Aaron W. Levine

Alignment and wetting properties of nematic liquid crystals on plasma-polymerized films

Abstract The polar and dispersive components of the surface energy of nematic liquid crystals were calculated from contact angle measurements on a variety of polymeric films with known surface energies using the Kaelble-Good-Girifalco-Fowkes equation. The orientation of liquid crystals on plasma-polymerized films with a wide range of surface energies was studied. A relationship between the spontaneous spreadability criteria calculated from surface energy and liquid crystal orientation was observed. In general, a negative spreadability coefficient of a liquid crystal on a plasma-polymerized film indicates perpendicular alignment and a positive spreadability coefficient predicts parallel alignment. The measured critical surface energy of the plasma-polymerized films varied widely depending upon the choice of solvent used, and no relationship was observed between this value and liquid crystal orientation.

Enthalpy of Fusion of Nematogens

Abstract The enthalpy of fusion of nematic compounds is an important parameter related to the use of such materials in displays. Since no single material is adequate in nematic range for use in displays, a substantial amount of work is required in preparation and evaluation of mixtures. One valuable method of estimating the nematic range of liquid crystal mixtures is based on the Schroeder-Vanlaar equation,1-5 which related the melting temperature of a solution (Tm ) to the mole fraction, x, of solute of melting temperature T and enthalpy of fusion ΔH, and the gas constant, R.