Optical tweezers are tightly focussed laser beams that are used to pick up and manipulate micron-sized objects, such as cells or polymer beads. If optical tweezers are used to oscillate a particle, the amplitude and phase of the particle’s motion tell you about the forces acting on the particle. We have developed the idea of oscillating tweezers to measure hydrodynamic interactions and interparticle forces between colloidal particles or oil droplets in water. This work was conducted in collaboration with Dr. Andrew Ward of the Central Laser Facility at the Rutherford Appleton Laboratory.
We have also used optical tweezers to manipulate the shape of heptane droplets. Under normal conditions the high interfacial tension of the heptane droplets would overwhelm the small forces exerted by the tweezers. However, through the use of the surfactant AOT the interfacial tension of the droplet can be brought into the ultralow regime (µN/m). Using multiple optical traps we were then able to stretch the droplets into a variety of different shapes.
1. C. D. Mellor, M. A. Sharp, C. D. Bain and A. D. Ward "Probing Interactions between Colloidal Particles with Oscillating Optical Tweezers" Journal of Applied Physics 2005, 97, 103114/1–11 (DOI).
2. A. D. Ward, M. G. Berry, C. D. Mellor, C. D. Bain "Optical sculpture: controlled deformation of emulsion droplets with ultralow interfacial tensions using optical tweezers" Chemical Communications 2006, 4515-4517 (DOI).