Investigation of polyacrylamide hydrogels using 1-anilinonaphthalene-8-sulfonate as fluorescent probe

The fluorescent intensity of 1-anilinonaphthalene-8-sulfonate (ANS) has been studied in dioxane–water solutions and in polyacrylamide hydrogels. In dioxane–water solutions both static and dynamic quenching of ANS fluorescence by water molecules occurs. In polyacrylamide hydrogels, whether ionic or not, the fluorescence intensity of ANS is always larger than in dioxane–water solutions for the same water content. This does not result from heterogeneities in hydrogels but from a decrease of the efficiency of both static and dynamic quenching. On the one hand, static quenching is reduced because water molecules close to the hydrophilic polymer chains in the gel are in some way bound to the polymer. On the other hand, dynamic quenching is less efficient because the path length for diffusive transport of water molecules is increased in hydrogels as compared to dioxane–water solutions.