System viscosity

Once the value of the constant and the a value in Eq. (2.36) have been evaluated for a particular system, viscosity measurements constitute a relatively easy method for determining the molecular weight of a polymer. Criticize or defend the following proposition Since viscosity is so highly dependent on molecular weight for M > M, a 10% error in 17 will result in a 34% error in M above M, but only a 10% error in M below M, . 

To maintain a high polymerization rate at high conversions, reduce the residual amount of the monomer, and eliminate the adverse process of polyacrylamide structurization, polymerization is carried out in the adiabatic mode. An increase in temperature in the reaction mixture due to the heat evolved in the process of polymerization is conductive to a reduction of the system viscosity even though the polymer concentration in it rises. In this case, the increase in flexibility and mobility of macromolecules shifts the start of the oncoming gel effect into the range of deep transformation or eliminates it completely. 

Finishing of the filler surfaces may also greatly affect the system viscosity. For mica-filled PP [31] and various thermoplastics filled with calcium carbonate [202, 261] it was shown that the relative viscosity of filled systems was lower than that of systems which contained equivalent quantitied of unfinished filler. Note that in contrast to viscosity in shear, the viscosity in stretching is higher for systems with treated filler [202]. 

Photosensitization of diaryliodonium salts by anthracene occurs by a photoredox reaction in which an electron is transferred from an excited singlet or triplet state of the anthracene to the diaryliodonium initiator.13"15,17 The lifetimes of the anthracene singlet and triplet states are on the order of nanoseconds and microseconds respectively, and the bimolecular electron transfer reactions between the anthracene and the initiator are limited by the rate of diffusion of reactants, which in turn depends upon the system viscosity. In this contribution, we have studied the effects of viscosity on the rate of the photosensitization reaction of diaryliodonium salts by anthracene. Using steady-state fluorescence spectroscopy, we have characterized the photosensitization rate in propanol/glycerol solutions of varying viscosities. The results were analyzed using numerical solutions of the photophysical kinetic equations in conjunction with the mathematical relationships provided by the Smoluchowski16 theory for the rate constants of the diffusion-controlled bimolecular reactions. 

The experimental and simulation results presented here indicate that the system viscosity has an important effect on the overall rate of the photosensitization of diary liodonium salts by anthracene. These studies reveal that as the viscosity of the solvent is increased from 1 to 1000 cP, the overall rate of the photosensitization reaction decreases by an order of magnitude. This decrease in reaction rate is qualitatively explained using the Smoluchowski-Stokes-Einstein model for the rate constants of the bimolecular, diffusion-controlled elementary reactions in the numerical solution of the kinetic photophysical equations. A more quantitative fit between the experimental data and the simulation results was obtained by scaling the bimolecular rate constants by rj"07 rather than the rf1 as suggested by the Smoluchowski-Stokes-Einstein analysis. These simulation results provide a semi-empirical correlation which may be used to estimate the effective photosensitization rate constant for viscosities ranging from 1 to 1000 cP. 

An interesting problem arises when we consider solutions or colloidal sols where the diffusing component is much larger in size than the solute molecules. In dilute systems Equation (1.14) would give an adequate value of the Peclet number but not so when the system becomes concentrated, i.e. the system itself becomes a condensed phase. The interactions between the diffusing component slow the motion and, as we shall see in detail in Chapter 3, increase the viscosity. The appropriate dimensionless group should use the system viscosity and not that of the medium and now becomes... 

While conductivities of nanocarbons dispersed in polymers fall short of those of metals, a variety of applications can be unlocked by turning an insulating matrix into a conductor, which requires only small volume fractions that can therefore keep the system viscosity at a level compatible with composite processing techniques. Of particular interest are novel functionalities of these conductive matrices that exploit the presence of a conductive network in them, such as structural health monitoring (SHM) based on changes in electrical resistance of the nanocarbon network as it is mechanically deformed [30]. 

Skeggs innovative step, the introduction of air bubbles into the flowing stream, attempted to minimize the time taken for a steady-state condition to be reached in the detector. The definitive description of dispersion in segmented streams (Snyder [37]) showed a complex relationship between internal diameter, liquid flow rate, segmentation frequency, residence time in the flow system, viscosity of the hquid and surface tension. 

Figure I 1.6. Master viscosity curve produced by superposing all data for all systems. Viscosity data taken at 175 °C have been shifted to 150°C by employing the temperature scaling factor aT for pure polystyrene. The master viscosity curve is identical to the viscosity curve for pure polystyrene at 1 atm and 150 °C, which is displayed as the solid line. Data from Kwag (1998).

The effect of physical properties on column efficiency can be roughly estimated from Fig. 8.16. For this system, viscosity is 0.35 cP (see statement of previous example) and relative volatility is 3.6, so the abscissa is 1.26. The ordinate, or column efficiency, is read to be 68 percent. 

According to Cardenas and O Driscoll [39], there exist two populations of macroradicals, of a polymerization degree greater and smaller than a certain critical size Pc. Pc is defined by a bend in the plot of log tj (system viscosity) vs. log DP (degree of polymerization of the dissolved polymer). With increasing concentration and chain length of the polymer, the importance of poly-... 

Viscosity (dynamic) the viscosity of a solution of polyvinyl acetate phthalate methanol (1 1) is 5000 mPas. In metha-nol/dichloromethane systems, viscosity increases as the concentration of methanol in the system increases. 

Viscosity is an important property of residual fuel oils because it provides information on the ease (or otherwise) with which a fuel can be transferred, under the prevaihng temperature and pressure conditions, from storage tank to burner system. Viscosity data also indicate the degree to which a fuel oil must be preheated to obtain the correct atomizing temperature for efficient combustion. Most residual fuel oils function best when the burner input viscosity lies within a certain specified range. 

Size-exclusion chromatography (SEC) has become the technique of choice in measuring the molar-mass distributions of polymers that are soluble in easily handled solvents (Dawkins, 1989). The technique as widely practised is not an absolute method and a typical SEC system must be calibrated using chemically identical polymers of known molar mass with a narrow distribution unless a combined detector system (viscosity, light scattering and refractive index) is employed. 

The monomers were charged into the autoclave, and trace amounts of oxygen purged by the freeze-thaw technique. Irradiation was carried out with gamma rays from a (50Co source at various temperatures. CHC13, CH2C12, dimethylformamide (DMF), triethylamime (TEA), and p-benzoquinone were used as additives in the polymerization systems. Viscosity of the copolymers obtained was measured in Freon 113 at 35°C. Infrared spectra and x-ray diffraction patterns of the sample were also obtained. NMR measurements of (proton and fluorine) were also done. 

It is possible that such inconsistencies reflect different interfacial interactions between plastics and cellulosic tiller. For example, loading of 50% (w/w) of wood flour to two different polyethylenes can increase the system viscosity 100-fold or only 25-fold. In the first case polyethylene was metallocene PE (MFI 4 g/10 min, MWD =... 

In SI units is measured in newtons per square meter and p in kilograms per meter-second or pascal-second. In the cgs system viscosity is expressed in grams per centimeter-second, and this unit is called the poise (P). Viscosity data are generally reported in centipoises (cP = 0.01 P = 1 mPa-s), since most fluids have viscosities much less than 1 P. 

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