Swelling and drying process in ionic hydrogels for low and high pH using fluorescence technique

Abstract

Steady-state fluorescence (SSF) technique was employed for studying swelling and drying of poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) composite gels for low and high pH. Disc shaped composite gels were prepared by free-radical crosslinking copolymerization of P(AAm-co-AAc). N, N’-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and initiator, respectively. Pyranine 4 (4sPy) was introduced as a fluorescence probe. P(AAm-co-AAc) composite gels dried before using for swelling experiments. Fluorescence intensity of 4sPy was monitored during in situ swelling and drying processes of composite gels. It was observed that fluorescence intensity values decreased as swelling is proceeded. Li-Tanaka equation was used to determine the swelling time constants, τ and cooperative diffusion coefficients, D from intensity variations during the swelling processes. It was also observed that fluorescence intensity values increased as drying is proceeded. Gravimetrical and volumetrical experiments were also performed. It was shown that swelling time constants, τ decreased, diffusion coefficients for swelling process, DF increased and diffusion coefficients for drying process DG decreased as the pH values are increased.