Capillary Assembly\nof Anisotropic Particles at Cylindrical\nFluid–Fluid Interfaces

Abstract

The unique behavior of colloids at liquid interfaces\nprovides exciting\nopportunities for engineering the assembly of colloidal particles\ninto functional materials. The deformable nature of fluid–fluid\ninterfaces means that we can use the interfacial curvature, in addition\nto particle properties, to direct self-assembly. To this end, we use\na finite element method (Surface Evolver) to study the self-assembly\nof rod-shaped particles adsorbed at a simple curved fluid–fluid\ninterface formed by a sessile liquid drop with cylindrical geometry.\nSpecifically, we study the self-assembly of single and multiple rods\nas a function of drop curvature and particle properties such as shape\n(ellipsoid, cylinder, and spherocylinder), contact angle, aspect ratio,\nand chemical heterogeneity (homogeneous and triblock patchy). We find\nthat the curved interface allows us to effectively control the orientation\nof the rods, allowing us to achieve parallel, perpendicular, or novel\nobliquely orientations with respect to the cylindrical drop. In addition,\nby tuning particle properties to achieve parallel alignment of the\nrods, we show that the cylindrical drop geometry favors tip-to-tip\nassembly of the rods, not just for cylinders, but also for ellipsoids\nand triblock patchy rods. Finally, for triblock patchy rods with larger\ncontact line undulations, we can achieve strong spatial confinement\nof the rods transverse to the cylindrical drop due to the capillary\nrepulsion between the contact line undulations of the particle and\nthe pinned contact lines of the sessile drop. Our capillary assembly\nmethod allows us to manipulate the configuration of single and multiple\nrod-like particles and therefore offers a facile strategy for organizing\nsuch particles into useful functional materials.