SGER: Structure and Phase Behavior of Charged and Polymer-Containing Colloidal Dispersions

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Wu, JianzhongU of Cal - Riverside "SGER: Structure and Phase Behavior of Charged Polymer-Containing Colloidal Dispersions"Colloidal dispersions are broadly applied in the fabrication of modern materials such as photonic crystals, catalysts, membranes, porous electrodes, and advanced ceramics. These applications require theoretical guidelines for understanding interfacial and thermodynamic phenomena such as colloidal stability, structural properties, and phase behavior that depend on multiple parameters, including particle size and concentration, charge density, ionic strength, properties of solvent and dissolved polymers, and confining geometry. To meet this requirement, the present research combines theoretical methods from statistical mechanics with small angle neutron scattering (SANS) experiments to establish a unified molecular framework for quantitative description of structural and thermodynamic properties of charged and polymer-containing colloidal systems. This exploratory research project consists of four major components: 1) a density functional theory for the microscopic structures of colloidal dispersions; 2) calculating pair and multibody colloidal forces and colloidal structure with an emphasis on those containing multivalent salt ions and polymers; 3) calculating colloidal phase behavior including structural ordering and metastable fluid-fluid equilibrium; 4) Experiments on poly-N-isopropylacrylamide (PNIPAM) dispersions for the calibration of calculated results. Thermally responsive PNIPAM dispersion is selected in this exploratory research because the physiochemical properties of the particles and the colloidal forces can be easily controlled by tuning the preparation conditions and the composition of the aqueous solution. The colloidal phase diagrams, structure factors, ionic distributions, osmotic second virial coefficients, and particle size distributions of charged as well as polymer-containing PNIPAM dispersions will be studied using small-angle neutron scattering (SANS) and conventional static and dynamic light scattering (SLS and DLS) measurements.Intellectual MeritsThis exploratory research holds significant intellectual merits for its synergetic combination of novel theoretical approaches with SANS to represent the interfacial structural and thermodynamic properties of complex systems. The molecular models developed in this work will be useful, among numerous other applications of soft condensed matter, for developing theoretical guidelines in the selection of solution conditions during the fabrication of a new generation of nanostructured materials using submicron building blocks.Broader ImpactsThis SGER research project can lead to a number of broad impacts. First, results from this work will provide the essential basis for new courses on theory and experiment of colloidal self-assembly that will be of interest to both undergraduate and graduate students working in related fields. Students trained in this area will be highly marketable and will be able to pursue highly productive careers in nanotechnology. Second, this work will provide support for socioeconomically disadvantaged students from the University of California at Riverside to participate in research and gain interdisciplinary skills in theoretical modeling and cutting edge experimental techniques such as neutron scattering. Finally, the publications resulting from this exploratory work will have significant impacts on both fundamental research and technological applications related to materials at the interface.