Synthesis and Applications of Inorganic/Organic-Polymer Nanocomposites
Ajayan, Pulickel M.
Doctor of Philosophy
This research work focuses on developing new synthesis routes to fabricate polymer nanocomposites tailored towards different applications. A simple, one-step method has been devised for synthesizing free-standing, flexible metal nanoparticlepolydimethylsiloxane films. This process simplifies prevalent methods to synthesize nanocomposites, in that here nanoparticles are created in situ while curing the polymer. This route circumvents the need for pre-synthesized nanoparticles, external reducing agents and stabilizers, thereby significantly reducing processing time and cost. The resulting nanocomposite also demonstrates enhancement in mechanical and antibacterial properties, with other envisaged applications in biomedical devices and catalysis. Applying the same mechanism as that used for the formation of bulk metalsiloxane nanocomposites, metal core-siloxane shell nanoparticles and siloxane nanowires were synthesized, with octadecylsilane as the precursor and in situ formed metal nanoparticles (gold, silver) as the catalyst. This method offers some unique advantages over the previously existing methods. This is a room temperature route which does not require high temperature refluxing or the use of pre-synthesized nanoparticles. Furthermore, this synthesis process gives a control over the shape of resulting nanocomposite structures (1-D wires or 0-D spherical particles). High thermal stability of polydimethylsiloxane (PDMS) makes it viable to alternatively synthesize metal nanoparticles in the polymer matrix by thermal decomposition process. This technique is generic across a range of metals (palladium, iron, nickel) and results in nanoparticles with a very narrow size distribution. Membranes 111 with palladium nanopartic1es demonstrate catalytic activity in ethylene hydrogenation reaction. Additionally, a new nanocomposite electrode has been developed for flexible and light-weight Li-ion batteries. Flexible films were prepared by the integration of the poly(vinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer electrolyte with the three-dimensional (3D), nanostructured electrode composed of aligned carbon nanotube (CNT)-copper oxide hybrid. This hybrid electrode was fabricated by a combination of chemical vapor deposition and electrodeposition techniques. Embedding it in PVDF polymer results in a flexible system and also renders an external separator redundant. This new design shows an improvement in electrochemical performance over pure CNTs as both CNTs and CU20 contribute towards electrochemical activity. Efforts have also been undertaken towards synthesizing synthetic adhesives by mimicking the design principles found in nature. Aligned patterned CNTs have been used to replicate the fibrillar structure found in geckos' toes which generates adhesion through van der Waals forces. The adhesive forces in CNTs were found to be higher than in geckos and the key to this phenomenon lies in the extensive side-wall contact obtained on compressing CNTs against a surface.
Applied Mathematics; Mechanical engineering; Materials science