Clustering, glass transition and gelation in a reactive fluid

We study the dependence of the dynamics on the size of particle clusters that grow by stepwise aggregation in a two-component reactive mixture. The data reveal the cluster property involved in the glasslike arrest and its quantitative link with the structural relaxation time. Specifically, we measured the number-average cluster size X(n)-i.e., the average number of bonded monomers per molecule-and, independently, the characteristic time tau for decay of the photon correlation function, throughout the reaction. We find that x(n) diverges as the system freezes at the glass transition, x(n) and tau being exponentially related. The comparison with the gel transition that occurs at the divergence of the weight-average cluster size provides evidence that the two transitions are associated to distinct properties of the same underlying clustering process.