Viscometer cone-n-plate

The major advantages of cone-n-plate viscometers are as follows ... 

The shear stress and primary normal stress measurements can be made simultaneously on the sanqile when it is subjected to unidirectional rotation shear in the gap of a cone-n-plate viscometer. 

The cone-n-plate viscometer can be used for osdllatory shear measurements as well. In this case, the sanq>le is deformed by an osdllating driver which may be mechanical or electromagnetic. The amplitude of the sinusoidal deformation is measured by a strain transducer. The force deforming the sample is measured by the small deformation of a relatively rigid spring or tension bar to wbidi a stress transducer is attached. Because of the energy dissipated 1 the viscoelastic polymer melt, a phase difference develops between the stress and the straiiL The complex viscosity behavior is determined from the amplitudes of stress and strain and the phase angle between them. The results are usually interpreted in terms of the material functions G, G", and others [21-28]. 

The parallel-disk viscometer used for measuring the shear stress and normal stress difference of molten thermoplastics is similar in principle to the cone-n-plate viscometer except that the lower cone is replaced by a smooth circular disk. This type of viscometer was initially developed for measuring the rheological properties of rubber [29-33] and therefore made use of serrated disks placed in a pressurized cavity to prevent rubber slippage. When it was adapted for thermoplastic melts [1534,35], measurements were performed using smooth disks and without pressure. 

Oscillatory shear measurements can be done with the parallel-disk arrangement in a manner similar to the case of the cone-n-plate viscometer and, similarly, the material fimcdons i), G, C, and others can be generated. However, a slightly different tedinique [36] is at times used wherein the polymer melt sample is deformed between two oscillating parallel eccentric disks as shown in Fig. 3.2. In this case, too, it has been shown that the fluid elements undergo a periodic sinusoidal deformation and the forces exerted on the disk are thus interpreted in terms of G and G" [4]. 

The cone-n-plate viscometer is a widely used instrument for measurement of shear flow rheological properties of polymer melts [9-20]. The principal features of this viscometer are shown schematically in Fig. 3.1. The sanaple, whose rheological properties are to be measured, is trapped between the circular conical disk at the bottom and the circular horizontal plate at the top. The cone is connected to the drive motor which rotates the disk at various constant speeds, whereas the plate is connected to the torque-measuring device in order to evaluate the resistance of the sample to the motion. The cone is truncated at the top. The gap between the cone and plate is adjusted in such a way as to represent the distance that would have been available if the untruncated cone had just touched the plate. The angle of the cone surface is normally very small (0o 4° or 0.0696 radians) so as to maintain [4] cosec Op = 1. The cone angles are chosen such that for any point on the cone surface, the ratio of angular speed and distance to the plate is constant. This ensures that the shear rate is constant from the cone tip to the outer radius of the conical disk. Similarly, the shear... 

Figure 9. a) Flow curve using a cone and plate viscometer for a water-isopropyl myristate-water emulsion as a function of dose of gamma-irradiation sho n in Mrad. b)Viscosity of a w/o/w emulsion at shear rate of 1650 s stabilized with Pluronic surfactants (5 F85/5i F88) in the external phase as a function of radiation dose. The increase in viscosity shown by the flow curves indicates structure build-up in the external phase. The hysteresis loop exhibited by the gelled sample indicates that the structure of the external gel phase is broken down during shearing. Reproduced with permission from Ref. Hi. Copyright 1982, J. Pharm. Pharmacol. 

Figure 3.1 Schematic diagram showing the principal features of a cone-n-plate rotational viscometer.

For thermoplastic melt studies, rotational viscometers with either the cone-n-plate or parallel-disk configuration are used. 

The viscosity of emulsions obtained from two mutually incompatible polymers dissolved in a common solvent was studied by a falling ball viscometer, a cone-plate viscometer, and a capillary viscometer. The two polymers are polyacrylonitrile and polyurethane, and the solvent is N-methyl-pyrrolidone. The measurements are compared with theory, and a model is proposed for the development of a stationary pressure flow of an emulsion in a capillary. 

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