Title

A mechanistic investigation of the preparation of a polymer-ceramic nanocomposite: Polyimide/aluminum nitride

Date of Completion

January 1996

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

The objective of this dissertation is to synthesize a novel class of advanced polymer-ceramic nanocomposites, namely polyimide (PI)/aluminum nitride (AlN) nanocomposites, and to investigate their unique properties. Such nanocomposites have been initially proposed for improving the thermal and mechanical properties of polymers, as well as for increasing the packing density of nanosized fillers with a uniform dispersion. The fundamental aspect of this study involved a probing of interactions at the solid-liquid interface during the mixing of the organic and inorganic phases, and the property-structure dependence of the materials. The systematic approaches for the study on the polymer-ceramic nanocomposites included: (i) synthesis and characterization of the nanostructured ceramic nitrides; (ii) preparation of a series of compositions of the PI/AlN nanocomposites; (iii) investigation of the surface chemical structures of the AlN nanopowder, which is related to the nature of the agglomerated structure and the physical-chemical interactions in the solid-liquid suspension; (iv) study and development of strategies for the deagglomeration and stabilization of nanostructured AlN particles in multi-component nonaqueous systems; and (v) evaluation of the polymer/ceramic nanocomposites for enhanced properties, i.e., coefficients of thermal expansion, thermal conductivity, and mechanical properties.^ An effective sol-gel type of chemical synthesis route has been developed for the synthesis of nanostructured ceramic nitrides, which involved aqueous reaction media and moderate preparation conditions. Furthermore, PI/AlN nanocomposItes with a very high packing density (65 vol.%) were obtained through an efficient suspension mixing method. The homogeneous composites showed a trend of increasing thermal conductivity, decreasing thermal expansion, and increasing hardness and Young's modulus, as the ceramic loading increased. A detailed mechanistic investigation of the preparation process, via in-situ FT-IR analysis of a series of probe molecule reactions on the particle surface, along with rheological characterization, suggested that (i) chemisorption plays an important role in the mixing of a nanoparticle/organic dispersion; and (ii) surface acid-base reaction and proton transference are the most efficient interactions during the suspension processing for the chemically synthesized nanostructured AlN powders. ^