Anisotropic Guest Diffusion in the Delta-Crystalline Host Phase of Syndiotactic Polystyrene: Transport Kinetics in Films with Three Different Uniplanar Orientation of the Host Phase

The sorption and desorption of a guest (1,2-dichloroethane) in syndiotactic polystyrene (s-PS) films, presenting three different kinds of uniplanar orientation (010), (210) or (002) of the nanoporous host delta phase, have been investigated, mainly by Fourier transform infrared measurements. For guest uptake from dilute aqueous solutions (e.g. 50 ppm), the sorption in the amorphous phase is negligible with respect to sorption in the nanoporous crystalline phase. Correspondingly the guest sorption and desorption kinetics are influenced by the orientation of the anisotropic host crystalline phase. In particular, as for the guest diffusivity (D) measured by both sorption and desorption experiments, D(010) <= D(002) < D(unoriented) <= D(210). These results can be rationalized on the basis of previous molecular dynamics simulations, predicting an anisotropic guest diffusion in the delta crystalline phase.