Size methods spreading coefficient

Different oils (mainly hydrocarbons or silicone oils) and their mixtures with hydrophobic solid particles are widely used for destruction of undesirable foam. For a long time, the entry, E, spreading, S, and bridging, B, coefficients (which can be calculated from the oil-water, oil-air, and water-air interfacial tensions) were used to evaluate the activity of such oil-based antifoams (AFs). However, recent studies showed that there was no correlation between the magnitudes of E, S, and B and the antifoam activity—the only requirement for having an active AF, in this aspect, is to have positive E and B. Instead, it was shown that the so-called entry barrier, which characterizes the ease of entry of pre-emulsified oil drops in the solution smface, was of crucial importance an easy entry (low entry barrier) corresponded to an active AF and vice versa. We developed a new method, the film trapping technique (FTT), which allows one for the first time to measme directly the critical capillary pressure, P , which induces the entry of micrometer-sized oil drops, identical to those in real AFs. This chapter describes the main results obtained so far by the FTT with various systems. 

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