Studies of a Colloidal System Using Optical Tweezers and Digital Video Microscopy

This project utilizes the optical tweezer system combined with digital video microscopy to study the behaviour of a polystyrene micro-sphere and a pair of micro-spheres (dimer) suspended in a dilute medium. Our experimental study of the relation between the shapes of the solute molecule and their translational diffusion has provided us an excellent test of the experimental methodology and digital video microscopy. We are also interested in investigating the rotational Brownian motion of a dimer confined in two-dimensional plane and measuring its rotational diffusion coefficient. From the results, we could verify the effect of two different molecular shape on their translational diffusion coefficients. It is also observed that the measured diffusion coefficient is lower than its theoretical value. The explanation for this observation is included in our report discussion