Effect of the oxygen plasma treatment parameters on the carbon nanotubes surface properties

The physical and mechanical properties of fibres/polymer composites depend primarily on the properties of the combined materials, the surface of the fibres, the interface between the two components as well as the mode of stress transfer at the interface. Establishing appropriate fibre/matrix adhesion is the key to imparting good mechanical properties to a fibre-reinforced polymer matrix composite. Modem theory explains adhesion behaviour in terms of a microscopic layer existing at the interface with different properties from those of either the fibre or the matrix. In order to optimise the fibre/matrix interactions, it is often essential to functionalise the fibre surface. One possible way is the plasma treatment of the fibres, a process which will not significantly diminish the fibre strength. Vapour grown carbon nanotubes (VGCNT) were treated in an oxygen plasma. The effects of plasma power, chamber pressure, plasma frequency (radio frequency-RF or microwave-MW) as well as the effects of the treatment time on the quantity of functional groups (carboxylic, carbonilic, hydroxylic, phenolic) introduced onto the fibres surface were examined. Contact angle and surface energy measurements, XPS-Analysis, titration with NaOH showed a better wettability (at least 60% more) of the VGCNF treated by MW-plasma. The lower the contact angle is, the better the liquid will wet the solid. Direct measurement of the surface energy of a solid is difficult to carry out and is generally obtained by determining the wetting behaviour of liquids of known surface energy. In many cases the consideration of dispersive and polar interactions is sufficient for carbons and polymers. It is noticed that the polar component increases and in some cases becomes the major factor contributing to the surface energy of the carbon fibre. Nevertheless, wetting is an important factor for the achievement of an adequate impregnation of the fibres by the liquid polymers during manufacturing of the composite. (c) 2005 Elsevier B.V. All rights reserved.