Solid-state NMR studies of surface chemistries in fiberglass and DNA microarray technologies.

摘要

Solid-State NMR is typically used to study the bulk properties of a sample; however, one may use solid-state NMR to study surface chemistry if careful precautions are taken to obtain satisfactory sensitivity and surface specificity. The use of probe molecules and/or surface sensitive NMR experiments enable the isolation of surface effects from those in the bulk, and, if chosen judiciously, will provide the sensitivity required for surface NMR studies.;One area of current interest, where solid-state NMR methods have been applied successfully, is the determination of surface hydroxyl concentrations of glass fibers. The hydroxyl species at surfaces of these materials are a controlling factor for their interfacial chemistry with coatings, and hydroxyl units also play a central role in adsorption, wetting, and polymer adhesion. Fluorinated silane probe molecules are an excellent means of monitoring the concentration of surface hydroxyls in low surface area glass fibers with NMR.;Using this method, practical quantification appears to be attainable at accessible hydroxyl concentrations on the order of 0.5--1.5 OH/nm 2 from samples with measured surface areas of 0.2 m2/g or higher, and these results obtained fall well within the accepted range of hydroxyl coverage for silica and multicomponent glasses. This method offers not only concentration, but also local environment information resulting from changes in the chemical shifts corresponding to silane molecules in confined environments. These applications to the characterization of the shallow microporosity/nanoroughness associated with hydroxyls at glass fiber surfaces are directly relevant to understanding fiber adsorptivity, strength, and adhesion to polymers.;A suite of calcium aluminoborosilicate fibers have demonstrated the utility of this technique in relating the effect of the total boron concentration and the connectivities of the boron species in the glass fibers to the surface morphology and hydroxyl coverage of the fiber samples. The measured hydroxyl coverages were in the range of 0.50--1.44 OH/nm2, and it was determined that as the coordination fraction of four-coordinate boron increased the hydroxyl coverage also increased. An increase in the overall concentration of boron in the glass fibers led to a corresponding increase in the microporosity of the fiber surface.;In the field of gene chip technology, understanding surface interactions between biomolecules and the accompanying solid supports is of primary importance in the development of improved techniques. Current gene chip technology utilizes amine coated glass slides for the immobilization of DNA; however, sol/gels with amine functionalization are potential high surface area substrates for gene chips. (Abstract shortened by UMI.)