Optimization of Electrical, Dielectric, and Electromagnetic Response in Nanocomposite Foam by Balancing Carbon Nanotube Restricted Orientation and Selective Distribution

In nanocomposite foams, one-dimensional (1D) carbon nanotubes (CNTs) with large length-to-diameter (L/D) ratios are selectively distributed in two-dimensional (2D) cell walls, featured as restricted distribution state of limiting in the cell-wall thickness direction and orienting in the cell-wall stretching direction. Such a unique CNT distribution state in nanocomposite foam significantly affects the degree of interface polarization for CNTs, conductive network construction, and electromagnetic (EM) wave interaction, hence determining the dielectric, conductive, and EM absorbing performance of the foams. Based on experiment and simulation results, the underlying synergistic interaction between CNTs and cells in nanocomposite foam is uncovered: (1) CNTs selectively distributed in polymer matrix isolated by cells (that is, the cell wall), and, hence, better dielectric, conductive, and EM absorbing performance were obtained at lower CNT volume content; (2) the 1D structure of CNTs is favorable for contacting with each other, but also leads to restricted orientation in the 2D cell walls (hence, there is an optimum CNT distribution in nanocomposite foam to optimize the corresponding performance). It was observed that larger CNT L/D ratios, easier to construct response networks, but larger CNTs restrict the degree to which the corresponding network construction is suppressed in cell walls. This optimum L/D ratio shifts to lower values as the CNT volume content in nanocomposite foam increases. Therefore, an appropriate cellular structure, CNT L/D ratio, and volume content are the prerequisites to maximize the advantages of CNT selective distribution and an easy-to-contact 1D structure, and to minimize the disadvantage of cell-wall-restricted CNT distribution, to construct optimum dielectric, conductive, and EM-absorbing networks for better corresponding performance.