Rotational Viscometer (Brookfield Viscometer)

• Rotational Viscometer (Brookfield Viscometer) works by measuring torque on a spindle rotating in fluid.
• Rotational Viscometer (Brookfield Viscometer) measures viscosity of liquids in pharmaceuticals and industries.

Principle:

• Measures the torque required to rotate a spindle at constant speed in the sample.
• The resistance to rotation is a function of the sample’s viscosity.
• $\eta \propto \frac{\text{Torque}}{\text{Angular velocity}}$

Types:

1. Couette-type (coaxial cylinder):

   1. Inner cylinder rotates, outer is stationary or vice versa.
   2. Used for both Newtonian and non-Newtonian fluids.

2. Cone and Plate viscometer:

   1. Ideal for small sample volumes.
   2. High accuracy in measuring shear stress and shear rate.

3. Brookfield viscometer:

   1. Common in pharmaceutical QC labs.
   2. Measures torque on rotating spindle at different speeds.

Applications:

• Suitable for non-Newtonian systems.
• Can measure:
  • Thixotropy (using up-and-down shear curve)
  • Pseudoplastic and plastic behavior
  • Viscosity at various shear rates

Advantages:

• Very versatile
• Measures both Newtonian and non-Newtonian behavior
• Can study time-dependent properties (like thixotropy)

Limitations:

• Calibration and spindle choice are critical
• Requires trained handling

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