Special CPM seminar

Self-assembly of colloidal particles at nematic interfaces

Mohamed Gharbi

Department of Physics & Astronomy
University of Pennsylvania

Colloidal particles trapped at the interface between two immiscible fluids usually display various bidimensional phases depending on the competition between direct and capillary interactions. In addition, the physics of colloids confined in a nematic cell have been thoroughly investigated in recent years. The structures formed by embedded solid spheres strongly depend on the nematic elasticity, the nematic topological defects and the anchoring at interfaces. Here, I examine the behavior of spherical solid particles at nematic liquid crystal (NLC) interfaces with different geometries. First, I will detail the phase behavior of beads with strong homeotropic anchoring at an air-NLC interface. Depending on their area density, the nematic thickness, the anchoring, and the confinement conditions, I found that colloids spontaneously form various structures. Subsequently, I will report the behavior of silica beads at more complex NLC interfaces. By controlling the geometry of the interfaces and the colloids density with microfluidic techniques, several structures have been observed. Finally, I will review how the competition between anchoring conditions, liquid crystal elasticity, and the topology of the curved surface is responsible for long-range interactions and the formation of new ordered structures.