Viscometers, viscometry

Viscosity measurements began to be used by colloid chemists when Thomas Graham investigated the peptisation of silicic acid in the 1860 s. Soon, with the introduction of the Ostwald U-tube viscometer, viscometry became one of the most widely used methods of investigating colloidal solutions—and to a large extent it still is used for this purpose. 

Slurry Viscosity. Viscosities of magnesium hydroxide slurries are determined by the Brookfield Viscometer in which viscosity is measured using various combinations of spindles and spindle speeds, or other common methods of viscometry. Viscosity decreases with increasing rate of shear. Fluids, such as magnesium hydroxide slurry, that exhibit this type of rheological behavior are termed pseudoplastic. The viscosities obtained can be correlated with product or process parameters. Details of viscosity deterrnination for slurries are well covered in the Hterature (85,86). 

Dilute Solution Viscometry - The hydrogenated and hydroformyl ated (10%) PBD were completely soluble in toluene. Intrinsic viscosity measurements were carried out in toluene at 30°C using a Cannon-Ubbelohde viscometer. 

The viscosities of products in solution (0.5 Weight %/volume) were measured by dilute solution viscometry using a Cannon Ubellohde viscometer at 35 °C. 

The viscosity is measured with the help of a viscometer and the method is known as viscometry. Molecular weight Determination by Viscometry... 

For Molecular weight determination by viscometry we do not need absolute h value, viscosity measurements may be carried out in simple Ostwald Viscometer. Because of (the non-Newtonian behaviour of most macromolecular solutions at high velocity gradients in the capillary, the viscometer dimensions are chosen in such a manner that the viscosity gradient is the smallest possible. 

The laboratory technique for measuring viscosity is called viscometry (sometimes viscosimetry), and the device in the laboratory used to measure viscosity is called a viscometer (sometimes viscosimeter). 

Define rheology, shear force, shear stress, shear rate, Newtonian fluid, dynamic viscosity, centi-poise, kinematic viscosity, centistokes, viscometry, and viscometer. 

Viscometry. Intrinsic viscosity. Kinematic viscosities (v=rj/p, where tj is the viscosity) were measured in a Cannon-Ubbelohde capillary viscometer. At least four concentrations, covering the relative viscosity range where the subscript s denotes the solvent) from about 1.8 to 1.2 were used to construct Schul -Blaschke plots. These plots of versus where... 

Viscometry. Viscosities of aqueous polymer solutions were measured using a Cannon-Fenske 50 viscometer immersed in a 20°C water bath. The limiting viscosity number was determined from 5 viscosity measurements using the Huggins equation (9). The limiting viscosity number of aged poly( 1-amidoethylene) in 0.01 M aqueous Na2SC>4 was 2.45 dL/g. 

A rather complete survey of the entire field of viscometry, including the mathematical relationships applicable to various types of instruments, has been made by Philippoff (P4). The problem of slip at the walls of rotational viscometers has been discussed by Mooney (M15) and Reiner (R4). Mori and Ototake (M17) presented the equations for calculation of the physical constants of Bingham-plastic materials from the relationship between an applied force and the rate of elongation of a rod of such a fluid. ... 

Viscometry measurements were made in benzene at 30 °C and in TFE at 50 °C with uncalibrated Cannon-Ubbelohde dilution viscometers which gave solvent times greater than 100 seconds. The viscometers used had centistoke ranges denoted by viscometer sizes of 50 and 75 for benzene and TFE, respectively. Stock solutions were made up on gram solute/100 gram solution basis and converted to gram/deciliter via the solvent density at the temperature of measurement. The solvent densities used were d ene = 0.8686 (11a) and dlra = 1.3429 obtained from pycno-metric measurements (12). The density—temperature relationship for TFE obtained from regression analysis of the experimental pycnometric data is... 

This protocol describes a method for measuring the viscosity of pure liquids and solutions by capillary viscometry. The sample is loaded into a Cannon-Fenske viscometer. The time required for the sample to flow between two time points on the viscometer is used to calculate the kinematic viscosity or viscosity. 

Physical Measurements. Intrinsic Viscosities. Intrinsic viscosities were obtained using dilute solution viscometry (Cannon-Ubbelohde viscometers). 

Physical Measurements. Molecular Weight. Intrinsic viscosities were determined using dilute solution viscometry (Cannon-Ubbelohde viscometers). For the poly (methyl methacrylate) polymer the following empirical expressions were used to obtain molecular weights (4) ... 

Viscometry The specific viscosity of each polymer from the bulk polymerization was measured in acetone at 30°C using an Ubbelohde dilution viscometer. Five concentrations in the range of 1.120 to 0.242 g/d poly(vinyl acetate) and polyvinyl trideuteroacetate) and 0.385 to 0.084 g/dl (poly(trideu-terovinyl acetate)) were run. Intrinsic viscosity was calculated by extrapolation of the Tlsp/c versus c plot to zero concentration. Number average molecular weights were calculated using the equation(20) [q] =1,0 x 10 1 [Mn] 0 72 which is in the mid range of the equations listed. 

Viscosity Measurements, Previous studies (2) have shown that dilute solutions of Pluronic F127 exhibit Newtonian flow characteristics and consequently, it is permissible that the viscosity of these solutions is measured by capillary viscometry. A suspended-level viscometer was used and solutions were thermostatted to within... 

Equation (4.4) is an unwitting statement that the velocity (l/t) of a sol s planar flow is inversely proportional to t. A capillary viscometer is designed to maintain r, l, V, and t (1 atm) constant, so that ti, is direcdy proportional to tt. The generalized equation for a single measurement (single-point viscometry) is... 

Measurements taken from a series of different ct arrived at in situ by dilution in specially designed viscometers comprise the capillary viscometry technique known as dilution viscometry. Neither single-point nor dilution viscometry is suitable for suspensions, because of the unreliability of their , resulting from heterogeneities of particle size, shape, and interaction. Variations in t- are conducive to slippage, wall effects, and turbulence. 

In viscometry, it is usually necessary to correct for end effects (e.g., entrance and exit effects in axial flow instruments) and for slip between sample and viscometer surfaces. 

The application of refractive index and differential viscometer detection in SEC has been discussed by a number of authors [66-68]. Lew et al. presented the quantitative analysis of polyolefins by high-temperature SEC and dual refractive index-viscosity detection [69]. They applied a systematic approach for multidetector operation, assessed the effect of branching on the SEC calibration curve, and used a signal averaging procedure to better define intrinsic viscosity as a function of retention volume. The combination of SEC with refractive index, UV, and viscosity detectors was used to determine molar mass and functionality of polytetrahydrofuran simultaneously [70]. Long chain branching in EPDM copolymers by SEC-viscometry was analyzed by Chiantore et al. [71]. 

Due to the problems encountered with SEC-LALLS and SEC-viscometry, a triple-detector SEC technology has been developed, where three on-line detectors are used together in a single SEC system. In addition to the concentration detector, an on-line viscometer and a LALLS instrument are coupled to the SEC... 

Intrinsic Viscosity. Dilute-solution viscometry of samples in toluene was carried out in a Cannon-Ubbelohde semimicrodilution viscometer (size 25) in a temperature-controlled bath (25.0 0.2 °C). At least three concentrations were measured, and the results were extrapolated to infinite dilution by using the Huggins and Kramers relations... 

Flow through a porous cell has been used in the viscometry of mobile liquids. The older types of viscometer used in testing lubricating oils, such as those of Redwood, 3 Engler, etc., in which a liquid flows through a small hole in the bottom of a vessel, have no scientific interest, and are being replaced by instruments of the type described above. 

Viscometry has become such a routine technique in many laboratories that it seems unnecessary to mention the usual precautions such as the clarification of sample, the cleanliness of the viscometer, the temperature control (to 0.01°C or better), the timing device, the vertical alignment of capillary viscometer, etc. In this section we will only describe the basic equations used in the viscosity measurements and various corrections and precautions which are necessary to insure reliable results. (For a monograph, see, for example, Barr, 1931.)... 

Another valuable technique for study of the physical form of the active centres is viscometry. It is reasonably simple to add a vacuum viscometer to the sealed polymerization vessel and to measure the viscosity of the solution after polymerization is complete but while active centres still exist [31]. These values can be compared with the viscosity after destruction of the centres by traces of alcohol. As the solution viscosity is sensitive to the apparent total molecular weight of the polymer any association of polymer molecules via their active ends will be readily apparent. This technique was used [32] in very early experiments to show that in hydrocarbon solvents extensive association of polymer chains often occurs and has an important effect on the polymerization kinetics. Light scattering techniques can be employed in a similar manner [33] enabling the apparent molecular weight to be directly determined. 

The opportunity to measure the dilute polymer solution viscosity in GPC came with the continuous capillary-type viscometers (single capillary or differential multicapillary detectors) coupled to the traditional chromatographic system before or after a concentration detector in series (see the entry Viscometric Detection in GPC-SEC). Because liquid continuously flows through the capillary tube, the detected pressure drop across the capillary provides the measure for the fluid viscosity according to the Poiseuille s equation for laminar flow of incompressible liquids [1], Most commercial on-line viscometers provide either relative or specific viscosities measured continuously across the entire polymer peak. These measurements produce a viscometry elution profile (chromatogram). Combined with a concentration-detector chromatogram (the concentration versus retention volume elution curve), this profile allows one to calculate the instantaneous intrinsic viscosity [17] of a polymer solution at each data point i (time slice) of a polymer distribution. Thus, if the differential refractometer is used as a concentration detector, then for each sample slice i. 

The single-capillary viscometer (SCV) is represented in Fig. la. Its design is a direct extrapolation of classical viscometry measurement. It is composed of a small capillary, through which the solvent flows at a constant flow rate, and a differential pressure transducer (DPT), which measures the pressure drop across the capillary. SCV obeys PoiseuiUe s law and the pressure drop AP across the capillary depends on the geometry of the capillary, on flow rate Q, and on viscosity of the fluid 7j according to... 

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