THE EFFECTS OF THE PACKING STATE OF POLYPEPTIDE α-HELIX CHAINS ON THE SORPTION AND PERMEATION BEHAVIORS OF THE MEMBRANES

Abstract

Three types of membranes of poly (γ-methyl D-glutamate) (PMDG), membrane A, B and C, were cast from 2% PMDG-ethylene dichloride solution under the different conditions. The membrane A was obtained by vacuum drying of the solution at 25°C for about 2 hrs. The membrane B and C were prepared by air-drying of the solution at 25°C for 3 days and 30 days, respectively. Sorption behaviors of these membranes could be described well by a dual sorption model which have been used effectively for gas-glassy polymer systems. The temperature dependence of Henry's law sorption parameter, kD, of membrane B and C had an inflection point at the second order transition temperature of the side chain. On the other hand, kD of membrane A linearly increased with increasing temperature. The Langmuir capacity term, C′H, of membrane A was considerably larger than those of B and C. The permeation behavior of membrane A involved the convectional flow, i.e., the permeability coefficient of CO2 through membrane A linearly increased with increasing upstream pressure. On the other hand, the permeation behaviors of membrane B and C could be interpreted by the dual mobility model. As a result, separate diffusion coefficients of CO2 for Henry's law and Langmuir modes, DD and DH, were estimated. It was found that the diffusivity for the Langmuir mode gas in the membranes was relatively high, DH/DD being almost equal to unity. All of these results were ascribed to the difference of the packing state of the α-helix chains in these membranes, which was caused by the different membrane preparation.