Charge screening effects on filament dynamics in xanthan gum solutions

We experimentally investigate the filament dynamics of non-Newtonian drops falling under gravity through air, and report the effects of semi-dilute concentrations of the polyelectrolyte polymer xanthan gum mixed in 80:20 glycerol/water with varying concentrations of potassium chloride (KCl). We find that the addition of 780 ppm xanthan gum to the glycerol/water solvent dramatically increases the drop length just before pinch-off, by two orders of magnitude. This length is decreased by as much as an order of magnitude with the addition of KCl. The qualitative dynamics of bead formation on the filament is also very sensitive to added salt. These experimental observations are related to well-known changes in the molecular structure of xanthan gum due to charge screening effects. (c) 2006 Elsevier B.V. All rights reserved.