Aggregation patterns and macromolecular morphology of humic substances: A fractal approach

Fractal geometry provides a powerful means for the quantitative description of heterogeneous and highly irregular systems encountered in nature. Humic substances represent a typical class of natural compounds that may be amenable to a fractal description because of their well known physical and chemical heterogeneity and molecular complexity. In this review, the results obtained by the use of various techniques on the applications of the fractal concepts and methodology to the description of the morphology developed by humic substances under various experimental conditions, and of the underlying aggregation processes, are discussed. This discussion is preceded by a brief introduction to fractal theory and fractal analyses, with focus on the fractal description of aggregation processes. General conclusions, including both the advantages and limitations of the fractal approach, are outlined, and recommendations are made for additional work using the fractal approach for studies of humic substances.