(187f) Thermotropic and Side Chain Liquid-Crystal Polymer Membranes for Light Gas and Vapor-Phase Separations

Authors: 
Rabie, F., Virginia Polytechnic Institute and State University


Methods for the synthesis, characterization, and testing of dispersed thermotropic liquid crystalline (LC) membranes for vapor phase separations have been investigated. Polymer/liquid crystalline mixed matrix membranes were prepared with polysulfone and 4-cyano-4-octyliphenyl (8CB) via a solution casting method. The morphology of the polymer as well as phase separation during the casting process are important factors for formation of a well-dispersed liquid crystalline phase. This was investigated by employing optical microscopy, differential scanning calorimetry, and scanning electron microscopy. In order to improve the stability of the liquid crystal, a homogeneous blend membrane of 8CB and polymer was fabricated and tested. It is postulated that the dispersed LC material will improve the separation and permeation abilities as well as the mechanical stability of the pure polymer. Progressive LC concentrations below the critical concentration for LC droplet formation were investigated at different temperatures. Porous membranes can also be used as a support for the formation of LC membranes. A liquid-crystalline thiol possessing 4-cyanobiphenyl as a mesogenic rigid part and mercapto-terminated flexible hexamethylene spacer was grafted onto a butadiene based polymer. The side chain liquid crystal polymer was used as the interacting material for the separation of paraffins/olefins as well as light gases (He, O2, N2, CH4, and CO2). The SCLC with a molecular weight of 2,800 Da improves the overall stability of the membrane. The intrinsic temperature dependent gas separation behaviors of the liquid crystal were also studied. Mixed gas and single gas permeation studies, sorption behavior, and diffusivities of light gases (He, O2, N2, CH4, and CO2) and paraffins and olefins above and below the LC transition temperatures are also reported.