Conductive filler/polymer composite foams (CPC) with micro-/nano-scale bubbles have attracted much attention due to their various advantages. Understanding the evolution of electrical behavior in CPC foams is important for their functional application. This thesis investigated the foaming effects on the re-alignment of the conductive filler and the subsequent conductivity percolation threshold of CPC foams experimentally and theoretically. The polystyrene (PS) and multiwalled carbon nanotubes (MWCNTs) were selected as the model system for analysis. In the experimental approach, we prepared a series of PS/MWCNTs composite foams using solvent-mixing method to blend PS and MWCNTs followed by the conventional batch foaming. It was found that at a relatively low void fraction, the electrical conductivity can be increased, and the percolation threshold can be decreased. In the theoretical modeling, a novel resistive network model based on Monte Carlo simulation to directly predict the electrical conductivity of CPC foams was developed. The model predictions agreed very well with the experimental data for both the solid and foamed composites. At relatively low void fractions (up to ~30 %), the growth of bubbles with size comparable to the MWCNT length increased the conductivity.

The methods and models developed in this work are useful tools for understanding the underlying mechanism of percolation behavior in CPC foams, as well as quantitative tools in the design of CPC foams. Furthermore, the approaches and strategies used to develop such computational model can provide guidelines and useful references for model simulation in other functional polymer composite foams, such as thermally conductive polymer composite foams.