Continuous measurement, viscosity

From that point, the necessity of continuously measuring viscosity, in addition to polymer concentration, became obvious. Several attempts were made to adapt existing viscometers as GPC detectors, but the problem of internal volume was critical. Ouano [2] published the first design of a single-capillary viscometer which was based on pressure measurement. Several similar designs [3-6] were pubfished and a commercially available instrument, the Waters Model 150CV (Waters Associates, Milford, MA, U.S.A.), based on a design described in Ref. 4, became commercially available. 

We now consider a 40% silicone oil premixed emulsion dispersed in an aqueous phase. In Fig. 9 the evolution of mean diameter is plotted as a function of the applied shear rate. The dispersed phase volume fraction is kept constant at 75%, while the emulsifier concentration in the continuous medium is varied from 15 wt % to 45 wt %. The error bars show the distribution width deduced from the measured uniformity. At a given shear rate, smaller droplets with lower uniformity are produced (see Fig. 9) when surfactant concentration increases. For example at 45% of Ifralan 205 the uniformity never exceeds 15% whatever the applied shear rate, whereas it is of the order of 25% for 15% of Ifralan 205. Some microscope pictures of the emulsions obtained are given in Fig. 10. To understand the evolution, we may argue that the continuous phase viscosity increases... 

However, they may not indicate the true bulk viscosity of a suspension that forms a thin layer of the continuous phase (e.g., serum of tomato juice) around the immersed probe or when the probe is covered by a higher viscosity gel due to fouling. Vibrational viscometers are suitable for measuring viscosities of Newtonian fluids, but not the shear-dependent rheological behavior of a non-Newtonian fluid (e.g., to calculate values of the power law parameters). 

Dynatrol Viscosity Systems are designed for continuous measurement of viscosity in process streams. Dynatrol Viscosity Detectors are installed directly in process vessels without the need for sampling or analysis. Response is immediate and continuous. Utilizing this system, we carried out a series of experiments to study the change in viscosity of polymer solutions when we introduced a change in polymer chain ends. 

A special group of detectors are those which continuously measure the molar mass of sample components in the eluate. Their application allows to omit the calibration of the gel chromatographic system. So far, vapor phase osmometry for solutes with lower molar masses, and viscosity and light scattering measurements for polymers have been applied. 

The bimodal model has also been applied to polydisperse suspensions (Probstein et al. 1994), which in practice generally have particle sizes ranging from the submicrometer to hundreds of micrometers. In order to apply the bimodal model to a suspension with a continuous size distribution, a rational procedure is required for the separation of the distribution into fine and coarse fractions. Such a procedure has not been developed so that an inverse method had to be used wherein the separating size was selected which resulted in the best agreement with the measured viscosity. Again, however, the relatively small fraction of colloidal size particles was identified as the principal agent that acts independently of the rest of the system and characterizes the shear thinning nature of the suspension viscosity. 

Coran, 1978). During this test, fully mixed but unvulcanized rubber is contained in a heated cavity. Imbedded in the rubber is a rotating disc. Viscosity is continuously measured (by the torque required to keep the rotor rotating at a constant rate) as a function of time. The temperature is selected to be characteristic of rather severe processing (extrusion, calendaring, etc.). 

Continuous measurement of viscosity. The accuracy of the Mark-Houwink equation will be improved if the intrinsic viscosity of a fraction at each retention volume can be measured continuously. An automatic viscometer having a capillary of 0.5 mm in diameter and a length of 200 mm was constructed and applied to the estimation of molecular mass of di- and triblock copolymers of polystyrene-polyisoprene P(S-IP) and di-block copolymer of P(S-MMA) [32]. In the case of copolymers which have homogeneous... 

Another new method for the dynamic measurement of ki a uses gas phase dynamics and consists of continuously measuring the composition of the outlet gas in response to a step input of a nonreactive tracer such as CO2 in the inlet gas stream (Andre et al., 1981). This method is especially useful under particular conditions for application to high viscosity media and solid-substrate fermentations. 

DETA is an ideal technique for monitoring the cure of silicone potting compounds because the unreacted material (with its low viscosity) can be directly applied to the dielectric sensor and continuous measurement made as the material transforms from a low molecular weight liquid to a high molecular weight crosslinked rubber. 

There is no suitable instrument to measure plastic melt viscosity continually. However, viscosity depends on temperature. Therefore the measurement and control of temperature is substituted for the measurement and control of viscosity. This is the procedure used in automatic control. ... 

Con osition and Physical Properties Many composition measurements are obtained indirecdy. Physical properties such as temperature, viscosity, vapor pressure, electric conductivity, density, and refractive index are measured and used to infer the conposition of a stream, in place of a direct measurement. A number of other measurement techniques have become commonplace for the on-line analysis of composition. These include gas chromatography and mass and infrared spectrometry. These instruments are very accurate but are expensive and often fail to provide the continuous measurements that are required for rapid regulation. 

A new type of test methodology for characterizing engineering plastics has been developed. These techniques simulate the extrusion and molding process to show what a polymer would undergo in terms of shear, temperature, pressure, and residence-time deformation. The behavior of a compound can be accurately predicted prior to processing. An online-type rheometer continuously measures the viscosity of the polymer from the die on a real-time basis, and the data is used to make screw speed adjustment to keep the viscosity consistent (10). 

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