Preventing the reformation of foam is a crucial step in achieving effective and long-lasting defoaming action. The hydrophobic PO (Propylene Oxide) chain in EO/PO block co-polymers plays a critical role in this stage. Here’s how it functions:

The main action of the PO chain in preventing foam reformation is called dewetting. Dewetting is an action that drives the separation of the liquid from an area it covered, in this case, the defoamer emulsion droplets on the surface of the foam film. In a sense, it makes that surface repellent to the formation of the foamy liquid.

This action essentially forms a sort of “protective layer” made up of the block polymer’s hydrophobic (water-repelling) part, i.e., the PO chain. Once the foam has been destabilized and collapsed, the PO chain works to keep it that way by repelling any other liquid that would potentially add to the foam.

By altering the surfactant layer on the surface of the foaming medium, the hydrophobic PO chain helps destabilize existing foam and prevent the formation of new foam. In essence, when the PO chain displaces the stabilizing surfactant within the foam lamella, it takes its place, and its water-repelling properties help prevent the reformation of foam.

In addition to the above actions, the PO chain also helps form a protective barrier around remaining bubbles. This protective barrier acts as a shield to prevent the bubbles from joining to form larger, more stable foam structures, thus curbing foam reformation.

In conclusion, the PO chain’s hydrophobic nature is crucial to the long-lasting effectiveness of EO/PO block co-polymers as defoaming agents. This attribute ensures that even after the initial foam has been collapsed, the system remains resistant to foam reformation in the near term. Thus, the defoamer can provide sustained control of foaming.