Swelling of heterogels in good solvents; A fast transient fluorescence study

The swelling of disc-shaped heterogels were studied using Fast Transient Fluorescence Technique (FTRF). In this technique the photo multiplier tube (PMT) is gated or strobed by avoltage pulse that is synchronized with the pulsed light source. Disc-shaped heterogels were prepared by combination of methyl-methacrylate (MMA) and styrene (S) with ethylene glycol dimethacrylate (EGDM) as a crosslinker agent in the presence of 2,2'-azobisisobutyronitrile (AIBN). Pyrene (P) was introduced as an extrinsic floroprobe during polymerisation. Seven different gels were prepared at 70 degrees temperature in constant (1.5 % v/v) EGDM content with various combinations of MMA and S contents. Lifetimes of P were measured in-situ swelling processes of heterogels in good solvents to determine the relationship between the diffusion and solvent quality. Chloroform and toluene were chosen as swelling agent which have the solubility parameter, δ of 19 and 18.2 (MPa)1/2 respectively. These values of the solvents are sufficient to make the chloroform and toluene good solvent for PMMA (δ p=19 (MPa)1/2) and PS (δp=18.5 (MPa)1/2), respectively. An equation is derived for low-quenching efficiencies to interpret the behaviour of the lifetime of P during swelling. Li-Tanaka equation was employed to determine the swelling rate constant and the cooperative diffusion coefficients in heterogel and they were found to be strongly correlated with the chosen solvent and the polymeric material in the heterogel system