Zero-Shear-Rate Viscosity Measurements for Polymer Solutions by Falling Ball Viscometer Method (CAT#: STEM-VTT-0004-ZJF)

The principle of the falling ball viscometer is to determine the falling time of a sphere with known density and diameter within a fluid filled inside glass tube. The viscosity of the fluid sample is related to the time taken by the sphere to pass between two specified lines on the cylindrical tube. The determination of dynamic viscosity of Newtonian liquids using a suitable falling ball viscometer is performed at 20 ± 0.1 °C, unless otherwise prescribed. The time required for a test ball to fall in the liquid to be examined from one ring mark to the other is determined. If no stricter limit is defined for the equipment used the result is valid only if 2 consecutive measures do not differ by more than 1.5 per cent.

Non-Newtonian Fluid Mechanics

1. Fill the clean, dry tube of the viscometer, previously brought to 20 ± 0.1 °C, with the liquid to be examined, avoiding bubbles.
2. Add the ball suitable for the range of viscosity of the liquid so as to obtain a falling time not less than 30 s.
3. Close the tube and maintain the solution at 20 ± 0.1 °C for at least 15 min. Let the ball run through the liquid between the 2 ring marks once without measurement.
4. Let it run again and measure with a stop-watch, to the nearest one-fifth of a second, the time required for the ball to roll from the upper to the lower ring mark. Repeat the test run at least 3 times.
5. Calculate the dynamic viscosity η in millipascal seconds.

• Falling ball viscometer: Usually consists of: a glass tube enclosed in a mantle, which allow precise control of temperature; six balls made of glass, nickel-iron or steel with different densities and diameters. Commercially available apparatus is supplied with tables giving the constants, the density of the balls and the suitability of the different balls for the expected range of viscosity.
• Sample liquid