The Effect of Surfactant on the Efficiency of Shear-Induced Drop Coalescence
Steven D. Hudson, A M. Jamieson, B Burkhart
Shear-induced drop coalescence efficiency e is measured by in situ videomicroscopy of emulsions of poly(propylene glycol) and poly(ethylene glycol), with poly(ethyleneglycol-b-propyleneoxide-b-ethyleneglycol) block copolymer surfactant. Sorption of copolymer to the immiscible blend interface, as indicated by reduction in the interfacial tension, is measured by the drop retraction method. The effects of temperature, copolymer molecular weight, copolymer concentration and capillary number Ca are explored. At small Ca, e is essentially independent of shear rate and drop size, and it depends mainly on the solubility, diffusivity and surface pressure of the surfactant, indicating that drop trajectories during flow are perturbed by surfactant and are controlled by its diffusion-limited sorption. At larger Ca, e approaches zero. This arrest of coalescence is associated with the onset of slight deformation of the drops during their collision, and drainage of a film of continuous fluid between them.The effect of surfactant, though significant, saturates even while the amount of surfactant adsorbed to the interface is quite small. Governing dimensionless parameters and associated material parameters are discussed.
adsorption, coalescence, drop collisions, emulsions, film drainage, Marangoni stress, Peclet number
, Jamieson, A.
and Burkhart, B.
The Effect of Surfactant on the Efficiency of Shear-Induced Drop Coalescence, Journal of Colloid and Interface Science, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852090
(Accessed December 10, 2023)