Original scientific paper

Geometrical Restrictions of Incoherent Transport of Water by Diffusion in Protein of Silica Fineparticle Systems and by Flow in a Sponge. A Study of Anomalous Properties Using an NMR Field-Gradient Technique

Franz Klammler ; Universitàt Ulm, Sektion Kernresonanzspektroskopie, W-7900 Ulm, Germany
Rainer Kimmich ; Universitàt Ulm, Sektion Kernresonanzspektroskopie, W-7900 Ulm, Germany

Abstract

Geometrical restrictions of incoherent water transport in different aggregated particle systems and in a natural sponge were studied using an NMR field gradient technique. Two series of experiments were carried out.
First, the temperature and concentration dependences of the water diffusion coefficient were measured in aqueous systems of bovine serum albumin and gelatin above and below the bulk-water freezing temperature. The concentrations ranged from dilute solutions to almost dry powders being only partly hydrated. The diffusion coefficient within clusters of overlapping hydration shells is reduced by one order of magnitude compared with that of bulk water. Geometrical restrictions manifest themselves (a) by the obstruction effect observed at high water concentrations, (b) by the topologically two-dimensional diffusion in the network of overlapping hydration shells, and (c) by the percolation threshold appearing at about 15 %b.w. water.
The second series of experiments indicated geometrical restrictions in the sense that the transport behaviour in some special systems turned out to be anomalous. Hydrated protein aerogels were produced by means of a lyophilization/rehydration procedure. For comparison, hydrated silica fine- particles having a similar diameter as the proteins were investigated in addition. In both cases, the spin-echo decays by diffusion suggest anomalous behaviour. The same conclusion was drawn for water percolating through the pores of a natural sponge, i.e. for an incoherent flow process.

Keywords

Hrčak ID:

137188

URI

https://hrcak.srce.hr/137188

Publication date:

15.8.1992.

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