Fluorination of carbon blacks: an X-ray photoelectron spectroscopy study IV. Reactivity of different carbon blacks in CF4 radiofrequency plasma

The effect of CF4-plasma enhanced fluorination on the surface modification of carbon blacks has been examined using XPS. Three different types of carb on blacks have been studied: a thermal black, a furnace black and a high el ectrical conducting black. The analysis of the XPS spectra of fluorinated c arbon black samples indicates that all fluorine atoms, fixed at the surface and in a subsuperficial zone of the particles, are covalently linked to ca rbon atoms. The influence of the physicochemical properties and morphology of these three types of carbon blacks on the fluorination reaction has also been investigated. The proportion of different types of fluorinated carbon atoms, i.e. on one hand CFx surface and border groups of graphitic bulk do mains for which the planar configuration of the graphene layers is preserve d together with the sp(2) character of C, i.e. structures of type I, on the other hand polyalicyclic perfluorinated structures in which sp(3)C form pu ckered layers similar to those of covalent fluorographites, i.e. structures of type II, and also the F/C ratio of the fluorinated groups are related t o the surface morphology and depend on the microstructural organization of particles. When the microstructure ordering and graphitic character of the carbon increase, the size of the ordered graphitic domain also increases. A t the same time the density, the size of defects and proportion of protonat ed sp(3)C entities bridging the graphene layers decrease. As a consequence, the proportion of carbon atoms, potentially able to form perfluorinated CF 2 and CF3 groups, decreases. The relative contribution of those groups is a ppreciably higher in fluorinated compounds which are derived from carbon bl acks with a lower structural order. (C) 1999 Elsevier Science Ltd. All righ ts reserved.