One particularly promising model of electrical properties of conductive nanocomposites involves a combined quantum tunneling/percolation approach. However, two key inputs to the model-the polymer matrix barrier height and the average gap between conductive filler particles-are difficult to determine experimentally. This article demonstrates improved methods for determining barrier height in polymer materials via conductive nanoindentation, with barrier heights measured between 0.4 and 1.7 eV for five different polymers. By using dielectric spectroscopy techniques, combined with the barrier height measurements, the average junction gap was determined for the first time for nickel-nanostrand nanocomposites with six different polymer matrices; the values range from 1.31 to 3.28 nm. Using those measured values for barrier height and junction gap distances in a simple model, we have tested predictions for bulk resistivity of six polymers. The model worked well for four of the six, which suggests that for a given volume fraction of filler, knowledge of the barrier height and the junction distance may in many cases be sufficient to provide an estimate of the bulk resistivity of the polymer-nanostrand blend, an important parameter in nanocomposite engineering.
Electromagnetic interference (EMI) and electrostatic discharge (ESD) shielding effectiveness of M55/RS-3 composite (i.e., carbon fiber in a toughened polycyanate resin matrix) combined with nickel nanostrands TM was investigated when subjected to the monotonic tensile load. These were quantified in the terms of dB attenuation and sheet resistance, respectively. A baseline panel without nanostrands TM and three lay-ups with different locations of nickel nanostrands TM layers were characterized. These locations were outside surfaces, dispersed throughout the laminate thickness or the mid-plane. The nanostrands TM are capable of providing EMI and ESD shielding protection without any detrimental effects on the mechanical behavior of the composite (i.e., damage mechanisms and ultimate tensile strength) under the tensile loading condition. The placement of nanostrands TM on the exterior surfaces in the composite lay-up provided better EMI and ESD shielding effectiveness. The EMI protection capability from nanostrands TM at any location was practically constant with increasing tensile load up to the final fracture. However, sheet resistance did not change with increasing tensile load only when nanostrands TM were placed at the outside surfaces. The nanostrands TM layers were not damaged until the final composite fracture. FIG. 12. (a) Damage details of interlaminar panel near fracture region and (b) magnified view of marked area. FIG. 13. Damage details of exterior panel near fracture region.
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