Synthesis and Characterization of Various Inorganic Particles and Organic/Inorganic Hybrid Nanocomposites

Abstract

The field of nanocomposites involves the study of multiphase materials where at least one of the constituent phases has minimum one dimension less than 100 nm. The promise of nanocomposites lies in their multifunctionality and the possibility of realizing unique combinations of properties impossible to achieve with traditional materials. Organic/inorganic nanocomposites exhibit combination of properties of both polymer and the resultant material such as elasticity of organic materials and rigidity of inorganic materials. In this thesis, physical and chemical properties of inorganic particles (silica, imogolite, gibbsite and boehmite) are investigated considering their applications for preparation of nanocomposites. Part 1 of the thesis describes various inorganic particles such as silica, imogolite, gibbsite and boehmite. In the first section, synthesis methods of silica and imogolite are presented. Size of silica particle is controlled by adjusting amount of reagent, and synthesis process of imogolite was introduced. In the second section of part 1, thermodynamically controlled synthesis of imogolite nanotubes with different diameters is investigated. During synthesis of imogolite, the findings provided clear evidence about the role of temperature on the curvature of protoimogolite clusters and imogolite nanotubes. It is also demonstrated in the part that diameter of imogolite nanotubes depends on the degree of SiOH substitutions. Synthesis of gibbsite and boehmite from different initial nucleates of imogolite by adjusting the temperature and chemical reagent are described in the third section of the part 1. The Gibbs free energies of gibbsite and boehmite are calculated to determine the structures. At low temperature, gibbsite nucleates form a Lozenge-shaped morphology, while boehmite nucleates on the internal and external surfaces of the decomposed gibbsite particles resulting in the formation of fine crystallite clusters at high temperature. Part 2 describes the organic/inorganic nanocomposites which consisted with inorganic particle which came up in part 1 are introduced. In the first section of part 2, a new way of synthesizing hydrogels with higher mechanical strength by a silica/PAA hybrid system is reported. The physical property and chemical bonding between polymer and inorganic particle of nanocomposites are presented. Most polymer chains are chemically grafted onto the surface of silica particles. And the bonding characterization is successfully observed to check the conformational changes. In the second section of part 2, the other organic/inorganic hybrid hydrogel containing imogolite instead of silica particle is demonstrated. It shows improved elongational property. The hybrid hydrogel, a composite of imogolite as an inorganic material and acrylic acid as an organic material, shows great tensile strength up to about 1800% extension, and it recovers its original shape immediate after the release of stress. The imogolite acts as a reinforcing filler that maintains the structure, and the PAA acts as flexible chains that contribute to elongation properties. The structure of these materials conformed to simulate Raman analysis and their particle alignment under tensile stress is studied by SAXS. This work will give a new way to synthesize the polymer by γ-ray irradiation and expand research area of organic/inorganic composite material for various applications. In the third section of part 2, the γ-ray irradiation is applied to silicon wafer. An innovative method for grafting polymers onto silicon wafers is developed. The irradiated silicon wafer acts as its own initiator. The thickness of PAA on the silicon wafer by adjusting the polymerization time is controlled. Growth factors are controlled to yield thicknesses ranging from 20 nm to 3 mm and to make a pure acrylic acid gel. This study could serve as the basis for developing the simplest methodology for obtaining thin polymer films on solid substrates. Last section is about self-healing materials which prepared by γ-ray irradiation. Selfhealing materials have the ability to repair damage in the form of cracks and propagation. In this thesis, PEO films prepared by a simple γ-ray irradiation method that induced by water to self-heal at room temperature. The strategy of self-healing is using only polymer chain entanglement without any healing agent or external stimulus. Water molecules allow the PEO chains to diffuse across the fractured surface to become intermixed and entangled. Halloysite applied to PEO film as a reinforcement filler presents the effect of halloysite on mechanical properties and healing-efficiency of PEO film. It suggests a new property of PEO itself and a novel strategy for inducing self-healing property.