Drag of a laser trapped fine particle in a microregion

To observe hydrodynamics in microregions, we applied laser scanning manipul ation to measure the drag acting on a fine glass bead moving in mineral oil sandwiched between two glass plates (the thickness of the oil layer was a 33 and 64 mu m). We measured the maximum velocity, V-M, of a laser trapped bead at which the bead was released. This allowed us to quantitatively dete rmine the drag, the drag coefficient, C-D, and the Reynolds number, R, of t he particle in the microregion of a viscous fluid. As a result, the minimum CDR was obtained midway between the two glass plates, and the CDR increase d closer to the walls. Also, the distribution of CDR was in good agreement with the values calculated using the equation for wall effect in macroregio ns (over 0.1 mm).