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Scientific questions surrounding the shear-dependent microstructure of carbon black suspensions are motivated by a desire to predict and control complex rheological and electrical properties encountered under shear. In this work, direct structural measurements over a hierarchy of length scales spanning from nanometers to tens of micrometers are used to determine the microstructural origin of the suspension viscosity measured at high shear rates. These experiments were performed on a series of dense suspensions consisting of high-structured carbon blacks from two commercial sources suspended in two Newtonian fluids, propylene carbonate and light mineral oil. The shear-induced microstructure was measured at a range of applied shear rates using Rheo-VSANS (very small angle neutron scattering) and Rheo-USANS (ultra-small angle neutron scattering) techniques. A shear-thinning viscosity is found to arise due to the self-similar break up of micrometer-sized agglomerates with increasing shear intensity. This self-similarity yields a master curve for the shear-dependent agglomerate size when plotted against the Mason number, which compares the shear force acting to break particle-particle bonds to the cohesive force holding bonds together. It is found that the agglomerate size scales as R g , agg ∼ M n − 1 . Inclusion of the particle stress contribution extends the relevance of the Mason number to concentrated suspensions such as those relevant to the processing of carbon black suspensions for various applications. [ABSTRACT FROM AUTHOR]

In situ measurements are an increasingly important tool to inform the complex relationship between nanoscale properties and macroscopic material measurements. Knowledge of these phenomena can be used to develop new materials to meet the performance demands of next generation technologies. Conductive complex fluids have emerged as an area of research where the electrical and mechanical properties are key design parameters. To study the relationship between microstructure, conductivity, and rheology, we have developed a small angle neutron scattering (SANS) compatible Couette rheological geometry capable of making impedance spectroscopy measurements under continuous shear. We have also mounted this geometry on a commercial strain controlled rheometer with a modified forced convection oven. In this manuscript, we introduce the simultaneous measurement of impedance spectroscopy, rheological properties and SANS data. We describe the validation of this dielectric RheoSANS instrument and demonstrate its operation using two systems—an ion gel comprising Pluronic® surfactant and ionic liquid, ethyl-ammonium nitrate, and poly(3-hexylthiophene) organogel prepared in a mixture of hexadecane and dichlorobenzene. In both systems, we use this new measurement capability to study the microstructural state of these materials under two different protocols. By monitoring their dielectric rheology at the same time as the SANS measurement, we demonstrate the capacity to directly probe structure-property relationships inherent to the macroscopic material response. [ABSTRACT FROM AUTHOR]

Colloidal gels exhibit time-dependent bulk properties. However, the processes and mechanisms by which aging occurs are poorly understood, which complicates the prediction of macroscopic behavior in these systems. Using a model, thermoreversible, adhesive hard sphere system consisting of octadecyl-coated silica nanoparticles dispersed in tetradecane, rheological aging is quantitatively related to structural aging. By simultaneously measuring the bulk properties and gel microstructure using rheometry and small angle neutron scattering, respectively, we show a one-to-one correspondence between the time-dependent storage modulus and the microstructure, and further, that this correspondence is independent of the gel's thermal and shear history. At the working volume fraction, the gel is homogeneous and, unlike phase-separated gels, aging behavior is not due to heterogeneous coarsening. Instead, the results presented here are consistent with homogeneous, local particle rearrangements as the mechanism of rheological aging. By establishing a quantitative and predictive relationship between the underlying microstructure and bulk mechanical properties, the results of this study may be (1) industrially relevant to products that age on commercially relevant timescales, (2) applicable to other dynamically arrested systems, such as metallic glasses, and (3) valuable in the design of new materials. [ABSTRACT FROM AUTHOR]

The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and timeresolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropic microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the "Delaware-Rutgers" rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response. [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]

Highlights: [•] We study the formation of nanovesicles of cationic surfactant DEEDMAC. [•] A method to determine nanovesicle volume fraction is demonstrated. [•] The method is verified by neutron scattering measurements. [ABSTRACT FROM AUTHOR]