W. G. Pritchard Lab Seminar: 4:00-5:00 PM, 317 Boucke Building

	          **Monday December 9, 2002**
	
Dielectric Measure of Polyelectrolyte Charge and Interaction with Water

Ralph H. Colby

Department of Materials Science and Engineering
Penn State University

Abstract:

Using the dielectric strength and relaxation time of a high frequency 
(1 MHz - 1 GHz) dielectric relaxation, we estimate the effective charge on
polyelectrolytes and their net thermodynamic repulsive interaction with
solvent. The method relies on the model of Ito and coworkers, who have
demonstrated that this relaxation is due to polarization of free counterions
on the scale of the correlation length. The utility of this method is
demonstrated for semidilute aqueous solutions of the sodium salt of several
sulfonated polyelectrolytes of varying charge and strength of repulsive
interaction with water, with no added salt. We find that, at high
concentrations, as concentration is increased the effective charge of
strongly charged polyelectrolytes always increases, as previously observed
in conductivity and osmotic pressure measurements. The effective
polymer-solvent repulsion increases in direct proportion to the effective
charge on the polyelectrolyte chains. This proportionality means that,
although the additional charge would increase the contour length of the
chain, the increase in repulsion between solvent and polymer offsets this
effect, making the contour length of the chain essentially independent of
polyelectrolyte concentration. This then explains why the correlation length
of semidilute polyelectrolyte solutions fortuitously agrees with simple
scaling predictions.


    NOTE SPECIAL TIME AND PLACE: Mon 4:00-5:00, 317 Boucke