표면 개질에 의한 실리카의 분산성 향상 및 폴리아미드이미드와의 복합체에 대한 응용

Abstract

Nano sized silica nanoparticles have been widely used in many applications such as catalyst, film substrate, insulator, adsorbent, nano-composite, energy storage materials, etc. The sol-gel method has been successfully used for the fabrication of many inorganic particles since Stober method in 1968. Monodispersed silica nanoparticles were synthesized from aqueous solutions of silicon alkoxides containing ammonia. And additionally the introduction of functional group was needed on the surface of silica nanoparitlces for useful properties because many application require specific surface properties. The surface modified silica nanoparticles were prepared through two-step sol-gel process. The introduction of functional group onto the surface of silica nanoparticles could be processed by varying the amount of silane coupling agent, pH and R (molar ratio of H2O/Si) during the surface modification step. The silane coupling agent containing the phenyl group was used to modify the silica nanoparticles for blocking the agglomeration which caused from restrictions on the utilization. The qualitative analysis of modified silica nanoparticles was conducted with Fourier transform infrared spectroscopy (FT-IR) and 29Si solid state nuclear magnetic resonance (NMR). The degree of surface modification at the silica nanoparticles was examined based on the surface hydrophilic/hydrophobic moiety, surface charge and morphology. Thus our research primarily aims the mechanism of surface modification depend on the experimental condition. Under fast hydrolysis and condensation conditions, the silane coupling agent is clustered on the surface of silica nanoparticles and, on the other hand, it is homogeneously present on the surface of silica nanoparticles in monomeric form under slow conditions. The silica is a need for a composite with PAI, which is required the more severe condition in the industry. When the silica nanoparticles were dispersed in N- methyl-2-pyrrolidone (NMP) as organic solvent, the surface modified silica nanoparticles were better in dispersion stability at high concentration (20%) caused by the influence of phenyl group, resulting in the well dispersed in further polymer matrix such as polyamide-imide(PAI) under the presence of an additional amino group. The modified silica/PAI nanocomposite film showed no significant agglomeration by cross-sectional field emission scanning electron microscope (FE-SEM) image. The thermal stability and mechanical properties of the modified silica/PAI nanocomposite films have been improved. Especially tensile strength at yield point of nanocomposite films using 6 % modified silica nanoparticles with respect to PAI showed a significant increase by 30.58 % and the elongation at break point of nanocomposite films using 3 % modified silica nanoparticles with respect to PAI was improved by 12.46 %. Although the silica nanoparticles have a high surface energy and hydrophilic surface, it has a good compatibility with polymer due to specific surface modification.