Photon transmission technique for monitoring formation and swelling of polyacrylamide gels

Abstract

The in situ, real-time photon transmission technique was used to monitor the free radical crosslinking copolymerization of acrylamide and N,N′-methylenebisacrylamide (Bis). Gelation experiments were performed with various Bis contents at various wavelengths. It was observed that the transmitted photon intensity, I tr, decreased dramatically at a certain reaction time, which is attributed to the increase in scattered light intensity, I sc, during the formation of microgels in the system. The increase in I scwas modeled using Rayleigh's equation where the reaction time was found to be proportional to the volume of the microgels. The disc-shaped polyacrylamide (PAAm) gels were dried before use during swelling experiments. Transmitted light intensity, I tr, from the gel increased at initial stages when PAAm gels were immersed in water and then decreased exponentially as the swelling time increased. Decrease in I trwas attributed to the lattice heterogeneities, which might have originated between microgels and holes in the swelling gel. Decrease in I trwas modeled using the Li–Tanaka equation from which cooperative diffusion coefficients, D c, were determined for gels of various Bis contents. It is observed that the D cvalues increased with the Bis content.