Surface and bulk characterisation of selected coals, bitumens and polymers as revealed by esca and other analytical techniques

Abstract

Electron spectroscopy for chemical applications (ESCA) has been used to study aspects of the surface chemistry of some polymeric materials of well defined composition, and in the characterisation of some naturally occurring carbonaceous materials, with particular attention to coal. The selective surface modification of polymers by means of both straight hydrogen and oxygen plasmas and sequential plasma treatments has been studied. A detailed account of the changes in functional group distribution upon treatment is presented. The surface treatment of polyvinyl alcohol with trifluoroacetic anhydride has been monitored using the non-destructive depth profiling capabilities of ESCA. Experimental results are complemented by data from computer simulation. The trifluoroacetylation of the surface hydroxyl functionalities of cellulose has been investigated. Aspects of the preparation and surface chemistry of polyacetylene have been explored, with special reference to its passification towards atmospheric oxidation. The application of a mild hydrogen plasma treatment, prior to air contact, was found to produce an essentially hydrocarbon-like overlayer, more resistant to atmospheric oxidation than the untreated polyacetylene. Oxidation of the material beneath the overlayer did occur, possibly due to poor oxygen barrier properties of the overlayer. A critical account of the use of ESCA in the understanding of the structure, bonding and reactivity of coal and coal-related materials has been presented. The value of ESCA in the characterisation of surface specific reactions has been exemplified by studies of surface oxidation reactions, both naturally occurring through weathering processes, and artificially induced via irradiation with ultra-violet light. Other analytical techniques, including optical microscopy, solid state nuclear magnetic resonance and incoherent inelastic neutron scattering spectroscopies have been employed and provide supplementary data.