Georgia Journal of Science

Article Title

Optical Tweezer viscosity measurement of glycerol-water mixture


A cellular medium is highly viscoelastic in nature. To understand the viscoelastic nature of a medium, we have taken the first step at developing a new simple approach to quantitatively measure the viscosity of a water-glycerol mixture medium using the optical tweezers technique. Also further theoretical approaches have been developed to model the viscosity behavior. In our optical tweezers system, the position of a trapped bead was measured using a position sensing diode with 40kHz acquisition rate. By using a Lorentzian fit to the Power Spectrum of the position signal, the corner frequency was determined. At constant laser power and at constant bead radius, the trap stiffness is assumed to remain the same for small change in volume concentration of glycerol in a water-glycerol medium, indicating that the change in corner frequency is solely dependent on the medium. Hence, we determined the viscosity of the water-glycerol medium by comparing to the corner frequency of a known viscosity substance. Using this approach, we have measured the viscosity of water-glycerol mixture for glycerol volume concentration of 10%, 20% and 30% at various laser intensities. We compare the results of the modeling as well as the experimental results against each other as well as against known viscosity measurements. The theoretical approach to model the results is based on a modified version of a virtual crystal approximation that involves the mixture's respective substance concentration that yields the correct viscosity of the individual substance at the concentration limits of 0% and 100%.

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