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MEASURING VISCOSITY OF A LIQUID BY ANALYZING BROWNIAN MOTION OF MICRO-SIZED PARTICLES IN AN OPTICAL TWEEZERS

autorzy: Nguyen Thi Ngoc, Nguyen Thao Nguyen, Vi Luong Mai, Nguyen Hoang Dam Thuyen, Le Doan Thai, Tran Cong Trien

Recently, we have successfully constructed an optical tweezers to control motion of micro-size spherical particles in a liquid. However, in the absence of lasers, the motion of these particles is Brownian motion. Therefore, the viscosity of the liquid containing these particles can be deduced if their velocities versus time are known. This is possible by using the setup of the optical tweezers, videos of Brownian motion of the particles can be recorded and analyzed to obtain such parameters with very small volume (about microlite). Determination of viscosity is an important condition for measuring the optical force of particles, biological samples in optical tweezers. In this work, we demonstrate the use of this technique to determine the viscosity of water by analyzing the Brownian motion of 1.01m-silica particles. The obtained value is reasonable with about 3.3% off from its known one.