The chemical gelation viewed through a percolation model simulation

Overview & Synopsis

Many papers or reviews present the percolation theory as pertinent to the chemical gelation problem. But most of these studies are related to the critical behaviour of standard bond or site percolation models. Such approaches ignore totally the specific chemical features which allow the large variety of structures and properties exhibited by chemical networks. The ideal would be to have a model able to mimic realistically the chemical gelation process by taking into account the specificities of each chemical system investigated. But then a basic question arises : do the singularities change the universal behaviour ? This study aims to contribute to answer this question in the particular case of the gelation made by stepwise polymerization. In such systems, gelation may be avoided by introducing monofunctional monomers which are killing the cluster growth. This case is examined in this paper and corresponds to a site-bond percolation problem. Phase diagram is established and the different ways to cross the critical line of this diagram are investigated. The results outline the fact that topological constraints applied to the monomer connection may prevent the system from having a universal critical behaviour. Deleting these topological constraints, by giving a fictive mobility to the monomers, allows us to find again a universal behaviour for the system. This work justifies a posteriori experimental studies on the critical behaviour of the chemical gelation run with quenched systems. It also confirms that chemical stepwise gelation and standard percolation belong to the same universality class and illustrates how this model may be modified to be more realistic.