Can the isotopic H <-> D substitution affect the conformational propertiesof polymeric aqueous solutions? The poly(ethylene oxide)-water case

This paper deals with measurements, performed using dynamic light scatterin g (photon correlation spectroscopy (PCS) and Raman spectroscopy) and small angle neutron scattering (SANS), on solutions of poly(ethylene oxide) (PEO) in water and heavy water. The joint employment of these techniques allows us to carry out a side by side comparison between the PEO/H2O and the PEO/D 2O systems. The coil conformation dependence on temperature and concentrati on is studied; in particular, the hydrodynamic radius, as evaluated from th e diffusion coefficient at infinite dilution using PCS, and the gyration ra dius, evaluated by SANS, are determined at different temperatures, i.e. as a function of the solvent quality On the other, the study of the Raman D-LA M spectral contribution furnishes valuable information on the structural ar rangement of the molecules. The experimental findings clearly show from the different diffusive propert ies of polymer chains that the isotopic substitution affects the hydrodynam ic radius behaviour with temperature, and from the Raman scattering results that it induces a lowering of the conformational order degree. Such findin gs provide evidence of the different behavioural properties of macromolecul es in H2O and D2O, and could be relevant for the areas of research in which the deuterium labelling technique is commonly employed.