Water-Glycerol Mixture Viscosity through Optical trapping


A cellular medium is highly viscoelastic in nature. In order to understand the viscoelastic nature of a medium, we have developed a new simple approach to quantitatively measure the viscosity of water-glycerol mixture medium using an optical tweezers technique. In this approach, the position of a trapped bead of radius r in a glycerol-water mixture is measured using a position sensing diode with 40 kHz acquisition rate. By using a Lorentzian fit to the Power Spectrum of the position signal, the corner frequency is obtained. For a small change in volume concentration of glycerol in a water-glycerol medium, the change in trap stiffness can be ignored if incident laser power and bead radius remain unchanged. By following an iterative experimental approach, the viscosity of the water-glycerol mixture can be obtained by comparing the corner frequencies obtained experimentally in a medium of known viscosity. Using this approach, the viscosity of a water-glycerol mixture has been measured for glycerol volume concentration of 10%, 20%, 30%, and 40%. The experimental results are compared with the work of Segur and Oberstar [1] as well as with a simple theoretical approach that models the data behavior versus glycerol concentration. The comparison shows that with this experimental approach using an optical tweezers technique, the viscosity of water-glycerol mixture is determined to an accuracy of 0.0082 percent. [1] J. B. Segur and H. E. Oberstar, Industrial & Engineering Chemistry, V43, No. 9 (1951), p2117.


Physics, University of West Georgia

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