POLYELECTROLYTE BEHAVIOR OF DILUTE XANTHAN SOLUTIONS - SALT EFFECTS ON EXTENSIONAL RHEOLOGY

The flow behaviour of xanthan, a biological polyelectrolyte, has widel y been reported to be complex, and unlike that of synthetic polyelectr olytes. Most studies have been confined to xanthan concentrations abov e 0.02% w/w. Using a highly sensitive opposed-jets technique, we have now measured salt concentration effects on the extensional flow behavi our of xanthan in aqueous solution at a concentration of 0.01% w/w. At this low concentration xanthan behaves precisely as expected for a 'n ormal' polyelectrolyte, collapsing from an extended worm-like conforma tion to a more compact coil. We suggest that the behaviour at higher x anthan concentrations arises from a disorder-order transition due to i ntermolecular effects. Copyright (C) 1996 Elsevier Science Ltd.