Critical exponents and fractal dimension at the sol-gel phase transition via in situ fluorescence experiments

Changes in solvent viscosity due to gel formation dramatically enhance the fluorescent yield of aromatic molecules. This effect is used to study the gelation of methyl methacrylate and ethylene glycol dimethacrylate as a function of time, at various temperatures, cross-linker concentrations, and toluene contents. The results are interpreted in view of percolation theory. The gel fraction and average cluster size exponents are found to be beta=0.42+/-0.03 and gamma=1.70+/-0.02, in excellent agreement with percolation results. The fractal dimension of the incipient cluster is determined to be 2.5+/-0.2. The behavior of the time derivative of the fluorescence intensity is shown to satisfy finite size scaling. [S1063-651X(98)07611-9].