Liquid crystal formation and rheological study in aqueous blends of xanthan/acacia gum

In this work, the liquid crystalline (LC) phase in an aqueous acacia/xanthan gum (AG/XG) system was determined by optical and rheological analyses. The experimental results indicate that with moderate blending ratios, the AX-W tertiary system, in which AG and XG were simultaneously dissolved together in H2O, formed a dispersed LC structure while the A-XW tertiary system, in which AG was mixed with ready aqueous XG, formed a strand-like LC structure. This morphological difference is attributed to the possibility of AG/H2O coupling to form a continuous non-LC domain; this coupling was not observed in AG/XG blends with extremely low (10/10), or high (55/10) ratios. A schematic model that explains the morphological results is proposed. Measurements of viscosity verify the morphological observations. AG/H2O coupling forms a lubricant with near-Newtonian behavior. The power law indices increased with the AG content to 45 wt% for both AX-W and A-XW systems. In contrast, increasing the XG content promoted the non-Newtonian behavior of the blends. Finally, aqueous XG with 10 wt% solid content acted as a strong gel, which was insensitive to variation in temperature. However, the addition of AG to such blends reduced the viscosity and increased their sensitivity to temperature.