A defoamer is an agent added to a liquid to remove surface foam and help release trapped air. These agents are common in many foaming liquids such as cooking oil and laundry soap. They are also common in a wide range of industrial processes ranging from oil refining to wastewater treatment. In most cases, a deformer is placed in a water or oil mixture before being placed into the liquid. These mixtures help to distribute the defoamer evenly through the liquid and often promote a specific type of air removal.
Foam is the layer of bubbles that rises to the top of a liquid. Regardless of the liquid, the bubbles operate the same way. Air becomes trapped in the liquid and slowly combines to form a bubble. The bubble will rise to the surface where it will collect in a thick layer of bubbles, or foam. It is possible that the foam would instead sink to the bottom, if the liquid were somehow lighter than air.
When air is trapped in certain liquids, it can cause a problem when those liquids are processed. For example, if dishwasher detergent had the same foaming capacity as normal dish soap, the suds would rapidly overflow the dishwasher. In addition, the rinsing action of the dishwasher would be insufficient to remove the soap residue.
These substances use a defoamer to keep the foam at a reasonable level. They do this by releasing air trapped in the liquid and weakening the surface tension of existing bubbles so they pop easier. Generally, water-based defoamers are better at removing trapped air, and oil-based ones work better on actual foam removal. A third type of defoamer, silicon-based, has specific properties that mimic water- and oil-based that allow it to work effectively on non-aqueous liquids such as crude oil.
An oil-based defoamer is generally insoluble within the foaming liquid. This means that it stays in a thin layer on the top of the substance where it comes into contact with potential foam bubbles. In order for the foam to form on the liquid’s surface, it has to pass through the defoamer intact. The oily layer prevents this and allows the air to escape while leaving the bubble material in the liquid.
Water-based defoamers are usually soluble within their liquid. These agents mix directly with the material and help to collect trapped air. This air will rise to the surface surrounded by the defoamer rather than the parent liquid. When the bubble reaches the surface, the defoamer pops easily and the air is released.