Synthesis and Characterization of Sol-Gel Nanocomposites Demonstrating Enhanced Mechancial Properties

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Title: Synthesis and Characterization of Sol-Gel Nanocomposites Demonstrating Enhanced Mechancial Properties
Author: Mosher, Brian Patrick
Advisors: Fuh-Gwo Yuan, Committee Member
Angus Kingon, Committee Member
Taofang Zeng, Committee Chair
William Roberts, Committee Co-Chair
Abstract: The mild reaction conditions of the sol-gel process allow incorporation of an inorganic component into organic materials, making it very favorable for the synthesis of organicinorganic nanocomposite materials. However, researchers still strive to produce materials with the unique properties of inorganic compounds which also possess the mechanical properties of organic polymers. We have developed several sol-gel derived nanocomposite silicate materials using both inorganic precursors and organic-inorganic precursors, which show superior mechanical properties due to nanoscale structural reinforcement. The materials reported were developed in three separate investigations, although the synthesis techniques are relatively similar. STRUCTURAL EVOLUTION OF PARTICLE REINFORCED ORGANIC-INORGANIC WATER-BASED NANOCOMPOSITE MATERIALS We present for the first time, the use of Al(ClO4)3, an effective catalyst for synthesis of 3-Glycidoxypropyltrimethoxysilane (GPTMS) - based nanocomposite materials via sol-gel chemistry. Aluminum perchlorate (Al(ClO4)3) simultaneously serves as catalyst for epoxy polymerization and methoxysilane hydrolysis at room temperature. Catalytic effects of Al(ClO4)3 were demonstrated through nuclear magnetic resonance (NMR) of precursor sols and structural investigation of resulting films by Fourier transform infrared spectroscopy (FTIR). Our method incorporates nanophase particulate reinforcement; Ludox® TMA colloidal silica, which possesses surface silanols (Si-OH), further activate the epoxy groups and expedite organic polymerization. The silica nanoparticles chemically link with the organic-inorganic network through Si-O-Si and Si-O-C bonds. Nanoparticles reinforcement serves to strengthen the network and enhance mechanical properties such as microhardness and abrasion resistance while maintaining the unique optical properties of these materials. Furthermore, the synthesis is water-based, providing for an environmentally friendly synthetic route to hybrid materials. We present a general strategy for synthesis of particle reinforced nanocomposite organic-inorganic sol-gels that can serve as a building block for synthesis of more advanced hybrid materials. PARTICLE-REINFORCED WATER-BASED ORGANIC-INORGANIC NANCOMPOSITE COATINGS FOR TAILORED APPLCATIONS Based on the concepts in the work described above, we further developed synthetic routes to three organic-inorganic coatings with nanoparticle reinforcement, which serves to enhance mechanical properties. The films are sol-gel derived using non-ionic surfactant, with aluminum perchlorate (Al(ClO4)3) as a catalyst and 3-Glycidoxypropyltrimethoxysilane (GPTMS) as precursor. Through the aid of nanoparticle colloids and a minute amount of catalyst, dense, hard and monolithic materials are obtained. Incorporating metal oxide nanoparticles brings forth unique properties, such as absorbing harmful UV radiation. Silica colloid composites provide greatly enhanced mechanical properties without modifying the unique optical properties of inorganic materials. Water-based synthesis of these coatings is straightforward and produces very few harmful byproducts, making them ideal materials in industry. The materials presented are relatively hard and abrasion resistant with very good adhesion; two of the coatings are UV absorbent. Various colloids can be employed in our methods to tailor properties and resulting materials may serve applications such as optical, protective, catalytic, guest-host, and multifunctional coatings. ENHANCING MECHANICAL PROPRETIES OF SILICA AEROGELS THROUGH NANOENGINEERING Furthermore, we have developed a novel method to prepare modified silica aerogels, in which a small amount of water-soluble inorganic synthetic nanocomposite is added (Laponite® RDS). The molecular-level synergism between silica nanoparticles and molecular cross-linkers inverts the relative host-guest roles in glass-polymer composites, leading to new stronger and more robust low-density materials. After drying with supercritical CO2, the materials were characterized by 3-point bending, transient hotwire techniques, bulk density measurements, transmission electron microscopy (TEM), and Brunauer, Emmett and Teller (BET) method. Transient hotwire methods confirm that the nanocomposite materials retain the ultra low thermal conductivity of pure silica aerogels.
Date: 2007-10-13
Degree: MS
Discipline: Mechanical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/685


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