Theoretical analysis for the optical deformation of emulsion droplets

Document Type

Journal Article


Optical Society of America


Faculty of Health, Engineering and Science


School of Engineering




This article was originally published as: Tapp D., Taylor J.M., Lubansky A.S., Bain C.D., Chakrabarti B. (2014). Theoretical analysis for the optical deformation of emulsion droplets. Optics Express, 22(4), 4523-4538. Original article available here


We propose a theoretical framework to predict the three dimensional shapes of optically deformed micron-sized emulsion droplets with ultra-low interfacial tension. The resulting shape and size of the droplet arises out of a balance between the interfacial tension and optical forces. Using an approximation of the laser field as a Gaussian beam, working within the Rayleigh-Gans regime and assuming isotropic surface energy at the oil-water interface, we numerically solve the resulting shape equations to elucidate the three-dimensional droplet geometry. We obtain a plethora of shapes as a function of the number of optical tweezers, their laser powers and positions, surface tension, initial droplet size and geometry. Experimentally, two-dimensional droplet silhouettes have been imaged from above, but their full side-on view has not been observed and reported for current optical configurations. This experimental limitation points to ambiguity in differentiating between droplets having the same two-dimensional projection but with disparate three-dimensional shapes. Our model elucidates and quantifies this difference for the first time. We also provide a dimensionless number that indicates the shape transformation (ellipsoidal to dumbbell) at a value ≈ 1.0, obtained by balancing interfacial tension and laser forces, substantiated using a data collapse.



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