GAS-TRANSPORT OF HYDROCARBON GASES THROUGH SMECTIC-A LIQUID-CRYSTALLINE ELASTOMERS

The transport behaviour of hydrocarbon gases through liquid-crystalline (l. c.) elastomers is investigated. For different l. c, elastomers exhibiting the smectic-A phase structure, diffusion and permeation coefficients and solubilities are measured as a function of temperature. The behaviour al the smectic-A to isotropic phase transformation is discussed and the permeabilities of propane through different l. c. membranes are compared with respect to their network type, spacer length and end group of the mesogens. In methacrylate networks with high phase transformation enthalpies a discontinuous behaviour is observed at the smectic to isotropic phase transformation temperature T(c), as expected for a first-order phase transformation. Depending on the chemical consitution of the membrane the l. c. state can reduce or improve the gas transport compared to the isotropic state. With increasing flexibility of the membrane system - caused by a more flexible network, longer spacer or longer end group - the permeabilities exhibit significantly higher values. For all elastomers an increase of the ideal selectivities is observed in the smectic-A phase.