Synthesis and monolayer formation of liquid crystal polysiloxanes having a lateral side chain with a perfluoroalkyl chain

Abstract

Liquid crystal polysiloxanes with a lateral 4-(4-cyanophenoxycarbonyl)phenyl 4-(2-perfluoroalkylethoxy)-2-propyleneoxybenzoate side group and a 4-decyloxy-2-propyleneoxy-benzoate hydrocarbon analogue were prepared, and the mesomorphic properties were determined by the microscopic observation and differential scanning calorimeter (DSC) thermogram, and the layer structure of the smectic A phase was characterized by an X-ray diffraction experiment. The introduction of the perfluoroalkyl chain to the polymer remarkably enhances the smectic properties due to the strong fluorophilic interactions around the perfluoroalkyl chain. The effect of the perfluoroalkyl chain on the monolayer formation was studied at the air–water interface. The surface pressure–area isotherms show that the perfluoroalkyl chain enhances the stability of the monolayer versus surface pressure. In the condensed state the cyano group in the side chain is assumed to be anchored on the water surface and the mean axis of the liquid crystal core is approximately normal to the water surface. The monolayers were easily deposited on a hydrophobic glass slide, giving uniform Langmuir–Blodgett (LB) films by the vertical deposition method. The X-ray diffraction results indicate that the perfluorooctyl chain effectively stabilizes the layer structure in the multilayer LB film at room temperature. The side chain monomers also show a similar behavior to the polymers and give uniform LB films on hydrophobic glass slides.