Effect of oil on foam stability: Aqueous foams stabilized by emulsions

Abstract

The interactions between oil drops and the foam lamella were investigated by following the aging phenomena (i.e., drainage, bubble disproportionation, and rupture) of foams containing emulsified oils. It was found that the stability of the film (“pseudoemulsion film”) between an oil drop and an air/water surface was an important factor for the stability of foams containing emulsified oils. The mechanism of foam stability in the presence of stable emulsions was investigated for the case where the pseudoemulsion film was stable. It was found that these emulsions accumulated within the Plateau borders of the draining foam, thus inhibiting foam drainage. As a result, the foams were found to be stabilized by emulsified oil. Important parameters which affect foam stability, such as oil volume fraction, drop size, and oil phase density, were identified and the effect of these parameters on foam stability was experimentally verified. It was found that the stability increased with the oil fraction in the foam. The foam stability was found to go through a minimum as a function of drop size, due to competing effects of emulsion viscosity at smaller drop sizes and the higher accumulation of oil at larger drop sizes. The density of the oil phase directly influenced the oil accumulation and thus the foam stability.