Measuring Inter-Particle Forces at an Interface with Optical Tweezers and a Long Working-Distance Objective Lens

An optical tweezer set up is used to measure the forces between polystyrene microspheres on the interface between mineral oil and water. The trap is controlled through Matlab Simulink and dSpaceControlDesk. The forces were found to follow a combination of Coulomb's law and dipole-dipole interaction, but for much less charge than is specified by the manufacturer to be on the surface of the microspheres. There is also a value given for the effective viscosity of the interface. A discussion on the design andmotivation for using a Bessel beam trap can be found in the appendix