Applications of light and X-ray scattering to characterize the fractal properties of soil organic matter

• Published in: Geoderma 1999-03, Vol.88 (3), p.251-264
• Main Authors: Rice, James A., Tombácz, E., Malekani, Kalumbu
• Format: Article
• Language: English
• Subjects: dynamic light scattering; fractal; fulvic acid; humic acid; humin; small-angle X-ray scattering; soil organic matter; static light scattering
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/S0016-7061(98)00108-6

Soil organic matter (SOM) is a heterogeneous assemblage of organic molecules that interact in a variety of ways with each other, with soil mineral surfaces, and with soil mineral colloids. Because of SOM's heterogeneity it is very difficult to define its surface, or the surfaces of the composite materials produced by its interaction with soil minerals. Yet it is at these interfaces where chemical reactions that involve SOM take place. Results are presented which describe the fractal characterization of humic materials using static X-ray and light scattering, and dynamic light scattering (DLS) experiments. The applicability of static X-ray scattering to the direct determination of the fractal dimension of humic materials is established using DLS. Over the length scales studied, humic materials are surface fractals in the solid state, and mass fractals in solution. The longer characterization length scales possible in the static light scattering experiments suggest that at longer characterization length scales humic acid is not fractal, at least not under the solution conditions employed in these experiments. Application of fractal analysis to the characterization of the surface morphology of soil and peat humin samples, the calculation of the hydrodynamic radius of humic acid particles, and the study of humic acid aggregation are discussed.