Mechanism of antifoam behavior of solutions of nonionic surfactants above the cloud point

Abstract

Aqueous solutions of nonionic surfactants exhibit low foaming above their cloud point, a temperature above which the homogeneous solution separates into two phases: a dilute phase containing a low surfactant concentration and a coacervate phase containing a very high surfactant concentration (e.g., 20 wt% surfactant). In this work, foam formation was measured for the dilute phase, the coacervate, and the mixed solution using the Ross-Miles method for nonylphenol polyethoxylates with 8, 9, or 10 ethylene oxide moieties per molecule. The dilute phase showed no antifoam effect above the cloud point if the coacervate phase was not present, and the coacervate phase foamed little in the absence of the dilute phase. The coacervate phase acts as an oil droplet antifoam to the dilute phase. From surface and interfacial tension data, entering, spreading, and bridging coefficients for this system make it appear probable that the coacervate phase is forming bridges across the film lamellae of the dilute-phase foam and acting to suppress foam formation through the bridging mechanism.

Sol–gel chemistry mediated Zn/Al-based complex dispersant for SWCNT in water without foam formation

“…Non-covalent methods using surfactants [7,8] and polymers [9,10], and covalent chemical functionalization [11] have been widely used to disrupt the bundle structures in aqueous media. One of the major drawbacks of using surfactants and polymers is foam formation, which is not environmentally friendly, causing serious hurdles in industrial application [12,13]. Chemical functionalization, which is quite efficient for dispersing SWCNT, affects their electronic properties due to sp 3 hybridization of C-atoms [14], diminishing electrical conductivity, which is a disadvantage of this method.…”

Thermal destabilisation of bitumen-in-water emulsions – A spinning drop tensiometry study

“…The observation that larger droplets of surfactant-rich coacervate are formed in the presence of salt, combined with the findings of Chaisalee et al [21], suggests the possibility that the coacervate has a destabilising action on bitumen-in-water emulsions. Additionally, the same authors determined the interfacial tension for the dilute aqueous and coacervate phases to be the same as our bitumen/aqueous phase values for NP(EO) 8 and NP(EO) 10 , which suggests that the coacervate phase dictates the bitumen interfacial tension above the surfactant cloud point.…”

“…[21]. These workers were interested in the foam suppression effect of coacervate droplets, since, at temperatures exceeding the cloud point, foams produced from solutions of these surfactants were very unstable.…”

“…Conceivably it involves both kinetic and thermodynamic factors related to the nature of the oil phase and the ability of the surfactant to stabilise the inverse water-in-oil (w/o) emulsions at high temperature. In this latter regard, demulsification of the w/o emulsions by phaseseparated coacervate droplets may occur, as has been invoked for their action as antifoam agents [21].…”

Mechanism of bubble coalescence induced by surfactant covered antifoam particles

“…However, they are not yet found to be as efficient as oil-based antifoams. The nonionic surfactant antifoams have been discussed by several authors [4][5][6][7][8][9][10][11]. These are often called cloud point antifoams since they have a temperature at which the surfactant starts to separate from the aqueous phase forming a coacervate phase.…”