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Swelling studies and adsorption of safranin T by acrylamide/maleic acid/methylene-bis-acrylamide based hydrogels

Abstract Swelling studies of an acrylamide/maleic acid/methylene-bis-acrylamidebased hydrogel prepared by free radical polymerization (weight ratio of 90/10/3) are presented. Water penetration mechanism was studied by using two classical definitions, i.e., Crank (FC = Wt/Weq) and Karadag (FK = (Wt-Wo)/Wo), of the water fraction into the hydrogel (F). An anomalous water penetration mechanism (0.5<n<1.0) was obtained by employing both definitions and Buckley equation (F = ktn); however, using the combined Peppas and Sahlin equation (F = k1t1/2 + k2t) pointing out that swelling occurs in two stages: at first controlled by diffusion and relaxation contributions and then defined mainly by the diffusion contribution. Hydrogel was also studied as a system for the adsorption of cationic dye Safranin. Results show that this system perfectly fit to a Langmuir isotherm and the dye adsorption process stops when coverage of all active sites on the hydrogel has been achieved. Interestingly, adsorption process does not seem to be affected even though the hydrogel concurrently suffers the well known collapse phenomenon.