Research Initiation Award Grant - Colloidal Mixtures: Microstructure and Mechanics

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The Research Initiation Award entitled - Colloidal Mixtures: Microstructure and Mechanics - investigates mixtures of colloidal particles which are used in a wide array of commercial and industrial products. In many applications, the colloidal suspensions transform between fluid and disordered solid states when parameters such as the colloidal volume fraction and the strength and nature of the colloidal interactions are varied. Understanding the connection between the microscopic and macroscopic properties remains a central challenge for the field of colloid science. X-ray photon correlation spectroscopy (XPCS) has emerged as a technique uniquely suited for revealing the salient nanometer-scale structural dynamics in glassy colloidal suspensions. This project combines XPCS with rheometry in new ways to make direct connections between the microscopic dynamics and rheology of mixtures of nanocolloidal suspensions.The project will consist of four stages: 1) By investigating the consequences of a bimodal size distribution combined with intrinsic short-range attractions between colloids, the experiments will open a new avenue for controlling suspension phase behavior and rheology. 2) The experimental characterization of the microstructure, dynamics and mechanical response in these colloidal materials will provide a series of benchmarks for rigorous testing of different theories. 3) The developed theory of predicting the flow properties from measured microstructures will result in a microscopic understanding of the rheological properties. Coupled with the knowledge of how experimentally controlled variables affect these microscopic parameters opens up avenues for controlling the flow properties of dense suspensions and gels. 4) Techniques will be developed at Argonne National Laboratory to study the dynamics of colloidal gels and this will be extremely useful in studying the dynamics of a variety of soft condensed matter systems and will be of interest to a number of other users at ANL. The project is expected to lead to a fundamental and microscopic understanding of dynamics of condensed matter systems and to revolutionize processing of such systems by control of their rheology and flow properties.