DILUTE-SOLUTION DYNAMIC VISCOELASTIC PROPERTIES OF XANTHAN POLYSACCHARIDE

The frequency dependences of the storage and loss shear moduli, G' and G'', of dilute solutions of highly purified xanthan polysaccharide we re measured at 20.0-degrees-C using the Birnboim-Schrag multiple-lumpe d resonator. The frequency range was 150-8000 Hz and the concentration range was 0.1-0.4 g/l. Three solvents were used, one of which contain ed 75% by weight glycerol to increase the solution viscosity. Measurem ents of oscillatory flow birefringence were also made in one solvent o ver the frequency range from 1-630 Hz and agreed well with the viscoel astic data in the range of overlap. The intrinsic viscosity in both wa ter and 25%/75% water/glycerol (with 0.085 mol/l sodium chloride) was determined as 5200 ml/g. The frequency dependences of G' and G'', extr apolated to infinite dilution, could be fitted to a hybrid model for s emiflexible rods which was modified to take into account a moderate de gree of molecular weight distribution (M(w)/M(n) = 1.4). From the expe rimental data the persistence length of the native xanthan was estimat ed at 500-800 nm and Young's modulus of the rod, modeled as a homogene ous body, was calculated to be about 2 X 10(9) dyn/cm2.