Can the isotopic HD substitution affect the conformational properties of polymeric aqueous solutions? The poly(ethylene oxide)-water case

Abstract

This paper deals with measurements, performed using dynamic light scattering (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/D2O systems. The coil conformation dependence on temperature and concentration is studied; in particular, the hydrodynamic radius, as evaluated from the diffusion coefficient at infinite dilution using PCS, and the gyration radius, 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-LAM spectral contribution furnishes valuable information on the structural arrangement of the molecules. The experimental findings clearly show from the different diffusive properties of polymer chains that the isotopic substitution affects the hydrodynamic radius behaviour with temperature, and from the Raman scattering results that it induces a lowering of the conformational order degree. Such findings provide evidence of the different behavioural properties of macromolecules in H2O and D2O, and could be relevant for the areas of research in which the deuterium labelling technique is commonly employed.