Effect of molecular conformation on the surface properties of polyelectrolyte solutions : xanthan gum model studies

Graduation date: 1987A commercially important polyelectrolyte, xanthan, was chosen for\ud a systematic analysis of the relationship between molecular\ud conformation and surface properties. In the first study the effects\ud of ionic strength, xanthan concentration and temperature on the\ud xanthan molecular conformation were investigated by potentiometric\ud titration. The effects of the same factors and of the degree of\ud ionization on the surface tension of xanthan solutions were then\ud analyzed by the drop weight and the Wilhelmy plate methods.\ud Potentiometric titration studies showed that the ordered xanthan\ud conformation is stabilized mainly by hydrogen-bonds which can be\ud disrupted by increasing the electrostatic potential of the molecule or by increasing the solution temperature. Adding salt or increasing\ud the xanthan concentration did not affect the secondary structure.\ud Surface tension studies showed that the random coil is more\ud surface active than the helix xanthan structure. The rate of xanthan\ud adsorption at the interface of the random coil is also faster than\ud that of the helix structure. Surface tension was also shown to be\ud dependent on the electrostatic potential of the polyelectrolyte.\ud Added salt screened the electrostatic repulsive force and therefore\ud decreased the surface tension of xanthan solution