Collaborative Research: New Routes for the Preparation and Characterization of Functionally-Graded and Mesoporous Silica Thin Films

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Professor Daniel A. Higgins of Kansas State University and Professor Maryanne M. Collinson of Virginia Commonwealth University are supported by the Analytical and Surface Chemistry Program to explore the synthesis and properties of novel mesoporous films. The preparation of films and surfaces incorporating compositional gradients is a topic of contemporary scientific interest. Such "functionally graded" materials incorporating gradients in polarity, porosity, and ionic site density have potential applications as stationary phases for separations, as absorbent/adsorbent layers for use in chemical or biological sensors, and as a means to regulate surface adhesion of cells, to direct the growth of neurons, and even to drive the transport of liquids. In this collaborative proposal, a unique approach is being studied for creating silica films that incorporate gradients in thickness, porosity, and composition using sol-gel chemistry and contemporary electrochemical deposition techniques. The inherent complexity and the variable nature of these materials inspired the use of single molecule imaging and spectroscopy (SMS) to obtain detailed information at the nanoscale and molecular level. SMS methods will be developed to obtain information on variations in pore size and microenvironment polarity along the gradients. In addition to these new functionally graded materials, mesoporous materials that exhibit reversible shrinkage in response to drying or changes in solution properties will also be made and characterized at the single pore level. Materials that exhibit reversible shrinking and expansion are potentially useful for the capture and sequestration of pollutants and for the controlled release of drugs, pesticides and fertilizers. Novel single-molecule fluorescence resonance energy transfer (FRET) methods will be used to monitor pore size variations in these materials with nanometer-scale sensitivity. Students participating in this research at Kansas State and Virginia Commonwealth will receive an unusually broad experience in synthesis, materials science and single molecule spectroscopy. All the participants involved in this research will benefit from the comprehensive education provided by this program via the sharing of knowledge, data and materials in weekly web conferences and periodic site visits to the collaborating laboratories.