Carbon nanotubes doped liquid crystals: Robust composites with a function of electro-optic memory

This paper describes effect of electro-optic memory in the carbon nanotubes (CNTs) doped liquid crystals (LCs) and recent trends in optimization of these composites for practical use. The memory effect consists in irreversible increase of light transmittance through the homeotropically aligned layers of LC-CNTs composites placed between two crossed polarizers due to the electric field application cycle. The irreversibility of electro-optic response is caused by stabilization of LC planar alignment realized in the electric field by a network of CNTs acting as a spatially distributed aligning surface. This network reveals itself in percolation behavior of electric conductivity of LC-CNTs samples. By using nematic mixtures MLC6608 and MLC6609 from Merck developed for vertical alignment, a number of essential improvements of the LC-CNTs composites are obtained such as a room temperature operation, reduced controlling voltage and switching time. Efficiency of electro-optic memory of these composites was further doubled by doping LC with small amount of chiral agent. The developed samples give real application prospect to the memory type LC-CNTs composites, especially in the information displaying and storage systems based on the LC materials.