A POPULATION-DISTRIBUTION MODEL FOR THE ALIGNMENT OF NEMATIC LIQUID-CRYSTALS

In polymer aligned liquid crystal cells, a surface layer exists. In th is surface layer the in-plane distribution of the mesogens, the shape of the mesogens, and their average angle with the surface determine th e pretilt angle in the bulk of the sample. A model to incorporate thos e effects has been proposed. This model gives quantitative agreement w ith a number of experiments for thick cells, where the optical effects of the surface layer can be neglected. By introducing a linear variat ion of the optical axis through the surface layer we get qualitative a greement between the model and the pretilt found in thin cells. The th ickness of the surface layer is of the order 0.1-1.0 mum.