(29b) Molecular Engineering of Thixotropic, Sprayable Fluids with Yield Stress Using Associating Polysaccharides

Molecular engineering facilitates the development of a complex fluid with contradictory requirements of yield stress and sprayability, while minimizing the amount of structuring material. Blends of xanthan (Xg) and konjac glucomannan (Kg) containing 99.95 wt% water are demonstrated to satisfy these contradictory requirements by building structure without substantial molecular elasticity. Comparison of shear and extensional properties against a reference solution of polyethylene oxide (PEO), a well-known, Boger fluid, highlights the role of molecular elasticity in controlling critical rheological properties. Added KCl alters inter- and intra-molecular interactions so as to tune rheological properties. The gum blends exhibit a lower extensional resistance with added KCl, which leads to good spray characteristics in contrast to PEO, which shows strain hardening. These measurements suggest that the inter-molecular attractions between the two gums leading to network formation with appropriate stiffness and low molecular elasticity are critical molecular design parameters necessary to achieve sprayable, yields stress fluids.