，也许还可用于指导材料合成的新技术。
