Carbon dioxide diffusion and solubility in a polystyrene-polybutadiene block copolymer with a highly oriented lamellar morphology

Abstract

Abstract : Solubility and diffusion coefficients for CO2 in polystyrene polybutadiene (SB) block copolymer films were measured in a pressure decay sorption apparatus at 1 atm over a temperature range of 20 to 90 C. The morphology of the block copolymer specimens consisted of alternating S and B lamellae of approximately 100 angstrom thickness with excellent long range orientation perpendicular to the surface of the 0.02 to 0.05 cm thick films. Diffusion behavior in the copolymer was simulated using homopolybutadiene and homopolystyrene data along with a finite difference model based on the well- ordered morphology. Comparisons of model predictions with the measured values of the effective diffusion coefficient for CO2 in the copolymer revealed that the diffusion coefficient of CO2 in the polybutadiene region of the copolymer was lower than in homopolybutadiene by a factor of 1.9 at 20 C. This difference disappeared at the glass transition temperature of the polystyrene in SB. This temperature-dependent reduction of CO2 diffusion in the polybutadiene regions of the block copolymer results from restrictions on chain motions of the polybutadiene blocks arising from their connection to polystyrene blocks. (aw)