Studying on the Effect of Ph on Volume Phase Transition for Composite Hydrogel Using by Fluorescence Technique

Steady-state fluorescence (SSF) technique was employed for studying swelling of poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) composite gels in various 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 was introduced as a fluorescence probe. P(AAm-co-AAc) composite gels dried before using for swelling experiments. Fluorescence intensity of pyranine 4 was monitored during in situ swelling processes of composite gels. It was observed that fluorescence intensity values decreased as swelling is proceeded. Gravimetrical and volumetrical experiments were also performed. 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 shown that swelling time constants, τ decreased and diffusion coefficients, D increased as the pH values are increased.