Self-diffusion of macromolecules and macroassemblies in curdlan gels as examined by PFG-SE NMR technique

Curdlan gels show a potential use as drug delivery biomaterials. The transport properties in curdlan gels were examined by measuring the self-diffusion coefficients (Ds) of water, polyethylene glycols (average molecular weight of 1000 and 3350), and cetylpyridinium chloride micelles, using NMR Pulsed-Field-Gradient technique. The curdlan concentration was varied from 0 to 10 w/w% whereas the temperature was changed between 25 and 45 °C. The behavior of this system shares several features with other polymer gels that were already characterized. It is shown that the self-diffusion coefficient of gel-entrapped solutes can be easily modulated by the gel concentration, and the temperature. It is shown that the reduction of relative diffusion coefficients (Ds/Ds0 where Ds0 is the self-diffusion coefficient in water) is more pronounced for larger solutes, a feature related to the mesh size of the gels. The influence of the temperature on Ds of the investigated solutes could be described by an Arrhenius-type equation. The activation energy associated to the diffusion was in the same order as those reported in diluted or semi-diluted gels. For a given solute, there was no significant difference between the activation energy associated to the diffusion of the solute free in aqueous solution or incorporated in curdlan gels. This finding suggests the lack of appreciable interactions between the solutes and curdlan polymer. The diffusion data were analyzed according to the diffusion models proposed by Cukier (Macromolecules 17 (1984) 252) and Petit et al. (Macromolecules 29 (1996) 6031) and the extracted parameters are discussed.