Electric force microscopy and plasma studies of polymer surfaces

Abstract

The present work studies the functionalisation, modification and analysis of polymers surfaces for use as templates for the self assembly of nano-particles from aqueous dispersions; the production of nano-scale charge patterns; the surface autocatalytic deposition of patterned metals; and the generation of superhydrophobic, antireflective coatings. The polymer surfaces were characterised by a variety of surface sensitive techniques, such as X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Fourier Transform Infra-Red (FTIR), Electric Force Microscopy (EFM) and Video Contact Angle. The ability of an Electric Force Microscope (EFM) to create charge patterns on polymer surfaces was studied in detail. Large dc voltages were applied to a chromium coated cantilever leading to the induction of a charged region on the polymer substrate. The effects of applied voltage, tip-sample separation, scanning speed and deposition area on the resultant deposition pattern were studied. Charging thresholds for different polymer substrates were experimentally determined. A polymer blend surface consisting of nanometer sized islets of conducting polybutadiene within an insulating polystyrene matrix was also produced. The different charge storage properties of these two polymers were exploited in order to produce a nanometer scale charge patterned substrate. Charge patterns were also used as templates for the directed deposition of gold nano-particles. The pulsed plasma deposition of a 4-vinylpyridine monomer was studied in order to investigate the production of aromatic nitrogen surfaces. The retention of the nitrogen functionality allowed the plasma polymer to act as a seed site for the electroless deposition of both copper and nickel. Patterning was facilitated on a micrometer scale by embossing a grid into the polymer substrate. An investigation into the plasma fluorination of a polymethylmethacrylate yielded surfaces that combined both anti-reflective and super-repellent characteristics. The magnitudes of these properties were found to depend on the fluorine content and roughness of the treated surface.