Viscometry rotational

The resulting reaction mixture (8.0 ml) was transferred into the Teflon cup reservoir of a Brookfield LVDV-II+PRO digital rotational viseometer (Brookfield Engineering Labs., Inc., Middleboro, MA, U.S.A.). The reeording of viscometer output parameters started 2 min after the experiment onset. The ehanges of the dynamic viscosity (q) values of the reaction ntixture were measured at 25.0 0.1°C in 3 min intervals for up to 5 hr. The viseometer Teflon spindle rotated at 180 rpm that is at a shear rate of 237.6 s.  

In a research and development laboratory at the Dow Chemical Company in Midland, Michigan, rotational viscometry experiments on various dilutions of a test fluid, such as corn syrup, can generate the required data. Once various challenges are overcome, such as obtaining a uniform and constant temperature throughout the fluid and dealing with unusual physical behaviors of the test fluid, accurate viscosity measurements can be made and the project to optimize mixing performance can move forward. 

Amy Betz of the Dow Chemical Company collects viscosity data on a nonhazardous sample. 

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The amount of sample needed will depend on the rheometer and test fixture that are used. Ideally, there should not be excess sample (e.g., below or above the inner cylinder or outside the upper plate). Usually, sample below or above the inner cylinder does not contribute significantly to the results because of its smaller contact area compared with that of the wall of the cylinder. For steady rotational viscometry, it is often critical to cut the sample outside the upper plate. Thus it is also recommended to do so in dynamic tests. Changes in sample volume that often occur during gelation must also be considered. 

A different experimental design, called rotational viscometry, exploits the principle of fluid resistance, whereby concentrated dispersions and suspensions at and above c are sheared between two surfaces moving with different velocities relative to each other at constant or variable t. Time dependence is measurable by rotational viscometry but not by capillary viscometry. 

Arias C, Rueda C. Comparative study of lipid systems from various sources by rotational viscometry and potentiometry. Drug Dev Ind Pharm 1992 18 1773-1786. 

It is necessary to note that in performing HA rheology, also the material of the rheometer (of the parts in contact with the HA solution) is of importance. Indeed, high molar mass HA samples easily degrade in the presence of metals in a solid state or in a form of dissolved cations. Recently, Stankovska et al. [281] have applied the method of rotational viscometry for HA degradation studies. Authors strongly recommend the use of an inert material, as Teflon or similar, for the parts of the rheometer in contact with the HA solution. 

A rotating body immersed in a liquid experiences a viscous drag or retarding force, and this principle can be applied to viscometry. The chief advantage of rotational viscometry is that continuous measurements at a given shear stress or rate of shear can be made over extended periods of time. Thus time-dependent changes in flow properties can be measured conveniently. Another advantage of rotational viscometry is the ease with which shear rate can be altered. 

But though rotational viscometry seems simple in principle, in practice it turns out there are so many sources of error to consider and corrections to be made that an operating rotational viscometer of good accuracy is a rather complicated apparatus. Many commercial instruments, operating either on the continuous rotation principle or the oscillating principle, are described in the monograph by Van Wazer et al. [2]. To illustrate the application of the principles of rotational viscometry to operating instruments, we shall examine the details of two instruments the first practical rotational viscometer, devised by Couette [9], and the Per ranti-Shirley cone-and-plate viscometer. 

The analytical approach to the rotational viscometry of non-Newtonian flow as presented by Oka [4] is derived from the de Waele-Ostwald power law ... 

Figure 4-12. Viscosity vs. rate of shear for a Newtonian and a non-Newtonian liquid as measured by capillary and rotational viscometry. Data by W. Philippoff [11].

The yield stress can be obtained by the rotational viscometry technique as shown in Chapter 4. Thus from two sets of rheological determinations, one the capillary flow technique and the other rotational viscometry, enough information can be obtained to treat the problems associated with the flow of grease in pipes. 

Rotational Rheometry. Two instruments were used for these measurements. An Instron model 3250 rheometer was used for measuring rotational viscometry and forced oscillation as a function of frequency with strains in the region of 0.5. A Bohlin VOR rheometer was used for dynamic measurements at smaller strains (i.e., 0.1). 

Weissenberg effect A phenomenon sometimes encountered in rotational-viscometry studies of polymer melts and solutions at high speeds, characterized by the tendency of the polymer solution to climb the wall of the cup or the shaft of the rotor immersed in it. 

The effectiveness of antioxidant activity of 1, 4-dithioerythritol expressed as the radical scavenging capacity was studied by a rotational viscometry method [86]. L, 4-dithioerythritol widely accepted and used as an effective antioxidant in the field of enzyme and protein oxidation, is a new potential antioxidant standard exhibiting very good solubility in a variety of solvents. Fignre (8) describe effect of 1, 4-dithioerythri-tol on degradation of HA solntion nnder free radical stress [87]. 

It is also possible to employ other regimes in rotational viscometry, such as the creep regime achieved by applying a constant load, M = const. In the creep measurements, one determines the y = y(x) dependence, and in the steady-state regime, one obtains the dy/dt = /(x). It is also possible to conduct measurements at c ) = const and to observe the relaxation of stresses, that is, M = M(t) and x = x . In the latter case, there are special requirements as to the stiffness of the force-measuring device. 

The principal difference between cone-plate viscometry and rotational viscometry is in the materials that are most suitable for investigation by each method. In contrast to the... 

Expressions for other specimen geometries and higher damping are reviewed by Nielson [9]. Solid or rubbery samples are twisted as illustrated in the form of rods, tubes, strips, etc. Liquids or soft solids may be contained in one of the geometries described for rotational viscometry earher (Couette, cone-and-plate, etc.). 

Figure 16.8), where the cyclic load (stress or strain) can be applied, with the resulting strain or stress measured. For liquid samples, the geometries discussed in conjunction with rotational viscometry are often used with the drive system modified to produce sinusoidal rather than steady rotational deformation. Flexible samples such as libers, films, and rubber are preloaded in tension and oscillated about a positive tensile strain so that they do not go slack at the bottom of the sine wave. Such tests give dynamic tensile properties, E, E", etc., which are related to the corresponding shear properties by... 

The temperature dependence of the DPH anisotropy in canola oil and paraffin oil is presented as curves a and b, respectively, in Figure 7. Canola margarine was not included because it crystallized at 40°C, the matrix became opaque, and no fluorescence signal was detectable. To correlate viscosity to fluorescence anisotropy, the viscosity of the two oils and the fat were measured by rotational viscometry (Fig. 8) at temperatures above 50°C to ensure that all fat was melted. Samples were equilibrated at 50°C for 6 h prior to measurements to destroy any thermal history of the system. AU samples displayed Newtonian rheological behavior. 

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