The effect of swelling on the crystallinity of freeze/thaw polyacrylonitrile gel analyzed by WAXS technique

Abstract Wide-angle X-ray scattering measurements were performed for the freeze/thawed polyacrylonitrile gels on which various swelling experiments were conducted, and aging periods of 10 days and 10 months were imposed. A characteristic Bragg reflection corresponding to the polyacrylonitrile crystallite was observed and was attributed to the crosslink domains formed during the freezing and thawing cycles. The relative amount of crystalline structure ( X c ) and apparent crystalline grain size were determined for the swollen gels by decomposing the acquired X-ray spectrum into the reflection peaks of the (100) and (020) planes and the amorphous halo. As a result, both the grain size and X c decreased with increasing swelling ratio, implying that the crosslink domain size decreased with the progress of gel swelling. The X-ray spectrum observed for the gel after 10 months of aging was different from that of 10 days aging, implying that the crystalline aggregations among the polyacrylonitrile chains evolved and stabilized the crosslinks during aging. A promising program for freezing and thawing was presented with reference to the molecular process that takes place during the evolution of chain aggregation in order to manage the aging effect in the practical use of the gel.