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 (<0.05 wt%). This unique system can be achieved by a biopolymer hydrogel with tunable inter- and intra-molecular interactions for microstructural robustness and molecular extensibility by the variation of chemical conformations that microstructure breaks up under shear followed by a low molecularly extensible response. Blends of xanthan and konjac glucomannan containing 99.95 wt% water are demonstrated to satisfy these contradictory requirements and formulated as a function of KCl concentrations. A systematic study was performed using shear and extensional rheology and compared to a reference solution of polyethylene oxide (PEO), a well-known, Boger fluid, highlights the role of molecular elasticity in controlling critical rheological properties. Static light scattering (SLS) and simultaneous rheology and small-angle neutron scattering (RheoSANS) are also used to elucidate the equilibrium structure and flow dynamics. The blends exhibit a lower yield stress and extensional resistance with added KCl, which leads to good spray characteristics in contrast to strain-hardening PEO. The results suggest that the inter-molecular attractions between the two gums leading to network formation with appropriate stiffness, that break up readily under shear, and low molecular elasticity are critical molecular design parameters necessary to achieve sprayable, yields stress fluids. [ABSTRACT FROM AUTHOR]