Chemically modified and doped carbon nanotube-based nanocomposites with tunable thermal conductivity gradient

Nitrogen (N)-doped and un-doped MWCNTs grown using a chemical vapor deposition (CVD) process were studied for their surface chemical modification and thermal characteristics. Various surface functional groups developed through acid purification or controlled plasma oxidation of MWCNTs were analyzed using X-ray photoelectron spectroscopy (XPS). High resolution electron microscopy was used to understand the structure and morphology of the surface-modified/unmodified MWCNTs. Thermal conductivities of surface-modified/unmodified MWCNT films were estimated using the shifts in Raman peaks for MWCNTs as a function of incident laser power (1–50 mW) and film temperature (60–160 °C). The thermal conductivity of pristine un-doped MWCNT films was much higher (∼70 W/m-K) than that of N-doped MWCNT films (∼16–27 W/m-K). Plasma oxidation or acid treatment further reduced the thermal conductivity (∼8–14 W/m-K). Thermal maps or temperature distribution profiles for MWCNT films were theoretically evaluated. Finally, different combinations of doped/un-doped and plasma/acid-treated MWCNTs were stacked and impregnated within a polystyrene matrix to result in a gradient of thermal conductivity across the thickness direction of the nanocomposite.