THEORY AND SIMULATION OF GAS-DIFFUSION IN CHOLESTERIC LIQUID-CRYSTAL FILMS

Theory and simulation of the dynamical phenomena that characterizes ga s diffusion in a cholesteric film are presented. A classical mass tran sfer theory for cholesteric liquid crystals was used to construct a mo del that describes the one dimensional transient gas diffusion in a fi lm. The boundary conditions that describe the concentration and orient ation conditions in a gas-liquid crystal surface were obtained using t he Euler-Lagrange equations for surface reorientations. Numerical solu tions to the coupled mass transfer-orientation equations are presented and used to develop a comprehensive view of the phenomena. The main g overning parameters that control gas diffusion in a cholesteric film a re identified. Two different regimes are identified: (i) diffusion lim ited regime, and (ii) orientation limited regime. The diffusion limite d regime is characterized by strong concentration-orientation coupling s, enhanced mass transfer, and up-hill diffusion. The orientation limi ted regime is characterized by weaker concentration-orientation coupli ngs, and weaker mass transfer enhancements. Conditions that lead to en hanced gas absorption are identified, characterized, and explained in terms of the orientational contribution to the mass flux. Conditions t hat lead to the uncoiling of the cholesteric helix into a nematic orde ring are identified, and the kinetics of the phase transformation is c haracterized.