Foam Stability and Foam Breaking

Foam Stability and Defoaming In any production process, liquids subjected to physical or chemical stress tend to foam. Foam formation is generally an undesired event because it negatively affects process speed and capacity. To eliminate the adverse effects of foam on the process or product, various chemicals are used that either suppress existing foam and/or prevent foam formation. These chemicals are referred to by names such as antifoam, defoamer, and foam inhibitor, which are often used interchangeably although there are some nuances among them. One of the priorities in developing a good defoamer formulation is understanding the physicochemistry of foam and its response to specific variables. Knowing which variables enable foam to persist allows us to intervene in these variables with chemicals having specific properties and provides the opportunity to eliminate foam. At this point, foam stability is an important topic that warrants attention. Due to its chemical nature, foam is actually an unstable structure, but it can persist without collapsing for a period of time due to surface elasticity, viscous drainage, reduced gas diffusion between foam bubbles, and thin film stabilization effects arising from the interactions of opposing surfaces. Foam stability can be interpreted through Gibbs elasticity, a widely accepted parameter in the literature. Gibbs elasticity, which results from the reduction in the concentration of surfactants at equilibrium following the expansion of the film layer, increases the equilibrium surface tension that causes foam stability.

In the equation, "E" represents Gibbs elasticity. "A" is the surface area of the foam while "σ" is the equilibrium surface tension. The interconnected nature of foam surfaces requires considering the Marangoni effect, which is a function of time, when interpreting foam stability.

  The Marangoni effect describes mass transfer resulting from surface tension gradients between the surfaces of two liquid components with different chemical compositions. Parameters such as these provide us with case-specific data, enabling meaningful interpretations regarding the situation requiring intervention and laying the foundation for creating situation-specific defoamer formulations for the most effective solution. As is known, pure liquids do not foam. For foam to form and remain stable, several components with suitable chemical structures must come together and maintain this state. From this statement, it is easily understood that removing some of the content that creates foam and/or supports its stability results in the foam collapsing. As a basic mechanism, the first step in this process is the defoaming chemical coating the foam surface. The primary property determining how effectively foam will be suppressed is the surface tension of the foam, the liquid, and the interface. Due to the nature of the process, the surface tension of the defoaming liquid must be lower than that of the foaming liquid. In this way, the defoamer coating the foam creates a composition change in the foam and causes it to collapse. Another mechanism exploited in foam elimination is bursting the foam rather than suppressing it. Operating in a manner similar to bursting soap or detergent foam by touching it with a dry finger, in this mechanism the defoaming chemical is designed to cause a localized reduction in surface tension. The localized decrease in surface tension, which is one of the main sources of foam stability, creates a weak point at the location where the defoaming chemical contacts the foam, bursting it in a manner similar to how a needle bursts a balloon. To summarize, intervention in unwanted foam formation can be more effectively carried out by correctly analyzing the variables causing the issue and the underlying mechanisms using appropriate methods, interpreting the results correctly, and making decisions regarding the most suitable defoamer composition. Hasancan Dağlar / Chemical Engineer / Operations Manager / Dağlar Polimer Kimya

References Bonsu, K., Shokri, N., Grassia, P., 2015: Foam stability in the presence and absence of hydrocarbons: Foam bubble- to bulk-scale. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 481, 514-526. Wang, C., Li, H.A., 2016: Stability and mobility of foam generated by gas-solvent/surfactant mixtures under reservoir conditions. Journal of Natural Gas Science and Engineering, 34, 366-375. Fink, J.K., 2003: Defoamers. Oil Field Chemicals, 21, 316-324