Viscometer torsion pendulum

One of the main drawbacks of the torsion pendulum viscometer is that it uses a range of shear rates and hence it is not suitable for measurement of non-Newtonian films. In the latter case, it is preferable to use the rotational torsional viscometer. The surface film is sheared between rotating concentric rings on a surface. The shear rate can be held constant by rotating one ring, while measuring the torque T on the other ring (28) i.e.. 

The torsional pendulum of a dense disk moving slowly in a viscous medium has been developed by J. Kestin and co-workers about 1980 to measure simultaneously the density and the viscosity of the fluid [5.11]. This work was based on a couple of papers reporting on oscillating body viscometers using cups, spheres, cylinders, etc. published already in the period 1930-1960 [5.12]. Today pendulum viscosimeters are used to measure the viscosity of both gases, liquids, and even molten metals and salts at extreme temperatures (Ir(liquid melting state) 2,800 K) and pressures (100 MPa), [5.13-5.15]. 

The simplest procedure to measure the interfadal shear viscosity is to use a torsion pendulum surface viscometer [55]. This technique observes the damping of a torsion pendulum due to the viscous drag of a surface film. The shearing element can be in the form of a ring, a disc or knife-edged disc, which is suspended by a torsion wire and positioned at the place of the interface (Figure 6.34). Measurements are... 

The surface viscosity may be related to the torsion modulus of the wire, C , the polar moment of inertia of the oscillating pendulum, 7, and the dimensions of the viscometer... 

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