Relationship between the continuous phase viscosity and the membrane permeation rate in premix membrane emulsification using Shirasu porous glass membranes

Emulsion viscosity and membrane permeation rate (MPR) are the major factors influencing the wall shear stresses in the membrane pores. However, the effect of the discrete phase viscosities and their relationship with the MPR is not well elaborated. The relationship between droplet size and the continuous phase viscosity at different MPRs was investigated. At higher MPR, the emulsion droplet size was observed to decrease with continuous phase viscosity due to the increase in the wall shear stress in the pores, as the thickness of the lubrication layer between the droplets and the pore walls increases with viscosity. While at low MPR, the droplet size increased with viscosity due to coalescing as the rate of surfactant diffusion onto the interface of the new droplets reduced. The MPR was observed to complement or contrast the effects of the continuous phase viscosity on droplet formation in the membrane pores, depending on its relative magnitude.