Mechanical Engineering Faculty Research

Title

Piezoresistive Behavior and Elastic Deformation of Nanoscale Graphite Platelet Reinforced Polymers

Document Type

Conference Proceeding

Publication Date

8-2005

Abstract

Polymer nanocomposites are an emerging class of multifunctional materials that have not been optimized for their functional potential. As a part of a series of studies conducted by Wong and collaborators, highly expanded graphite nanostructures were dispersed in polymers for functional property assessments. Materials processes to produce nanostructured polymer composites using the ball milling method are reported. It was found that ball milling primarily reduced particle sizes to smaller platelets. A bimodal distribution of 100 and 400 nm particles were observed using particle analyzer. This study addresses the electrical and dielectric properties of graphite platelets being dispersed in polymer matrices. The relative permittivity was found to increase dramatically with the graphite content, even at weight fraction less than 1 wt% for a wide frequency range. Piezoresistive behaviors were also studied. As applied stress increased the resistivity decreased until a critical stress was reached and, thereafter, resistivity gently increased and leveled off. The mechanisms of piezoresistivity were attributed to the formation of conductive network with graphite platelets and the collapse of conductive network at high pressure, which reduced the conductivity. Tensile and flexural tests were conducted to quantify the elastic properties arising from nanoscale reinforcements. Graphite platelets were modeled as point-like inhomogeneous inclusions. A defect Green's function was employed to simulate the elastic and dielectric properties in a unified manner. The graphite platelets were considered as disk-like inhomogeneities with a diameter of 400 nm and thickness of 100 nm. The elastic and dielectric constants were found to vary somewhat linearly with volume fraction of graphite platelets in the range studied. The modeling results were consistent with the experimentally observed data.

Publication Title

American Chemical Society Division of Polymeric Materials: Science and Engineering, 230th ACS National Fall Meeting

Volume

93

First Page

210

Last Page

212