Neutral Dielectric Anisotropy in a Binary Liquid Crystal Mixture

Andrew Bouchard

A binary mixture of the nematic liquid crystals 5CB and MBBA was used to create dielectric neutrality so that bulk dielectric effects could be removed and surface effects of a liquid crystal mixture could be observed. Samples of the mixture were placed in unaligned cells to test for the Freedricksz transition to see if the sample was indeed dielectrically neutral. Liquid crystal samples were also placed into homeotropic and planar aligned cells and viewed at various electric field voltages under a long distance microscope. All cells produced periodic dynamic surface effects. The unaligned cells showed no signs of having a Freedricksz transition thereby showing that the sample was indeed dielectrically neutral. The homeotropic cell produced static relaxation patterns when voltage to the cell was shut off suddenly. Times of pattern fading seemed to be dependent on the starting voltage of the cell when the electric field was shut off. The planar cell produced loop disclinations with an applied voltage. These disclinations periodically faded into and out of focus when a large enough voltage was applied to the cell. All effects seen were concluded to be surface effects due to the limited focal range and the extreme lack of similarity to other bulk effects seen by other researchers working with the same materials.