RADIOWAVE DIELECTRIC-PROPERTIES OF XANTHAN IN AQUEOUS-SOLUTIONS

The dielectric and conductometric properties of aqueous solutions of x anthan, an ionic polysaccharide consisting of a linear cellulosic back bone 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 GH z by means of frequency domain dielectric spectroscopy, at different p olyion concentrations and at two different temperatures, above room te mperature, 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, a nd the parameters have been discussed on the basis of currently accept ed dielectric relaxation theories of polyelectrolyte solutions. For th e majority of the polyion concentrations employed, a semidilute regime occurs and the two observed dielectric relaxation are ascribed to cou nterion fluctuations on two different scale lengths, the first associa ted to the polymer contour length and the second one to an average dis tance between charged groups of adjacent polyions. Moreover, these mea surements suggests that a conformational transition occurs at temperat ures above 40 degrees C with the consequent formation of an extended t hree-dimensional network. This transition results in a particular beha vior of the dielectric relaxation on the polymer concentration.