MODELS FOR IRREVERSIBLE GEL FORMATION

Many of the physical and chemical properties of gels are determined by the porosity of the underlying molecular network. The build-lip of an infinite network-and even its existence-often depends on irreversible aggregation processes during the earliest stages of structure formati on. The system gels only once the primary structures fill space. Aggre gation and percolation models each describe one limiting situation of such a sol-gel process. The important intermediate stages cannot be tr eated with the same degree of generality. New results for this crossov er regime are presented: it is shown that there is a smooth change of the structural properties and the cluster size distribution when passi ng from the aggregation to the gelation stage. The measured fractal di mension of the clusters changes continuously as one approaches the gel ation transition. Copyright (C) 1996 Published by Elsevier Science Ltd .