WATER TRANSPORT BY A SPREADING SURFACTANT IN FINE DISPERSE MATERIALS

A surface active substance (surfactant) spreads on the water film lying on the surface of fine disperse materials (clay, oxides), with lower velocity than on the surface of bulk water and on coarse materials (sand).

The spreading surfactant carries the underlying water although the surface is not continuous and water is present as a thin film.

The ratio of the transported water to the spread surfactant decreases with increasing specific surface, being > 10⁴ on sand surface and < 10 on fine disperse materials (clay, oxides).

The amount of transported water increases with increasing specific surface and increasing water film thickness. The driving force for water transport is the surface pressure; the presence of another surfactant is therefore prejudicial for the spreading and transport of underlying water.

The water transport by the spreading surfactant is accompanied by the streaming potential, which is inversely related to the specific surface.