Diffusion of Probe Molecules in Polymer Gels as Observed by Fluorescence Quenching Techniques

Material transport and diffusion-controlled reaction kinetics in polymer gels are discussed on the basis of a phenomenological model. The model assumes that molecules diffuse freely within pores, while their long-range transport is described as pore hopping or diffusion in an effective medium with a low diffusion coefficient. Recent experiments by Masuda et al. ( J. Am. Chem. Soc. 2001, 123, 11468−11471) on fluorescence quenching in aqueous solutions of hyaluronan are analyzed on the basis of the present theory. It follows that the conventional mesh size of the polymer network may only poorly characterize obstruction to diffusion. New experiments are suggested to clarify this point.