title: Partitioning of humic acids between aqueous solution and hydrogel: concentration profiling of humic acids in hydrogel phases.
abstract: The partitioning of the natural polyelectrolyte humic acid (HA) from an aqueous dispersion into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) is explored. In both gels, the spatial distribution of HA in the gel body, as measured by confocal laser scanning microscopy, is markedly nonhomogeneous. A striking feature is the enhanced accumulation of HA in a thin film of thickness ca. 15 μm at the surface of the gel body, resulting in average local concentrations that are, for PAAm and alginate respectively, a factor of 10 and 4 greater than that in the bulk solution. The time dependence of accumulation in the surface film is predominantly controlled by the diffusive supply of HA from the aqueous medium, with a time constant on the order of 10(3) s for both gels. The concentration of HA within the bulk gel body differs significantly from that in the bulk aqueous medium: substantially higher for PAAm but much lower for alginate. The results are significant for understanding the nature and rate of sink/source functioning at permeable phases in contact with aqueous media, e.g., biofilms and gel-like layers at biological interfaces or employed in chemical speciation sensors.
authors: Laboratory of Physical Chemistry and Colloid Science, Wageningen University , Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
authors: Katarzyna
authors: K
authors: Zielińska
authors: Raewyn M
authors: RM
authors: Town
authors: Kamuran
authors: K
authors: Yasadi
authors: Herman P
authors: HP
authors: van Leeuwen