RADIOWAVE DIELECTRIC-PROPERTIES OF XANTHAN IN AQUEOUS-SOLUTIONS

The dielectric and conductometric properties of aqueous solutions of xanthan, an ionic polysaccharide consisting of a linear cellulosic backbone with three-sugar side chains, have been extensively investigated over two frequency ranges, from 1 kHz to 10 MHz and from 1 MHz to 1 GHz by means of frequency domain dielectric spectroscopy, at different polyion concentrations and at two different temperatures, above room temperature, in the range where an order-disorder transition occurs. The dielectric spectra have been analyzed on the basis of two contiguous dielectric dispersions described by a Cole-Cole relaxation function, and the parameters have been discussed on the basis of currently accepted dielectric relaxation theories of polyelectrolyte solutions. For the majority of the polyion concentrations employed, a semidilute regime occurs and the two observed dielectric relaxation are ascribed to counterion fluctuations on two different scale lengths, the first associated to the polymer contour length and the second one to an average distance between charged groups of adjacent polyions. Moreover, these measurements suggests that a conformational transition occurs at temperatures above 40 degrees C with the consequent formation of an extended three-dimensional network. This transition results in a particular behavior of the dielectric relaxation on the polymer concentration.