Fast transient fluorescence (FTRF) technique to study swelling of densely and loosely formed gels

A Strobe Master System (SMS) is introduced for studying the swelling of cylindrical densely (DG) and loosely (LG) formed gels. Gels were prepared by free radical copolymerization of methyl (methacrylate) (MMA) and ethylene glycol dimethacrylate (EGDM). Pyrene (P) was introduced as a fluorescence probe during polymerization, and the lifetimes of P were measured using (SMS) during in situ swelling processes. Chloroform was used as a swelling agent. A model is derived for low quenching efficiencies to measure mean lifetimes 〈τ〉 of P, and it was observed that 〈τ〉 values decreased as the swelling proceeded. The Li-Tanaka equation was employed to determined the time constants, τ_c, and cooperative diffusion coefficients, D_c, which were found to be around 400 min and 10^-5 cm²s^-1, respectively. No differences were detected in τ_c and D_c values of DG and LG gels. Quenching rate constants, κ, and the mutual diffusion coefficient, D_m, were measured and found to be around 10⁵ M^-1s^-1 and 10^-10 cm²s^-1 for DG and LG gel samples.