Nanogel formation by intrachain radiation-induced cross-linking. Simulation and experiment

Nanogel formation by intrachain radiation-induced cross-linking is described. The origin of dispersive kinetics observed in pulse radiolysis experiments and the influence of cross-linking method on nanogel structure are studied by the Monte-Carlo simulation. The simulations have been performed on an fcc lattice using the cooperative motion algorithm. The recombination kinetics is studied as a function of the chain length (20-1068 beads) and of the number of radicals generated per chain. It is shown that the radical recombination rate coefficients are time-dependent (dispersive kinetics) and the simulation results can be fitted using single "stretched exponential" (KWW) function for two radicals per chain and a sum of two KWW functions for a larger number of radicals. The nanogel structure (radius of gyration and loop lengths, related to the resistance of nanogels to scissions) has also been studied. It is found that in the case of instant radical generation, the increasing number of radicals leads to formation of smaller and smaller loops. Results of the simulations are compared with the pulse radiolysis experiment on poly(ethylene oxide) using a suitable scaling of MC time and unit length, and a good agreement is obtained.