UNUSUAL BEHAVIOR OF WATER-SOLUBLE POLYELECTROLYTE MACROMOLECULES SHOWN BY QELS STUDY - IS IT A PROPERTY OF HYDROPHOBIC BACKBONES

Using QELS technique we studied the dynamic aspects of a synthetic flexible polyelectrolyte compound in aqueous solutions. By monitoring the ionic strength from very small to high values, we reached two major conclusions. First, in the absence of added electrolyte(s), the polyions are in ≪highly≫ expanded conformation; the dynamics are characterized by two fluctuation modes: cooperative and long range fluctuations. The addition of NaCl introduces a ≪sharp≫ and a priori unusual change. The solute macromolecules experience a non gradual change in their conformation, which is directly reflected in their dynamics. The mutual diffusion coefficient, deduced from the only existing decay rate for the correlation function, does not reflect any observable variation with polymer or salt concentration (cP and cS respectively), for the values we scanned. We attribute this phenomenon to the rising of hydrophobic interactions, once the shielding of the electrostatic interactions becomes effective at sufficiently high ionic strengths, owing to the hydrocarbon nature of the polyions.