High temperature foam stability is an important property of foam. In order to better control the stability of foam, this paper systematically reviewed the decay mechanism of foam and the factors affecting foam stability, and introduced the evaluation methods of test foam performance in detail, and discussed the advantages and disadvantages of each method. At the same time, we are looking forward to the development direction of foam stability research.
The mechanism of foam decay It is generally believed that there are two mechanisms for foam decay: one is the drainage of the liquid membrane; the other is the diffusion of the gas through the liquid membrane. Both mechanisms are directly related to the properties of the liquid film and the interaction between the liquid film and the Plateau boundary.
Drainage of liquid film: The discharge of the liquid film in the foam is the result of mutual squeeze and gravity of the bubbles. The extrusion of the bubble is mainly derived from the surface pressure.
The diffusion of gas through the liquid film is always uneven due to the size of the bubbles. According to the Laplace equation, the gas pressure in the small bubbles in the foam is higher than that in the large bubbles. Under this pressure difference, the gas in the small bubble diffuses into the large bubble through the liquid film, causing the small bubble to become small, so that it disappears, and the large bubble becomes large and eventually ruptures. For bubbles floating on the liquid surface, the gas diffuses directly into the gas phase through the liquid film, causing the foam to decay.
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