Connecting nanoscale structure and dynamics to rheology and flow of glassy nanocolloidal suspensions

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1336166PI: LehenyX-ray photon correlation spectroscopy, in conjunction with other scattering techniques and rheometry, is used to understand microstructural dynamics underlying rheology and flow of three different concentrated nanocolloidal systems: binary mixtures of silica nanocolloids with short-range attractive forces; a depletion-induced colloidal gels; and a nanoemulsion. Data obtained for these systems will provide tests for the generality of the theories for gel-fluid and glass-fluid transitions in colloidal systems and insights into their nonlinear rheology.When sub-micron to nanoscale particles are suspended in a liquid, the resulting composite material, or colloid, can adopt properties of a fluid, a solid, or something in between. In many cases, seemingly subtle changes in the characteristics of the material can dramatically alter its mechanical rigidity and flow behavior. This sensitivity creates both a scientific challenge and an opportunity for designing suspensions with properties tailored for specific applications. Indeed, such control is crucial to a vast range of technologies from 3D printing to food processing and drug delivery. This grant supports a novel avenue of investigation into colloidal suspensions that promises to expand the strategies available for controlling their rigidity and flow, particularly by elucidating the unique properties of suspensions of two sizes of particles with a tendency to stick together that can be tuned. A key feature of the experimental program will be the application of a new x-ray technique that enables unprecedented resolution of the slow microscopic motions in soft materials at lengths as small as a molecule. The development of these x-ray methods for investigating materials under deformation and flow will have impact far beyond the planned experiments by providing a new tool with application that spans several traditional disciplines including physics, chemical engineering, and the biosciences.