Study of chemical gelation dynamics of acrylamide in water by real-time pulsed nuclear magnetic resonance measurement

Chemical gelation process of acrylamide monomers in water has been studied by a real-time pulsed nuclear magnetic resonance (NMR) measurement. The temporal change of molecular mobility has been detected by a real-time observation of the spin–spin relaxation time T2. The influence of the concentration of crosslinker and acrylamide on gelation dynamics has been studied, and it becomes clear that these factors have strong effects on the gelation dynamics. The effects of linear polymerization and network formation on the motional state of water have been studied. The formation of three-dimensional cages drastically reduces the mobility of water. In low acrylamide concentration, the results of NMR measurement mainly reflect the state of water. In high acrylamide concentration, on the other hand, they reflect both polymer network and water, and furthermore, in high crosslinker concentration the spatial heterogeneity of gels is observed. In this paper, we demonstrate that a real-time NMR measurement is a useful tool for a direct observation of the temporal change of molecular mobility during polymerization and gelation process.