Surface-induced polymer crystallization in high volume fraction aligned carbon nanotube-polymer composites

Surface-induced crystallization of high-density polyethylene in vertically aligned multiwalled carbon nanotube arrays has been investigated by means of scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). 1-mm long nanotube arrays are infiltrated by polyethylene solutions and then the system is allowed to crystallize under controlled conditions. Periodic disk-shaped polyethylene single crystals grow perpendicularly to the aligned nanotubes but do not completely fill the intertube spacing, forming oriented 3D porous structures. This unique morphology leads to low density, high nanotube mass fraction (up to 80wt.-%) composites. Microstructure (WAXD) analysis shows that the nanotubes act as both orientation templates as well as nucleating agents for polyethylene crystallization creating orthorhombic and mono- clinic forms, although the overall crystal structure is dominated by the orthorhombic form. Thermal analysis (DSC) shows that the nanocomposite exhibits multiple phase transitions during heating and cooling with a weak superheating and supercooling dependence on different scanning rates. Three phase structures have been identified and a possible model is proposed to explain the observed phenomenon. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.