Modification of xanthan solution properties by the cationic surfactant DTMAB.

The interactions between xanthan gum (XG) and dodecyltrimethylammonium bromide (DTMAB) are studied by static and dynamic light scattering, microrheology and viscometry within the overlapping regime of aqueous xanthan solutions. In the absence of salt mixing with surfactant transforms the complex fluid of interconnected xanthan chains into diffusing aggregates because of the reduction of the polysaccharide's effective charge and the introduction of hydrophobic units. In the presence of salt the effect of complexation is weaker. Mixing the two components while XG is in its denatured state results to a network with reduced interchain connections. Linear (microrheological) and nonlinear (steady shear) viscoelastic experiments show that there is a significant compromise of the viscoelastic moduli which is remarkably more intense when mixing DTMAB with XG in its denatured state. These findings prove that xanthan's viscoelastic and morphological properties may be tuned by addition of surfactants and that the conformational state of XG during complexation is a defining parameter.