Modeling of bubble coalescence in saline water in the presence of flotation frothers

• The lifetime of small foam films from dilute surfactant solutions was modeled.
• Decreasing critical rupture thickness with concentration was predicted correctly.
• The degree of agreement between model and experiment was surfactant specific.
• The important role of an additional non-DLVO attraction force was demonstrated.

This paper proposes a model based on the capillary wave theory of Valkovska, Danov and Ivanov to predict the lifetimes (τ) of small foam films confined between air bubbles in saline water containing flotation frothers such as sodium dodecyl sulfate (SDS), polypropylene glycol (PPG) with a molecular weight of 400, and methyl isobutyl carbinol (MIBC). The model considers the important issues of intersurface force, bubble size, surface tension, and film radius. The predicted τ values of these foam films were compared to the experimental ones. Under the assumption of tangentially immobile film surfaces, excellent agreement between model and experiment for τ was obtained for SDS and PPG, whereas τ was slightly under-predicted for MIBC. The model can be improved by adding an adjustable parameter that is related to the lateral diffusion constant and surface concentration of frother molecules at the air/water interface.

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