Correlation between rheology of charged particle suspensions and microscopic interactions and dynamics*

Colloidal gels aggregated from charged particles with attractive or repulsive forces form a rigid and fragile network that could easily yield, transforming from a solid to a more prominent liquid-like characteristics under weak external forces. Such materials are promising for applications in everyday life, including battery electrolyte, drug design, enhanced oil recovery, and food products. To improve the efficiency and extent of these applications, the mechanical properties of the colloidal gel such as yielding could be tuned by controlling the surface interaction of individual particles and ionic conditions in the solvent. Consequently, it is imperative to understand the fundamental relationship between the macroscopic properties and microscopic behavior. X-ray photon correlation spectroscopy (XPCS) carried out in conjunction with in situ rheology (Rheo-XPCS) is ideally suited to probe fluctuation dynamics at the relevant length scales (10-300 nm). XPCS measurements of the colloidal gels reveal novel microscopic dynamic features during creep and relaxation thereafter. The yielding transitions observed under applied stresses are consistently correlated with the strain and shear in rheological measurements. The influence on creep response and variations to the correlation function from the addition of salts with different valences to the colloidal gel is also revealed. The results connect the microscopic dynamics of particles to the macroscopic properties of the system establishing new perspectives on understanding dynamic behaviors of the colloid suspension under external forces.