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Novel measurements of the spatiotemporal microstructure of a continuous shear thickening colloidal suspension under shear cessation and reversal using small angle neutron scattering in a 1–2 shear cell are presented for moderate to high Péclet numbers. In the shear cessation experiments from high Péclet shear flow, two-step relaxation mechanism is found. Particles first readily diffuse on a characteristic timescale of single particle Brownian motion, followed by slower relaxation dynamics on a timescale of short-time self-diffusion when caging effects start dominating. In the shear reversal experiment, the unchanged scattering intensity and the quick flip in anisotropic structure around the shear thickened state suggest the persistence of hydroclusters without transitioning through the equilibrium structure, at least in a time resolution of 0.01 s. Access to the time evolution of microstructure provides valuable insights into the spatiotemporal details of interparticle interactions governing colloidal suspension rheology, such as Brownian, hydrodynamic, and nanotribological forces. [ABSTRACT FROM AUTHOR]

In this work, we outline the development of a thermodynamically consistent microscopic model for a suspension of aggregating particles under arbitrary, inertia-less deformation. As a proof-of-concept, we show how the combination of a simplified population-balance-based description of the aggregating particle microstructure along with the use of the single-generator bracket description of nonequilibrium thermodynamics, which leads naturally to the formulation of the model equations. Notable elements of the model are a lognormal distribution for the aggregate size population, a population balance-based model of the aggregation and breakup processes and a conformation tensor-based viscoelastic description of the elastic network of the particle aggregates. The resulting example model is evaluated in steady and transient shear forces and elongational flows and shown to offer predictions that are consistent with observed rheological behavior of typical systems of aggregating particles. Additionally, an expression for the total entropy production is also provided that allows one to judge the thermodynamic consistency and to evaluate the importance of the various dissipative phenomena involved in given flow processes. [ABSTRACT FROM AUTHOR]

Structure-property relationships of alkali-activated aluminosilicate gels are studied using rheology, neutron scattering, solid-state NMR, and TEM to develop a pseudo-ternary state diagram. Empirical gel states are classified by the rheological behavior (sol-gel transition and scaling of storage modulus with aluminum concentration). The state boundaries are compared to alkali-activated materials from the literature including denser binders. This work focuses on two compositions of dilute gels, formulated to specifically quantify the effects of pH and aluminum concentration on gel microstructure and rheology. Gels formulated at constant pH of 12.5 show a change in morphology and silicon coordination, but consistent mass fractal dimension as aluminum concentration is increased. This microstructural behavior contrasts the characterization of gels previously formulated with a variable pH (range 3–11) which is dependent on aluminum concentration. These results inform the complicated interactions in the polycondensation reaction of alkali-activated binders and lead to a state diagram which unifies many structure-property observations reported for these materials. Structure-property relationships for two formulations of N-A-S-H gels are compared and plotted in a pseudo-ternary state diagram which includes other compositions of N-A-S-H gels and alkali-activated binders from the literature, shaded according to the scaling of the storage modulus where applicable. [Display omitted] [ABSTRACT FROM AUTHOR]