Nowadays, a wide variety of experimental techniques is used to monitor the translational diffusive dynamics in molecular liquid systems. In comparing results from different techniques mention should be paid on the self or collective character of the relaxation mode probed [1][2][3][4].
It is a widely held view, for example, that Nuclear Magnetic Resonance (NMR) gives information on diffusive single particle correlations, whereas Dynamic Light Scattering (DLS), such as Photon Correlation Spectroscopy (PCS), can allow to test the cooperative nature of molecular diffusion. PCS is a time-domain technique which has been extensively employed in the study of the dynamical behaviour of many systems including liquids, supercooled liquids, aqueous solutions to name a few. The utility of this technique has been greatly extended during the last few years by the introduction of logarithmic time base correlators and crosscorrelation methods based on fiber optics. The information on the collective diffusion coefficient, extracted from the PCS data, when compared with those on the self diffusion coefficient, extracted by NMR spectroscopy, can give relevant information on the repulsive or attractive nature of the intramolecular forces between the basic units of the polymer and the interraolecular forces among the hydrated polymeric chains.