消泡剂气/液界面膜的性质对其消泡性能的影响

参照消泡试验标准ASTM E2407,评价了硅油类、聚醚酯类及聚醚改性聚硅氧烷类3种消泡剂的消/抑泡性能,并采用LB膜天平,测试了消泡剂对模拟起泡体系扩张模量、扩张弹性和扩张黏度的影响。结果表明,消泡剂分子吸附在气/液界面上,降低了界面膜的弹性,减小了界面膜的强度,使得界面膜厚度变薄,泡沫寿命缩短,从而达到破泡效果;消泡剂存在下的界面膜强度在一定时间内不足以形成稳定的泡沫,从而达到抑泡效果。同种消泡剂,在一定质量分数范围内,随质量分数增加,界面膜扩张模量、扩张弹性均降低,消泡剂消/抑泡性能变好;超过某一质量分数时,界面膜扩张模量、扩张弹性基本保持不变,消/抑泡性能也不再增强。不同种消泡剂,界面膜扩张模量及扩张弹性降低幅度越大,消/抑泡性能越好。因此,扩张模量和扩张弹性可以很好地解释消泡剂的消/抑泡效果。

Properties of gas/liquid interfacial film formed by defoamer and its influence with respect to performance of the defoamer

The defoaming and foam inhibiting performance of three kinds of defoamer (silicone oil, poly ether ester, and poly ether modified poly siloxane) were assessed according to defoaming test standard ASTM E2407; and the influence with respect to dilational modulus, dilational elasticity and dilational viscosity of the simulated foaming system by different defoamers were tested with LB balance. Results showed that the defoamer molecules are adsorbed on the gas/liquid interfacial film, which weaken the elasticity and the strength of the interfacial film, as well as attenuate the thickness of the film; thus result in shortening of foam existing time and finally foam rupture. Under the existing of defoamer molecules, stable foam layer cannot be formed within a certain time period due to the strength weakening of the interfacial film and thus result in the foam inhibiting effect. Within a certain mass fraction range, the higher the mass fraction of the same defoamer, the lower the interfacial film dilational modulus and dilational elasticity, and the better of the performance of defoaming and foam inhibiting. When the mass fraction exceeds a certain value, the interfacial dilational modulus and dilational elasticity essentially keep no change, and the performance of defoaming and foam inhibiting shows no more enhancing. For different types of defoamer, the higher amplitude of reduction capacity of interfacial film dilational modulus and dilational elasticity of the defoamer, the better performance of defoaming and foam inhibiting. Therefore, dilational modulus and dilational elasticity are correlated to defoaming and foam inhibiting performance of the defoamer.