Browsing by Author "Roberts, M. W."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Adsorption of neopentane on tungsten and palladium films
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Ross, J. R. H.; Roberts, M. W.; Kemball, C.
    The adsorption of neopentane has been studied on tungsten and on palladium films; allied experiments were carried out with methane (W, Pd) and with propane (W). The evolution of hydrogen from each gas/metal system was studied as a function of time and temperature; reaction with gas phase deuterium was used to determine how many of the hydrogen atoms in the surface phase were exchangeable, either rapidly or by slower processes. Rapid dissociative chemisorption, involving the cleavage of an average of 3 or 4 C—H bonds occurred with neopentane or propane on tungsten. Neopentane was chemisorbed on palladium at room temperature but dissociation of methane was not observed below ∼373 K; the extent of the dissociation of both hydrocarbons was smaller than on tungsten. Further breakdown of the surface species, accompanied by evolution of hydrogen, occurred with all systems on raising the temperature. Evidence for C—C bond rupture was obtained from the hydrogenolysis of neopentane at higher temperatures.
  • No Thumbnail Available
    Item
    Contact Angle Studies of Some Low Energy Polymer Surfaces
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Murphy, W. J.; Roberts, M. W.; Ross, J. R. H.
    We have explored the possibility of acquiring information on the molecular nature of some novel polymer films by following Zisman’s approach of determining the critical surface tension yc which is considered to reflect the molecular composition of the solid surface. This led us to obtain equilibrium contact angle data, using both a series of pure liquids and various alcohol solutions, not only with the polymer films but also with solid surfaces of polystyrene and polymethylmethacrylate. Lower values of yc were obtained with the solutions than with the pure liquids; these lower values are attributed to the preferential adsorption of the alcohol molecules at both the polymerliquid and the polymer-vapour interfaces. The value of yc depends on the alcohol used, and is relatively independent of the solid : it is inferred that the alcohol is adsorbed with the hydroxyl group towards the polymer surface. It is concluded that in certain cases, the value ofyc obtained using solutions cannot be used as being characteristic of the solid (as has been suggested by Zisman), and that changes at the solidvapour interface cannot be neglected when interpreting contact angle data. Several sets of data reported in the literature are discussed from this viewpoint. The Gibbs adsorption isotherm is applied to the contact angle data and the results add further weight to the conclusions regarding the occurrence of adsorption at both interfaces.