Relative viscosity, effect

Viscosity Index Improvers. VI improvers are long-chain, high molecular weight polymers that increase the relative viscosity of an oil at high temperatures more than at low temperatures. In cold oil the molecules of the polymer adopt a compressed coiled form so that the affect on viscosity is minimized. In hot oil the molecules swell, and interaction with the oil produces a proportionally greater thickening effect. Although the viscosity of the oil—polymer mixture decreases as the temperature increases, viscosity does not decrease as much as the oil alone would decrease. 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Rheological experiments have shown that the relative viscosity of compositions filled with the above materials is an exponential function of filler content by volume. The impact of an otherwise constant quantity of filler increases in the series FP — LDP — SDP, i.e., symbatically with the probability of particle comminution in the plasticization process. This effect is most clearly apparent for... 

For scaly fillers the increase of relative viscosity with filler concentration is not as pronounced as in case of fibrous fillers [177,178]. Owing to filler orientation, the flow curves for systems with different concentrations of a fibrous and a scaly filler may merge together at high shear rates [181]. In composites with a dispersed filler the decrease of the effective viscosity of the melt with increasing strain rate is much weaker. 

Note that, apart from the filler particle shape and size, the molecular mass of the base polymer may also have a marked effect on the viscosity of molten composites [182,183]. The higher the MM of the matrix the less apparent are the variations of relative viscosity with varying filler content. In Fig. 2, borrowed from [183], one can see that the effect of the matrix MM on the viscosity of filled systems decreases with the increasing filler activity. In the quoted reference it has also been shown that the lg r 0 — lg (MM)W relationships for filled and unfilled systems may intersect. The more branches the polymer has, the stronger is the filler effect on its viscosity. The data for filled high- (HDPE) and low-density polyethylene (LDPE) [164,182] may serve as an example the decrease of the molecular mass of LDPE causes a more rapid increase of the relative viscosity of filled systems than in case of HDPE. When the values (MM)W and (MM)W (MM) 1 are close, the increased degree of branching results in increase of the relative viscosity of filled system [184]. 

Not all suspensions will exhibit wall slip. Concentrated suspensions of finely ground coal in water have been found to exhibit wall slip [Fitzgerald (1990)]. This is to be expected because the coal suspension has a much higher apparent viscosity than the water. In contrast, when the liquid is a very viscous gum, the addition of solids may have a relatively small effect. In this case, the layer at the wall will behave only marginally differently from the material in the bulk. 

During this reaction, some caprolactam is also liberated. The reaction is largely completed within the processing time (typically 3-5 min). The increase in intrinsic viscosity of PET can be adjusted by the amount of CBC. In practice, about 0.5 wt% of CBC is typically used. CBC is commercially available under the trade-name ALLINCO (DSM, Geleen, The Netherlands). ALLINCO is one of the most effective chain extender systems available for PET [21, 22], CBC is often used in combination with PBO for an enhanced chain extension effect. Typically, the relative viscosity of PET is increased from 1.6 to 2.0 with a stoichiometric amount of CBC + PBO (ca. 1.2 wt%) in a single-screw extruder at 300 °C. 

Figure 4.8 Effect of increasing the powder concentration in a slurry on relative viscosity. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John WUey Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Figure 4.21 Effect of axial ratio and particle concentration on relative viscosity. Data are for tobacco mosaic virus particles. Adapted from M. A. Lauffer, 7. Am. Chem. Soc., 66, 1188. Copyright 1944 by The American Chemical Society, Inc.

Using silicon nitride powder in a polypropylene/microcrystalline wax/stearic acid binder formulation, the effect of filler volume fraction (V) (over the range 50 to 70%) on relative viscosity (rjj.) was predicted from Eq. 5 ... 

Variations in the temperature coefficient of viscosity with solvent, which have also been presented as evidence of association in concentrated solutions (135,143), could be similarly related to differences in Ta among the solutions. When free draining behavior is a possibility, the relative viscosities in different solvents should be compared at the same value of Co f°r the mixtures (that is, at constant free volume rather than at constant temperature). In any case, it is clear that a very well planned series of experiments is necessary in order to test for the existence of additional specific effects such as association. These comments are not meant to suggest that association can not occur at moderate concentrations. Indeed, the existence of association in various forms of polymethyl methacrylate seems well established (144). The purpose is rather to advocate that less specific causes be eliminated before association is inferred from viscosity measurements alone. 

Figure 1. Effects of the concentration of dextrans with various molecular weights on three indices of BBC aggregation (16). MAI indicates the average number of RBCs in each aggregation unit counted under the microscope. ESR is the maximum rate of sedimentation of erythrocytes in a calibrated tube, with corrections made for changes in viscosity and density of the suspending medium following the addition of dextrans. The relative viscosity (t)r) is the ratio of the viscosity of RBC suspension to that of the suspending medium at a shear rate fo 0.1 sec 1. The RBC concentration of the suspension was 1% for MAI and 45% for ESR and r)r measurements. The vertical bars represent SEM. (A), Dx 40 (O), Dx 80 (M), Dx 150 (A), Dx 500 ( ), Dx 2000.

In the concentration range regarding the ED processes, the effective diffusion coefficient (Z>B) can be predicted via the Gordon relationship (Reid et al, 1987), which accounts for the partial derivative of the natural logarithm of the mean molal activity coefficient (y+) with respect to molality (m) and solvent relative viscosity (rjr) ... 

The sedimentation methods are normally used to measure the size of particles in a liquid medium because of the relatively high viscosity effects in liquids compared to gases. The particles in a liquid may become solvated, yielding increased weight and volume of the particle. Meanwhile, the buoyant effect on the solvated particle in the surrounding medium... 

It is worth noting that the method used by Vergnes et al. in experimentally obtaining the relative viscosity equation parameters, a and ft in Eq. 10.3-6. They worked with two almost identical PP homopolymers, one in 4-mm mean pellet diameter form, and the other in the form of small, 750-pm-diameter beads (Solvay Eltex HL 101). A 21-mm Co-TSE was fitted with a rheometric slit of length L = 52 mm, width w = 28 mm, and an adjustable gap spacing 1.5 < h < 2.5 mm. The polypropylene in pellet form was fed at the feed throat and melted. Just before the die, a second feed port introduced the PP in bead form at various rates, resulting in different effective values. Two pressure transducers at the die were used to record the slit pressure drop AP(relative viscosity was then expressed as... 

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