Viscosity of a liquid

The viscosity of a liquid increases with pressure. This behavior is relatively small for liquids of high molecular weight and low compressibility the effect can be estimated by Kouzel s method (1965) ... 

Solvent power characterizes the miscibility of solute and solvent. This concept covers two types of uses dissolving a solid or reducing the viscosity of a liquid. The solvent power should be as high as possible. However, a solvent used as an extractant should also be selective, i.e., extract certain substances preferentially from the feed being treated. 

In the last three chapters we have examined the mechanical properties of bulk polymers. Although the structure of individual molecules has not been our primary concern, we have sought to understand the influence of molecular properties on the mechanical behavior of polymeric materials. We have seen, for example, how the viscosity of a liquid polymer depends on the substituents along the chain backbone, how the elasticity depends on crosslinking, and how the crystallinity depends on the stereoregularity of the polymer. In the preceding chapters we took the existence of these polymers for granted and focused attention on their bulk behavior. In the next three chapters these priorities are reversed Our main concern is some of the reactions which produce polymers and the structures of the products formed. 

Viscosity is one of the most important properties of hydraulic fluids. It is a measure of a fluid s resistance to flow. A liquid such as gasoline which flows easily has a low viscosity, and a liquid such as tar which flows slowly has a high viscosity. The viscosity of a liquid is affected by changes in temperature and pressure. As the temperature of liquid increases, its viscosity decreases. That is, a liquid flows more easily when it is hot than when it is cold. The viscosity of a liquid will increase as the pressure on the liquid increases. 

Viscosity is normally determined by measuring the time required for a fixed volume of a fluid, at a given temperature, to flow through a calibrated orifice or capillary tube. The instmments used to measure the viscosity of a liquid are known as viscosimeters. 

In 1906, Einstein worked out a theory of the viscosity of a liquid which contains, in suspension, spherical particles which are large compared with the size of molecules of the liquid. The predictions of the theory are found to be in good agreement with the measured values of the viscosity of liquids containing colloidal particles in suspension. The presence of these obstacles increases the apparent viscosity of the liquid, and Einstein found1 that the increment is proportional to the total volume v of the foreign particles in unit volume, that is to say, the sum of the volumes of the particles that are present in unit volume of the liquid thus,... 

The greater the viscosity of a liquid, the more slowly it flows. Viscosity usually decreases with increasing temperature. Surface tension arises from the imbalance of intermolecular forces at the surface of a liquid. Capillary action arises from the imbalance of adhesive and cohesive forces. 

The viscosity of a liquid is dependent on pressure as well as temperature, but the effect is not significant except at very high pressures. A rise in pressure of 300 bar is roughly equivalent to a decrease in temperature of 1°C. 

A plot of Tvs. G yields a rheogram or a flow curve. Flow curves are usually plotted on a log-log scale to include the many decades of shear rate and the measured shear stress or viscosity. The higher the viscosity of a liquid, the greater the shearing stress required to produce a certain rate of shear. Dividing the shear stress by the shear rate at each point results in a viscosity curve (or a viscosity profile), which describes the relationship between the viscosity and shear rate. The... 

The viscosity of a liquid can also be determined by measuring the torque needed to rotate a cylinder in the liquid. Brookfield viscometers and rheometers fall into this class of instrument (Fig. 3.7). The viscometer measures the torque produced when a spindle is rotated at constant velocity in a liquid. The Rheometer produces a constant torque... 

The correlation derived by Dombrowski and Johns covers a large range of liquid viscosity and agrees favorably with experimental results. Crapper et al.[236] further applied second order and large amplitude theories to achieve better predictions. In addition, the effects of surface tension, and viscosity of a liquid sheet as well as the radial spreading and the resultant changes in the sheet thickness on the stability have been examined by Weihs.[257]... 

Highly viscous solvents, like molasses or glycerin, will have a lower diffusivity than solvents like kerosene or alcohol, all other factors being equal. This is also where temperature becomes important, because the viscosity of a liquid is highly dependent on temperature. 

A large number of empirical modifications to this expression have been proposed which model the viscosity of a liquid containing moderate concentrations of spherical particles [5] These include Mooney [6], Maron-Pierce [7] and Krieger-Dougherty [8] expressions which take into account the maximum packing fraction of the particles, and where interaction effects are absent, and can be represented by the general form ... 

Brings down the viscosity of a liquid polymer. Also, lowers the melt viscosity of a thermoplastic polymer. Thus it improves the workability and enhances the loading capability of a polymer with explosives, fillers or oxidizers. This is of special interest in the field of explosives or propellants where the amount of an explosive or oxidizer ingredient considerably increases leading to improvement in their performance. 

Equation (9) is an important result since it describes the relationship among Rs, v, r/, and Ap, the density difference. Any one of these quantities may be evaluated by Equation (9) when the other three are known. Thus, Equation (9) can be used to determine the density difference between two phases or to determine the viscosity of a liquid. In this chapter, however, our interest is in the characterization of colloidal particles by means of observations of their sedimentation behavior. Therefore, we are primarily concerned with Equations (11) and (12), which are specifically directed toward this objective. 

Equation (20), known as the Poiseuille equation, provides the basis for the most common technique for measuring the viscosity of a liquid or a dilute colloidal system, namely, the capillary viscometer. 

The viscosity of a liquid is related directly to the type and size of the molecules which make up the liquid. The variation of liquid viscosity with molecular structure is not known with exactness however, the viscosities of liquids which are members of a homologous series are known to vary in a regular manner, as do most other physical properties. For example, pure paraffin hydrocarbons exhibit a regular increase in viscosity as the size and complexity of the hydrocarbon molecules increase. 

Kinematic Viscosity—The absolute viscosity of a liquid (in centipoises) divided by its specific gravity at the temperature at which the viscosity is measured. 

We can understand intuitively how the viscosity of a liquid arises from the forces between its molecules strong intermolecular forces hold molecules together and do not let them move past one another easily. 

The viscosity of a liquid usually increases with increasing pressure. In the pressure range up to 200 bars this variation is practically linear. 

With the viscosity of a liquid we mean the resistance to flow of that particular liquid. This resistance is caused by internal friction and other interactions between the particles. Among other things, viscosity is dependent on temperature, the solid volume fraction and the properties of the particles. The viscosity of normal liquids, solutions and lyophobic colloids which are not too concentrated and contain symmetrical particles is measured by allowing a certain volume to flow through a capillary and measuring the time required by the liquid to flow through it. In figure 5.10 you can see the instrument which is used for this measurement the Ostwald viscometer. 

With the viscosity of a liquid mass we mean the flow behaviour and this depends on a) the viscosity of the dispersion medium, b) the concentration of the solid, c) the shape and dimensions of the particles and d) the interaction between the solid particles themselves and the solid particles and the molecules of the dispersion medium. 

This technique is by far the easiest for the characterization of polymers in solution. This can be seen from the simplicity of the typical (glass) viscometer shown in Figure 2.7. It is used to obtain the viscosity of a liquid by the use of Poiseuille s equation, which is... 

The viscosity of a liquid is a measure of the internal resistance offered to the relative motion of different parts of the liquid. Viscosity is described as Newtonian when the shearing force per unit area relative motion is proportional to the velocity gradient D between the planes - i.e. 

Viscosifying agent — A substance used to increase the viscosity of a liquid, mainly by swelling. 

The viscosity of a gas increases with temperature due to increased kinetic interaction between molecules, which in turn causes increased viscous drag . The viscosity of a liquid decreases with temperature due to increased thermal energy, decreasing the activated barrier for one atom to slip around its neighbors, or perhaps equivalently, the increased thermal en-... 

There are also several reactive diluents that do not contain epoxy groups. These are represented by triphenyl phosphite and y-butyrolactone (Fig. 6.7). The phosphite is a low-viscosity colorless liquid, which is sensitive to moisture. It reacts with hydroxyl groups in the resin. The y-butyrolactone is a very effective viscosity reducer. It can reduce the viscosity of a liquid DGEBA from about 15,000 to 2000 cP with only 10 pph. In the curing reaction with amines (Fig. 6.8), the lactone forms an amide, which can then crosslink with the polymer via the hydroxyl groups. 

Viscosity of a liquid is defined as the ratio between shear stress, ash, and shear rate, dy /df, so that a simple measurement of can be determined by measurement the shear stress and shear rate. 

Related Calculations. Use this procedure for a regenerative-type pump handling any liquid—water, oil, kerosene, gasoline, etc. A decrease in the viscosity of a liquid—as compared with the viscosity of water—will produce the opposite effect from that of increased viscosity. 

A relatively simple procedure for estimating the viscosity of a liquid is to assume the equation presented earlier for gases under pressure. However, when applying the Jossi et al. equation... 

An attempt to calculate the viscosity of a liquid on the basis of the classical kinetic theory led to the formula rj=Pal2c, where P=internal pressure, or=molecular diameter, and c=molecular velocity, and this was confirmed for liquid hydrogen (when molecular rotation is included), P being taken as afrom the van der Waals equation. 

Herzog connected the viscosity of a liquid with the diffusion coefficient D calculated by Einstein s equation by the relation ... 

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