Role of antifoam spreading

In a number of works dedicated to defoaming, Ross et al. [16,37] have come to the conclusion that there are several different effects of antifoam spreading on foam stability. One of them is the monomolecular spreading of the antifoam which is equivalent to the adsorption 

Defoaming ability of antifoams with different spreading coefficients in OP-10 and sulphonol foaming systems 

Comparison of the spreading and entering coefficients with the stability of non-symmetric films has been considered by Lobo and Wasan [52]. The results are presented in Table 9.4. 

It is seen that for all but one of the systems (NaDoS + benzene) E and S are positive, i.e. the oil spreads on the surface of the foaming solution and enters the surface through the water core. However, the observations of the behaviour of microscopic aqueous films on hydrocarbon substrates showed that in all systems these films were stable. 

Prins [in 20] has suggested that antifoams that do not spread under equilibrium condition can spread at non-equilibrium values of the surface tension. Garrett et al. [20] have illustrated that the effective antifoams they studied (mixture of liquid paraffin and hydrophobed silica) did not spread during surface stretching and decrease the surface tension by 20 mN m 1. So, here again it was proved that the condition of spreading was not necessary to achieve defoaming. 

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