EVALUATION OF DYNAMIC VISCOSITY OF TURBID FLUIDS USING OPTICAL COHERENCE TOMOGRAPHY
A method for evaluating the viscosity of turbid biological fluids and pharmaceuticals is described. The proposed method is based on digital offline analysis of optical coherence tomography (OCT) raw data. The scanning probe of the OCT-system is positioned perpendicular, a drop of a tested liquid is applied to a scanning probe of the system, so that it hangs freely from its surface under the action of surface tension and gravity. Then, a movable glass slide touches the lower part of the drop ensuring minimal contact. In a correct experiment, the contact area of the upper side (base) of the drop with the solid surface of the scanning probe should be many times larger than the contact area of the lower side of the drop with the movable glass slide. The first three-dimensional structural OCT-image (C-scan) is obtained in the above-described position. The movable slide is driven in perpendicular direction to the scanning probe. A series of three-dimensional structural OCT-images of a deformed drop is acquired during the slide displacement. The deforming surface area is calculated as the area of the corresponding segment of the first C-scan. The magnitude of the deforming force for different moments is calculated based on the characteristics of the controlled motion of the movable plate. The ratio of the deforming force to the area of the deforming surface allows estimating the shear stress at the corresponding moments of time. The shear rate is estimated from the displacement C-scan control points of the drop surface for the known time periods of each deforming step. The dynamic viscosity is estimated by the classical formula, as the ratio of shear stress to shear rate. The results are digitally processed, averaged, are to be used in dynamic viscosity determination and presented to the end user.
Tambov State Technical University
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