Analysis of the surface structure of cellulose fibers using atomic force microscopy and small-angle X-ray scattering

The surface images of softwood pulp fibers were investigated with an atomic force microscope (AFM). Microfibril-like structures were observed on the fibers. Periodic domains were observed on the fibrils, and they lay in a row at every 70 nm. The surface structures were discussed in terms of the autocorrelation function calculated from the AFM images. The correlation length, ξ, obtained from the function was 70nm. This value corresponds to that directly confirmed in the original AFM images. The autocorrelation function can be converted into the power spectral density (PSD). The PSD decayed versus the absolute value of wave number vector, k, according to a power-law. The exponent value was-2, which indicates that no fractal structures exist on the fiber surface. The other power-law decay was observed for the small-angle x-ray scattering (SAXS) intensity of the fiber. The intensity followed Porod's inverse fourth power law. These two results indicate that the surface structure of the fiber is definitely bordered. The coincidence of the two different analyses implies that the PSD obtained from the AFM images can be interpreted as a scattering image of surface under the ambient condition.