Foamed emulsion drainage: flow and trapping of drops

Abstract

: Foamed emulsions are ubiquitous in our daily life but the ageing of such systems is still poorly understood. In this study we investigate foam drainage and measure the evolution of the gas, liquid and oil volume fractions inside the foam. We evidence three regimes of ageing. During an initial period of fast drainage, both bubbles and drops are very mobile. As the foam stabilises drainage proceeds leading to a gradual decrease of the liquid fraction and slowing down of drainage. Clusters of oil drops are less sheared, their dynamic viscosity increases and drainage slows down even further, until the drops become blocked. At this point the oil fraction starts to increase in the continuous phase. The foam ageing leads to an increase of the capillary pressure until the oil acts as an antifoaming agent and the foam collapses.

A review of aqueous foam in microscale

“…In addition, foams absorb the oil and pollutants in the decontamination process [85]. The effect of the oil on the foam stability is main interest since the oil droplets can affect the efficiency in those applications [86][87][88][89]. The oil can be introduced to the foam from beginning.…”

“…The oil can be introduced to the foam from beginning. The mixture of the gas bubbles and oil drops dispersed in water is called foamed emulsions or foamulsions [29,86]. A sample of foamulsion is shown in Fig.…”

“…31.a. [86].The emulsion drops are located in the spaces between the bubbles and can affect the properties of the foam significantly. However, adding oil drops to a foam is a well-known method to suppress the foam and destabilize it [17].…”

Scaling law for the kinetics of water imbibition in polydisperse foams

“…36 In the case of emulsions or colloidal suspensions, dispersed oil droplets or solid particles are trapped in the water paths in the foams, which reduces the rate of drainage compared to that without droplets or solid particles. [39][40][41] Imbibition of liquid into a foam occurs owing to the capillary pressure of the Plateau border, and comparison with the gravity effect is the key to imbibition on earth. 42,43 Microgravity has been investigated in liquid imbibition to minimize the effect of gravity, [44][45][46][47][48][49][50] in which the bubbles are very stable and coarsening or coalescence does not occur.…”

“… 36 In the case of emulsions or colloidal suspensions, dispersed oil droplets or solid particles are trapped in the water paths in the foams, which reduces the rate of drainage compared to that without droplets or solid particles. 39–41 …”