N-Type Thermoelectric Performance of Functionalized Carbon Nanotube-Filled Polymer Composites
Carbon nanotubes were dispersed and functionalized with polyethylene imine (PEI) before incorporation in a polyvinyl acetate matrix. The resulting samples exhibit air-stable N-type characteristics with electrical conductivities as great as 1600 S/m and thermopowers as high as 100 microV/K. Thermopowers and electrical conductivities correlate, in a reversal of the trend found in typical materials. This phenomenon is believed to be due to the increase in the number of tubes that are evenly coated in a better dispersed sample. Increasing the amount of PEI relative to the other constituents positively affects thermopower but not conductivity. Air exposure reduces both thermopower and conductivity, but a stable value is reached within seven days following film fabrication. The atmospheric effects on the electrical conductivity prove to be reversible. Oxygen is believed to be the primary contributor to the decay.