Related Experiment Video
Updated: Sep 20, 2026

Studying Surfactant Effects on Hydrate Crystallization at Oil-Water Interfaces Using a Low-Cost Integrated Modular Peltier Device
Published on: March 18, 2020
The effect of surfactant on the efficiency of shear-induced drop coalescence
Steven D Hudson1, Alex M Jamieson, Brian E Burkhart
1Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8544, USA. steven.hudson@nist.gov
Abstract:
The volume-averaged shear-induced drop-coalescence efficiency epsilonv is measured by in situ videomicroscopy of blends of poly(propylene glycol) and poly(ethylene glycol), emulsified with poly(ethyleneglycol-b-propyleneoxide-b-ethyleneglycol) block copolymer surfactant. Adsorption of copolymer to the immiscible blend interface is indicated by a reduction in the interfacial tension, measured by the drop retraction method. The effects of temperature, copolymer molecular weight, copolymer concentration, and capillary number Ca are explored. At small Ca, epsilonv is essentially independent of shear rate and drop size, and depends mainly on the solubility, diffusivity, and surface pressure of the surfactant, indicating that drop trajectories during flow are perturbed by surfactant Marangoni stresses that are controlled by the diffusion-limited sorption of surfactant. At larger Ca, epsilonv 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 the surfactant, though significant, saturates even while the amount of surfactant adsorbed to the interface is quite small. Governing dimensionless parameters, associated material parameters and the behavior of more insoluble surfactants are discussed.
Related Concept Videos
Micelles
Surface Tension of Fluid
Surface tension varies with...
Factors Affecting Dissolution: Particle Size and Effective Surface Area
Surface Tension, Capillary Action, and Viscosity
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
Surface Tension
Excess Pressure Inside a Drop and a Bubble

