Theoretical and experimental studies of drop size in membrane emulsification – Single pore studies of hydrodynamic detachment of droplets

• We present hydrodynamic model for droplet size prediction under the cross-flow.
• The model is based on interfacial tension, buoyancy and hydrodynamic forces.
• The model can reproduce quite reasonably trends observed in the experiments.
• Orifice surface hydrophobization and DAL causes deviation from model predictions.

Single pore set-up with the drop detachment process observed by high speed CCD camera is a convenient system to study basic processes governing formation of emulsions by cross-flow membrane emulsification. We studied dependence of the droplet size on the volumetric flows of continuous and dispersed phase in square glass cell (10 mm × 10 mm), where the droplets were formed at glass capillary (inner diameter ID = 0.075 mm) or steel needle (ID = 0.3 mm) for selected surfactants: anionic – sodium dodecyl sulphate (SDS), cationic – dodecyl trimethyl ammonium bromide (DDTAB), non-ionic – Tween 80 and oil soluble anionic – docusate sodium (AOT). As oil phases dodecane and cyclohexane were used. We found that the simplified model based on the balance of interfacial tension, buoyancy and hydrodynamic forces can correctly reproduce trends in the dependence of the droplet size on continuous and dispersed phase flow intensity and dynamic interfacial tension. However some effects not accounted for by the model, such as unexpected bubble shape deformation, were also observed and are discussed in the paper.

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