ChemE Colloquia- KAREN WINEY, University of Pennsylvania
Electrical Properties in Polymer NanocompositesKaren I. Winey Department of Materials Science and Engineering
University of Pennsylvania
Nanoparticles, particularly carbon nanotubes and metal nanowires, provide new routes for engineering the electrical properties of polymers. This lecture will focus on two aspects of this expanding field, namely electrical conductivity and resistive switching. With regard to electrical conductivity, Wineys group has demonstrated the importance of nanotube orientation both via simulation and by melt processing the nanocomposite to align carbon nanotubes and using X-ray scattering to quantify the extent of orientation. To better compare simulations and experimental results, Wineys group has made silver nanowires of well-defined aspect ratios (L/D < 50) and the experimental thresholds for electrical percolation compare favorably with both their simulations and analytical models as a function of aspect ratio. Most recently, Wineys group has extended the simulations to polydisperse systems and thin films. The study of electrical percolation in polymer nanocomposites presumes that two states dominate such that below and above the critical concentration the electrical conductivity is dominated by the insulating matrix and by the conductive fillers, respectively. In contrast, Winey and her group have found resistive switching in nanocomposites of silver nanowires and polystyrene, wherein these bulk materials can reversibly transform from high to low resistance as a function of applied voltage. Cyclic voltammetry measurements at 10K are consistent with the hypothesis that applied voltage can form conductive silver filaments between neighboring nanowires. Dynamic electrical properties in bulk polymer nanocomposites may enable new applications for polymer nanocomposites as functional materials.
Reception at 3:30 PM in 801 Mudd.