Optical Deformation of Emulsion Droplets

Abstract

Optical tweezers are a useful and fascinating tool for the manipulation of a range of microscopic particles. I describe the set up of optical trapping apparatus, and investigate the use of a spatial light modulator for the creation of arrays of optical traps. Optical deformation of microemulsion droplets has previously been demonstrated for systems with ultra-low interfacial tension. A disadvantage of the systems used was the strong temperature-dependence of the interfacial tension. I have explored options for creating temperature-insensitive microemulsions, and have shown that a mixed surfactant system containing docusate sodium salt (AOT) and pentaethylene monododecyl ether (C12E5) is capable of stabilising a temperature-insensitive microemulsion with very low interfacial tension. With this system I was able to deform droplets across a wide temperature range using dual optical tweezers. I have investigated several methods of producing a monodisperse emulsion with droplet diameters in the region of 5 μm, including microfluidic technology and membrane emulsification. Although I was unable to produce a monodisperse emulsion within the scope of this project, the work has presented promising future opportunities. A design has been produced for a microfluidic device that will enable trapping and manipulation of emulsion droplets, and will facilitate changing the continuous phase composition.