Monitoring small molecule diffusion into hydrogels at various temperatures by fluorescence technique

Steady state fluorescence technique was used to study small molecule diffusion into polyacrylamide (PAAm) gels at various temperatures. Pyranine (P(y)), dissolved in water was introduced as a probe and fluorescence emission (I(p)) from P(y) was monitored during diffusion. Scattered light intensities, I(sc) from PAAm gel was also monitored to observe structural variations during diffusion process. Increase in I(p) intensity was attributed to P(y) diffusion into PAAm gel. On the other hand decrease in I(sc) intensity was interpreted as the variation of the spatial heterogeneities in the system. Li-Tanaka and Fickian models were used to quantify the swelling and diffusion experiments and diffusion coefficients were produced in both cases. Related activation energies were also calculated from the corresponding physical processes.