Patterns in hybrid nematic liquid-crystal films: topography and topology

Spontaneous pattern formation in hybrid nematic liquid-crystal films on glycerol was studied with both polarized transmission and unpolarized monochromatic reflected light microscopy. These observations reveal that the patterns that are found in 1 to 10-microm-thick films are due to a combination of film topography, gradients in film thickness that act as an aligning field, and topology, connectivity requirements on the vector field. The patterns studied include cellular patterns, disclinations connected by 2pi-walls, and 2pi-walls that narrow to a point at the edge of the films.