A study of carbon black Corax N330 with small-angle scattering of neutrons and X-rays

Carbon black Corax N330 (hereinafter called CB) is used as a filler in elastomers. The properties of the surface are important for the binding of the elastomer to the carbon black particles. Porod's law requires the intensity to satisfy I(q) approximately q(-alpha) with alpha = 4 for large q. Rieker et al. observed alpha = 3.7 +/- 0.1 for small-angle X-ray scattering (SAXS) data and concluded that the particle surface is fractally rough. Ruland critized this and suggested that the observed deviation is due to fluctuations of the spacing of the graphitic layer planes ("graphenes") which contribute a component I(q)fluc = 1Cflucq(-2) to the intensity component satisfying Porod's law. We studied CB by nitrogen adsorption, high-resolution transmission electron microscopy, synchroton SAXS, and small-angle neutron scattering (SANS). Our SAXS experiments with samples of high transmission (Tr = 0.96) confirmed the form of the scattering curves published by Rieker et al., but the correction for I(q)fluc restored Porod's law. SANS experiments were performed with a sample of low transmission in order to analyze the high q-range for scattering from voids and isolated graphenes. We found I(q) approximately q(-beta) with beta approximately 2 at q > 2.5 nm(-1) and will show that this intensity component requires graphenes consisting of about 12 benzene rings. The contrast matching technique revealed the presence of inaccessible voids. The SANS data for a sample with Tr = 0.363 satisfy Porods law, in contrast to the SAXS data for the high transmission samples. The latter discrepancy is likely due to the lower resolution of the SANS measurements because of wavelength smearing and multiple scattering. A SANS sample with Tr = 0.97 shows a minor deviation from Porod's law only (alpha = 3.9). The original SANS data and the SAXS data corrected for the fluctuation component indicate that the CB surface is essentially smooth.