A constant torque micro-viscometer

Simon John Wyatt Parkin; Gregor G. Knoener; Timo A. Nieminen; Norman R. Heckenberg; Halina Rubinsztein-Dunlop

doi:10.1117/12.590147

14 March 2005 A constant torque micro-viscometer

Simon John Wyatt Parkin, Gregor G. Knoener, Timo A. Nieminen, Norman R. Heckenberg, Halina Rubinsztein-Dunlop

Proceedings Volume 5736, Nanomanipulation with Light; (2005) https://doi.org/10.1117/12.590147
Event: Integrated Optoelectronic Devices 2005, 2005, San Jose, California, United States

Abstract

We present a technique to measure the viscosity of microscopic volumes of liquid using rotating optical tweezers. The technique can be used when only microlitre (or less) sample volumes are available, for example biological or medical samples, or to make local measurements in complicated micro-structures such as cells. The rotation of the optical tweezers is achieved using the polarisation of the trapping light to rotate a trapped birefringent spherical crystal, called vaterite. Transfer of angular momentum from a circularly polarised beam to the particle causes the rotation. The transmitted light can then be analysed to determine the applied torque to the particle and its rotation rate. The applied torque is determined from the change in the circular polarisation of the beam caused by the vaterite and the rotation rate is used to find the viscous drag on the rotating spherical particle. The viscosity of the surrounding liquid can then be determined. Using this technique we measured the viscosity of liquids at room temperature, which agree well with tabulated values. We also study the local heating effects due to absorption of the trapping laser beam. We report heating of 50-70 K/W in the region of liquid surrounding the particle.

Citation Download Citation

Simon John Wyatt Parkin, Gregor G. Knoener, Timo A. Nieminen, Norman R. Heckenberg, and Halina Rubinsztein-Dunlop "A constant torque micro-viscometer", Proc. SPIE 5736, Nanomanipulation with Light, (14 March 2005); https://doi.org/10.1117/12.590147

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