title: The growth of fractal humic acids: cluster correlation and gel formation.
abstract: The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and II), has been studied using small-angle neutron scattering at an acidity corresponding to pH 5.0 and 0.10 M ionic strength (NaCl). Humic acids aggregate either to large clusters with a fractal dimension of 2.3 and an average diameter of 1720 A (I) or to clusters with an average diameter of 700 A (II). After storage for 2 days at 4 degrees C, the latter aggregates (II) formed a gel. In a step toward gelation, we observed cluster-cluster interaction from the neutron-scattering data in the form of a correlation peak. These differences in size can be explained by assuming that the smaller particles (II) are trapped into a nonequilibrium state characterized by the temperature-solvent condition. The importance of a humic acid gel network for the conservation of water and nutrients in the environment is discussed.
authors: Department of Chemistry, Swedish University of Agricultural Sciences, Uppsala.
authors: R
authors: R
authors: Osterberg
authors: K
authors: K
authors: Mortensen
mesh_terms: D005782:Gels; D006812:Humic Substances / Q000737:chemistry*; D009502:Neutrons; D012987:Soil / Q000032:analysis; D014881:Water Supply / Q000032:analysis
chemical_list: D005782:Gels; D006812:Humic Substances; D012987:Soil