(171o) A Viscosity Measurement Technique for Ultra-Low Sample Volumes | AIChE

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(171o) A Viscosity Measurement Technique for Ultra-Low Sample Volumes

Authors 

Tirumkudulu, M. - Presenter, Indian Institute of Technology Bombay
Mir, M. A., Indian Institute of Technology Bombay
Viscosity refers to the resistance offered by a fluid to shear and is one of the most fundamental physical property of fluids. The importance of viscosity measurement lies in its ability to provide critical insights into fluid behaviour and performance, which impacts product quality and process efficiency in industrial applications. Measurement of viscosity of biological fluids is increasingly becoming important in medical diagnostics.

The instruments for measuring viscosity may be broadly classified into Viscometers (capillary tube, falling ball, and rotating viscometers) and Rheometers. While the former measures only the viscosity, the latter probes several rheological properties of fluids. Of the three categories of viscometers, only the rotating viscometers exhibit viscometric flows with infinitesimal fluid elements in steady state, simple shearing motion. Irrespective of the technique, the measurement of low viscosity liquids has always been a challenge.

Here, we demonstrate a cost-effective and robust method that uses microlitre liquid volumes to measure low viscosities. A liquid drop of fixed volume is placed on a substrate and is smeared by a contacting blade moving at constant speed. The thickness of the film is determined by the capillary number, which measures the competition between the viscous force that smears the liquid over the glass slide and the surface tension that resists the deformation of the interface. We show that the length of the smear for a fixed sample volume is also set by capillary number and can be used as a reliable measure of fluid viscosity. The viscosity measured for a number of liquids and suspensions in the viscosity range of 1-15 mPa.s matches closely with that obtained from a rheometer.. The technique is especially suitable for viscosity measurements of biological fluids where viscosities are low and sample sizes are small. The technique can detect small changes in blood viscosity enabling it to be used as a screening tool for diseases and therapeutic interventions.

Topics 

Transport Phenomena

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