Applications of ESCA to polymer chemistry. XII. Structure and bonding in commercially produced fluorographites

Abstract

AbstractA series of fluorinated graphites, Fluorographites, of varying fluorine content has been examined by ESCA, and the chemical shifts and relative intensities of the core electron lines yield a consistent picture of the compositions and structures in the surface regions of the materials. Fluorographites of composition (C1F0.81)n to (C1F1.00)n are fully fluorinated in the outermost ∼40 Å and consist of a bulk structure composed of tertiary →CF groups with CF2 groups at the prismatic edges of the fluorinated graphite layers. This is also the case for (C1F1.05)n, but, in addition, some of the CC bonds involving edge →CF carbons are broken and replaced by CF bonds, giving a higher concentration of CF2 groups at the outermost surfaces of the particles of this material. The ESCA data for (C1F0.25)n are consistent with a structure comprising six‐membered aromatic rings in which each ring carbon is attached to a →CF group acting as a bridge among three similar rings, with the CF bonds alternately pointing up and down with respect to the plane defined by the carbon atoms. At the immediate surface the valence requirements of the carbon atoms at the prismatic edges of the graphite‐like layers are satisfied by bonding with oxygen. This is also the apparent structure of (C1F0.37)n, but in addition there exist discrete regions of composition (C1F1)n distributed uniformly throughout this material. The Fluorographites (C1F0.34)n, and (C1F0.40)n, and (C1F0.63)n consist of blocks of C1F1 stoichiometry and blocks of unreacted graphite. The presence of CF2 groups and the complete absence of oxygen in the surface regions of these Fluorographites suggests that the prismatic edge sites are fully fluorinated. The inhomogeneous block‐like structures of (C1F0.37)n, (C1F0.37)n, and (C1F0.34)n, (C1F0.40)n, and (C1F0.63)n, give rise to differential sample charging, resulting in apparent shifts in the binding energy scales between the spectral components originating from different regions of the samples. Such differential sample charging is also described for a number of mixtures of the Fluorographites and of graphite with the Fluorographites. It is pointed out that in view of these results it is necessary to exercise considerable caution in using the ESCA lines of an added compound as a reference in measuring core electron‐binding energies.