Effect of nanoconfinement on kinetics of cross-linking reactions: a molecular simulation study

We have used molecular dynamics simulations to study the effect of nanoconfinement on the kinetics of cross-linking reactions. Specifically, a bead-spring model is used to carry out reactive molecular dynamics simulations of the autocatalytic epoxy curing reactions. In this simple model, if two colliding molecules arrive in spatial proximity, they react to form a new bond with a specified probability. The kinetics of the reaction in the bulk was compared with that in a cylindrical pore. Our simulations show that confinement leads to an increase in both the translational mobility of the beads as well as the average displacement undergone by the beads from their initial position to the position of reaction. The net result of these opposing factors is that the rate of curing reaction in the confinement is quantitatively similar to that in the bulk. We also observed heterogeneity of reaction rates in the confined system. As compared to the reaction rate in the bulk, the reaction rate in the first layer near the pore wall is lower, whereas the reaction rate in the central core domain of the nanopore hardly shows any difference from the bulk value except in the high conversion stage. The results suggest that the reaction rate in the confined system relative to the bulk will vary with the relative volume fractions of the first layer near the wall and the central core domain.