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UBC Theses and Dissertations

Liquid content predictors for aqueous foams Lapucha, Joanna


Historically, foam studies have focused on foamability, foam stability, and foam inhibition as opposed to foam density. Hence, the impact of various factors on foam density is still not well understood. Previous experimental work shows that concentrated surfactant solutions with similar surface tensions produce foams with different liquid fractions. These results contradict the common assumption held that these foams would have near-identical liquid fractions. Therefore, this study probes for correlations between equilibrium and dynamic surfactant adsorption parameters at air-liquid interfaces for aqueous foams made from solutions well above the critical micelle concentration. A protocol was developed for measuring foam density using a cylindrical foaming apparatus with porous filter plate for gas sparging. The foams were created from aqueous solutions of small-molecule surfactants known to have negligible surface shear viscosity. Equilibrium parameters of the maximum surface concentration, equilibrium adsorption/desorption rate constant, and effectiveness (critical micelle concentration) showed weak evidence of a correlation as quantified by linear and ranked correlation coefficients. The surfactant efficiency (concentration needed to reduce the surface tension 20 mN/m) showed some evidence of linear correlation between the ranking of the variables. In contrast, the time required to reduce the surface tension 35% and 50% of the way from the pure water value to the equilibrium value (t_35 and t_50) showed strong evidence of correlation of increasing liquid fraction with faster surfactant adsorption times. The results of this study highlight the influence of dynamics even for highly concentrated surfactant solutions.

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