Theoretical analysis for the optical deformation of emulsion droplets
Abstract
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.
Document Type
Journal Article
Date of Publication
1-1-2014
Faculty
Faculty of Health, Engineering and Science
Publisher
Optical Society of America
School
School of Engineering
RAS ID
17581
Copyright
free_to_read
Comments
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. Available here