Electric Field-Guided Alignment of Carbon Nanotubes in Polymer Matrix Composites for Structural Applications

Abstract

Carbon nanotubes (CNTs) have been extensively researched for diverse applications in recent years. In the present work, the use of low frequency non-uniform alternating electric fields to manipulate the alignment behavior of CNTs in an epoxy matrix has been explored for use in structural applications. CNT alignment was accomplished based on the dielectrophoresis (DEP) principle. The alignment methodology was developed and CNT alignment effectiveness was assessed through in-situ current measurements and polarized Raman spectroscopy data in addition to optical microscopy. Electrical and mechanical characterization studies were then performed on the nanocomposites containing aligned CNTs and the improvement in properties with respect to the control samples was evaluated. Further, the alignment methodology was extended to the case of hierarchical composites with geometric discontinuities. The effect of CNT orientation on the open hole tensile behavior of uni-directional glass fiber-epoxy hierarchical composites containing CNTs was evaluated as a typical case of structural loading. Different electrode configurations were employed to control CNT orientation locally around the hole with respect to the loading direction. The results indicate that altering CNT orientation locally around the hole influences the overall response of the hierarchical composite.

The thesis then discusses multiphysics simulations performed to model CNT behavior in epoxy resin considering time varying non-uniform electric fields and matrix viscosity. Considering a nanocomposite plate with a rectangular filleted notch subjected to tensile loading as a case study, numerical models were developed to enable electrode configuration design to control CNT orientation around the notch to mitigate stress concentration effects. Experimental studies were then performed with inputs from simulation studies facilitating the development of electrode set-up. The results indicate a significant enhancement in notched strength of the nanocomposite plates. Numerical and experimental studies on the development of nanocomposites containing varying concentration of aligned CNTs are also presented.