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Sol-gels and self -assembly: Approaches to structured materials

Trent Heinz Galow, University of Massachusetts - Amherst

Abstract

The sol-gel process is a convenient technique to prepare silicate materials with a variety of functions. These functional materials are formed via a ‘top-down’ fabrication process in which dopants are added at the commencement of the sol-gel process. However, despite the incredible versatility of these systems, issues remain regarding the mechanism of covalent entrapment of dopants. Therefore, we demonstrated how Flavin Mononucleotide acted as a dynamic conformational probe to study the covalent cross-linking of dopants into silica. It was shown that covalent entrapment occurs early in the sol, contrary to that observed for unbound probes. ^ Self-assembly is prevalent in nature and is responsible for a vast array of highly ordered architectures observed in living organisms. It is only recently, however, that self-assembly has become an important tool for ‘bottom-up’ fabrication of complex multi-scale macroscopic composites. Attachment of recognition units onto nanoparticles and polymers provides a modular approach to precisely programmed assemblies in a relatively rapid fashion. Even though the macrosystems may be mechanically robust, they are able to retain the reversible and dynamic attributes of self-assembly. ^ We exploited self-assembly to create ‘building-block’ and ‘bricks and mortar’ approaches to highly reactive, recyclable heterogeneous catalysts. By attaching complementary amines and carboxylic acids onto nanoparticles and polymers and mixing at different ratios, aggregates with distinct architectures were observed driven by electrostatics. Active catalysts were prepared by calcination, and the investigations showed substantial improvements in catalytic performance compared to their commercial counterparts were observed for hydrogenation and Heck reactions. ^ A further application of controlled assembly was established when we encapsulated a recognition-derived guest into the polar pocket of folded ‘micellar’ polymer. Diaminotriazine-functionalized polymer folds into unimolecular ‘micelles’, in which the diaminotriazine units are inwardly directed to form polar pockets providing a complementary environment to the guest. Encapsulation was verified by NMR and cyclic voltammetry studies. ^ Finally, self-assembly was adapted to polymer systems. Polymers comprised of complementary recognition units formed giant vesicles through specific interchain hydrogen bonding. It was also shown that recognition-derived nanoparticles could be specifically incorporated into the walls, providing a potential route to new templated nanocomposite macrosytems. ^

Subject Area

Chemistry, Organic

Recommended Citation

Trent Heinz Galow, "Sol-gels and self -assembly: Approaches to structured materials" (January 1, 2001). Doctoral Dissertations Available from Proquest. Paper AAI3027201.
http://scholarworks.umass.edu/dissertations/AAI3027201

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