Shear rheological instrumentation

The shear rheology instrument ISR1 (SINTECH, Berlin) is based on free damped oscillations of a ring or disk located in the interfacial layer and suspended on a tungsten torsion wire. The frequency is of the order of 0.1 Hz and can be changed at certain intervals. Details of the instrument have been given elsewhere.9... 

A rheological instrument such as a viscometer can be used to evaluate t and 7 and hence obtain a value for the shear viscosity, 17. Examples of Newtonian fluids are pure gases, mixtures of gases, pure liquids of low molecular weight, dilute solutions, and dilute emulsions. In some instances, a fluid may be Newtonian at a certain shear-rate range but deviate from Newton s law of viscosity under either very low or very high shear rates (2). 

Three different rheological measurements may be applied [36-39] (i) steady-state shear stress-shear rate measurements, using a controlled shear rate instrument ... 

Different techniques for the study of shear rheology of interfacial layers have been developed over the years however, they are mostly suited for liquid/gas inter faces. The early instruments were constructed to measure the interfacial shear viscosity under constant shear conditions. In more complex systems, nonlinear effects, shear-rate dependencies of the viscosity, and viscoelastic properties are... 

Finally Dill and Zimm have designed a new rheological instrument that can not only perform steady shear, but also measure transient responses, e.g., both stress relaxation and strain relaxation (creep recovery) experiments for dilute solutions. They have investigated the properties of T2 DNA, and studied, for example, the concentration dependence of Results are consistent with the theory of Muthukumar and Freed, and from the value of r, at infinite dilution the molecular weight of the DNA may be determined. 

Three different rheological measurements may be applied to study the bulk properties of suspension concentrates [118-120] (i) Steady state shear stress-shear rate measurements (using a controlled shear rate instrument), (ii) Constant stress (creep) measurements (carried out using a constant stress instrument), (iii) Dynamic (oscillatory) measurements (preferably carried out using a constant strain instrument). These... 

Capillary rheometers are the most widely used rheological instruments for polymer melts. They are, however, generally limited to rather high shear rates. Rotational rheometers can provide data at lower shear rates. Cone-plate and parallel disc instruments have been popular with thermoplastic melts. Pressurized instruments, such as biconical or Mooney shearing disc instruments, are used with elastomers to prevent slippage [39]. Sandwich rheometers are used at the lowest shear rates and shear stresses. 

A torsion pendulum apparatus was used to get information about the shear rheological properties of the surfactants at the interface. This sensitive instrument was not capable of detecting significant elastic or viscous properties except for Lecithine. The analysis provided data that indicated a low viscous resistance for Lecithine with an interfacial shear loss modulus of about 0.03 mN/m. Hence, we can conclude, that no network-like superstructures were formed, and that the large dilatational elastic response was mainly caused by Gibbs- and Marangoni-effects. 

The shear rheology (viscosity vs. frequency) were measured on TA instruments ARES using a parallel plate configuration from 0.1-100 rad/s at 190 °C. 

There are a number of techniques that are used to measure polymer viscosity. For extrusion processes, capillary rheometers and cone and plate rheometers are the most commonly used devices. Both devices allow the rheologist to simultaneously measure the shear rate and the shear stress so that the viscosity may he calculated. These instruments and the analysis of the data are presented in the next sections. Only the minimum necessary mathematical development will he presented. The mathematical derivations are provided in Appendix A3. A more complete development of all pertinent rheological measurement functions for these rheometers are found elsewhere [9]. 

Various methods are used to examine the viscosity characteristics of metallized gels. Two types that have received extensive application are the cone and plate viscometer and the capillary viscometer. Both instruments can measure rheological characteristics at high shear rates, and the former is useful for low shear rate measurements as well. 

A cone and plate rotational type viscometer is used to obtain rheological data in the low-to-medium shear rate range. It gives a constant rate of shear across a gap, and therefore, equations for this instrument are simple when the angle is small (less than 3°). For this reason the cone and plate viscometer has become a standard tool... 

We can distinguish between two types of stresses on an interface a shear stress and a dilatational stress. In a shear stress experiment, the interfacial area is kept constant and a shear is imposed on the interface. The resistance is characterized by a shear viscosity, similar to the Newtonian viscosity of fluids. In a dilatational stress experiment, an interface is expanded (dilated) without shear. This resistance is characterized by a dilatational viscosity. In an actual dynamic situation, the total stress is a sum of these stresses, and both these viscosities represent the total flow resistance afforded by the interface to an applied stress. There are a number of instruments to study interfacial rheology and most of them are described in Ref. [1]. The most recent instrumentation is the controlled drop tensiometer. 

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