Stability Factors of Foam Film in Contrast to Fluctuation Induced by Humidity Reduction

We have examined the relationship between dynamic surface properties of aqueous SDS solutions and foam film stability by observing the dynamic surface tension (gammat ), elongation of the lamellae (L lamellae ), and the thickness of the lamellae measured by FT-IR. Three foam film models were used by controlling such factors as the Marangoni effect by changing the SDS concentration, the disjoining pressure with the addition of electrolytes, and the surface viscosity with the addition of glycerin. In order to obtain information about the most effective factor in foam film stability, the lifetime of these films was measured under the circumstances of low relative humidity, at which vigorous fluctuation occured in the foam film. Foam film stability was found to be remarkably enhanced by the Marangoni effect and surface shear viscosity in a thin aqueous film at a relative humidity between 60 and 75%. Under these conditions, mild fluctuation would occur in the films. On the other hand, foam film stability was found to be maintained by the disjoining pressure in a thin aqueous film at the humidity below 60%. Under these conditions, vigorous fluctuation would occur in the foam film. It is concluded that foam film stability of an ionic surfactant solution mainly depends on the disjoining pressure which generates a repulsion force between the two surfaces in contrast to the vigorous fluctuation induced by humidity reduction.