Molecular mechanics of binding in carbon-nanotube-polymer composites

Nanoscale composites have been a technological dream for many years. Recent ly, increased interest has arisen in using carbon nanotubes as a filler for polymer composites, owing to their very small diameters on the order of 1 nm, very high aspect ratios of 1000 or more, and exceptional strength with Young's modulus of approximately 1 TPa. A key issue for realizing these com posites is obtaining good interfacial adhesion between the phases. In this work, we used force-field based molecular mechanics calculations to determi ne binding energies and sliding frictional stresses between pristine carbon nanotubes and a range of polymer substrates, in an effort to understand th e factors governing interfacial adhesion. The particular polymers studied w ere chosen to correspond to reported composites in the literature. We also examined polymer morphologies by performing energy-minimizations in a vacuu m. Hydrogen bond interactions with the pi -bond network of pristine carbon nanotubes were found to bond most strongly to the surface, in the absence o f chemically altered nanotubes. Surprisingly, we found that binding energie s and frictional forces play only a minor role in determining the strength of the interface, but that helical polymer conformations are essential.