High-shear-rate viscosity

Since the thermal diffusivity is much less sensitive to molecular weight distribution than the viscosity, it is the high shear rate viscosity that is the governing property. 

Measurement of high-shear-rate viscosity of lubricants has advanced tremendously in recent years and is now relatively routine. High-pressure capillary and rotational viscometers are both commercially available, and both CEC and ASTM have defined standardized test methods for their use (CEC L-36-A-87, ASTM D 4683 and ASTM D 4741 for the rotational and ASTM D 4624 for the capillary). 

Alexander, D.L. (1989) Change of high-shear rate viscosity of engine oils during use A review, in high-temperature high-shear (HTHS) oil viscosity Measurement and relationship to engine operation. ASTMSTP 1068, 60-73. 

SAE viscosity grade Low-temperature,°C, cranking viscosity, mPa-s, maximum Low-temperature,°C, pumping viscosity, mPa-s, maximum, with no yield stress Low-shear rate kinematic viscosity mm /s at 100°C maximum/minimum High-shear rate viscosity, mPa-s at 150°C, minimum... 

A6/B6 for use at extended drain intervals in high-performance petrol and diesel light vehicle engines designed for low-friction, low-viscosity lubricants with a high-temperature/high-shear rate viscosity of 2.9-3.5 mPa.s. 

Table IV. High Shear Rate Viscosity Characteristics0...

Figure 10. High shear rate viscosity characteristics of formulations I, II, and III from Table II (Serves extrusion rheometer)...

Figure 13. Pressure dependence of the rheological parameters from the Herschel-Bulkley model (n, K, r0, and a high shear rate viscosity tjhb) for a weighted water-based drilling fluid at 40 °C. (Reproduced with permission from reference 72. Copyright 1988 Society of Petroleum Engineers.)...

Hughes et al. (32) have attempted to explain the rheology of CMC-bentonite drilling fluids by relating the high shear rate viscosity to the polymer concentration cP and the intrinsic viscosity ([17]), which is a polymer size (or molecular weight) parameter. Hughes et al. found... 

The high shear rate viscosity rjp shows less variation with pH or I (Figure 20). Heath and Tadros (75) attempted to explain the increase in r0 with increasing I and pH — 71 by the flocculation of bentonite clay and the formation of house-of-cards types of structures caused by edge-to-face attractive interactions (see reference 77 for a detailed discussion of flocculation and the formation of edge-to-edge and edge-to-face structures). 

Casson high shear rate viscosity (Pa s) consistency of power law fluid (Pa - sn) constant (Pa - sn) length (m) constant... 

The two associative thickeners examined in the remainder of this text whose synthesis has not been discussed are hydrophobe-modified alkali-swellable emulsions (HASE) discussed in Chapters 25, 27, and 28, and hydrophobe-modified (hydroxyethyl)cellulose (HMHEC, discussed in Chapters 17, 18, and 27). HASE thickeners, by far the lowest cost hydrophobe-modified thickeners produced, should have achieved the largest market share on the basis of cost of production, but this situation does not appear to be the case (discussed in Chapter 28) in large part because of the poor properties observed with the lowest cost latex, vinyl acetate, used to form the continuous film. The applied-film properties 46) of vinyl acetate can be substantially improved through the use of HEUR polymers. HMHEC, synthesized by a matured (30-year-old) commercial slurry process (47) has achieved commercial acceptance, in large part because of linear high shear rate viscosities achieved in blends with HEUR thickeners (Chapter 27). 

Deformable or soft particles and droplets show the same behavior as rigid particles. However, the high shear rate viscosity of deformable panicles is lower than that observed for rigid particles of the same internal phase content. 

Glass, J. E., Lundberg, D. J., Ma, Z., Karunasena, A., Brown, R. G., Viscoelasticity and High Shear Rate Viscosity in Associative Thickener Formulations, Proc. Water-Borne Higher-Solids Coat. Symp., Vol. 17, 1990, pp. 102-20. 

The optical film thickness measurements obtained for six lubricants have shown that the Hamrock and Dowson formulae can be applied with confidence in the range of operating conditions tested. However a limitation appears when the high material parameter (pressure viscosity coeffit ient reduced elastic modulus) reaches 10. In this case, the theoretical film thickness equations underestimate by 20 to 50 per cent the measured minimum films and by 5 to 20 per cent the centre films thicknesses. Further, fair agreement between theory and experiment is also obtained with the non-newtonian lubricant tested if the high shear rate viscosity value is used in Che equations instead of Che low shear rate viscosity. 

First we will look at the shear rates involved during the screen printing process. When the ink is stirred and transferred to the screen the shear rate is approximately 10" to 1 s". The shear rates near the vicinity of the squeegee edge are difficult to estimate. These estimates of shear rate are 1 to 10 g-i.iss.Do.ns practice, it is difficult to measure the high shear rate viscosity of thick-fihn inks (greater than 500 s ) because of cohesive failure of the paste. 

Eq. 8 is the power-law equation. The parameters m and n were determined from the high-shear-rate viscosity data in Fig. 3. The pressme effect on viscosity was considered in the calculation. The predicted values are shown as dashed cmves in Fig. 7. 

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