Manufacture of colloidal polymer ellipsoids for anisotropic conducting nano-composites

Abstract

This project aimed to make anisotropic conducting nano-composites based on a segregated system of 20 nm gold particles and deformed polyethylene spheres of colloidal size. Two methods for achieving the deformation of the colloidal polyethylene spheres were attempted, namely to exploit the elongational flow field at the entrance to a capillary and alternatively to make cast films of a water soluble polymer containing the colloidal particles and draw them in the solid state. In the latter method, sections of film were elongated at an elevated temperature using a tensile testing machine. The drawn films were dissolved in water and the deformed particles were extracted and concentrated by ultracentrifugation. This method was successful in producing ellipsoids of a prescribed aspect ratio. Further successful deformation was carried out using PMMA particles and monodisperse polystyrene particles. Polystyrene spheres containing 20 nm diameter magnetite particles could not be deformed using this process. A range of experimental techniques were exploited to characterise the ellipsoidal particles, including transmission electron microscopy and photocorrelation spectroscopy. Subsequent addition of metal oxide particles to the polymer ellipsoids resulted in some success in that a small number of 20 nm diameter magnetite particles was observed to be attached to the surfaces of the much larger (1 μm) polystyrene ellipsoids. The mechanism of attachment has not yet been elucidated but this has significant potential for future composite device production.