Comparative viscosities

Frechet [49, 89] was the first to compare viscosity parameters for (A) linear topologies, as well as (B) random hyperbranched polymers and (C) dendrimers. More recently, we reported such parameters for (D) dendrigraft polymers [111] as shown in Figure 1.19. It is clear that all three dendritic topologies behave differently than the linear. There is, however, a continuum of behavior wherein random hyperbranched polymers behave most nearly like the linear systems. Dendrigrafts exhibit intermediary behavior, whereas dendrimers show a completely different relationship as a function of molecular weight. 

The buzzword polarity, derived from the dielectric approach, is certainly the most popular word concerning solvent effects. (It is the basis for the famous rule of thumb similia similibus solventur, i.e., like dissolves like in English.) We should add like helps like. Let us compare toluene and n-hexane as solvents. At temperatures when both solvents have comparable viscosity, the reaction between 1,2,4,5-tetrafluorobenzene and its anion-radical proceeds in different ways (Werst 1993), depending on the solvent. In toluene, the reaction consists of electron exchange ... 

Table I. COMPARATIVE VISCOSITIES BETWEEN VARIOUS COLLOIDS...

Coefficient de viscosite des nitrocelluloses industrielles, called also Unit MB, was proposed in 1934 by General Goujon as a value for comparing viscosities of industrial NC s. 

Thorpe and Rodger compared viscosities at temperatures where the slope of the curve is the same (d y/d/=const.), i.e. when temperature has the same effect, on the viscosity. The ratio of viscosities measured at two temperatures of equal slope was found to be constant. They also considered the molecular viscosities, r Mv), where (Mv) is the molecular volume, and what they called the molecular viscosity work rj Mv), or the work required to move a surface equal to the molecular viscosity through the specific molecular length MvY at unit velocity. Some general results found for normal liquids were ... 

I he diagram of Fig. 9-1 is typical of mixtures of two small molecules, or of two polymers of comparable molecular weight and comparable viscosity. Polymer solutions, or blends of two polymers with very different molecular weights, have asymmetric phase diagrams, reflecting the asymmetry of the molecular sizes (see Fig. 9-2). 

The principal glass-making processes take place at various temperatures according to the type of glass, but at comparable viscosity values. During melting and refining... 

A study of the low temperature properties of several VI improver systems showed that at the high shear rate of the CCS, PMA, OCP and HSD (SBC) all had comparable viscosities. For the latter two, this results from substantial non-Newtonian character at low temperatures. Fig. 5.11 [81]. Results for polyisobutylene, PIB, adequately met the standards when extrapolated low-temperature viscosities were used. 

Viscosity measurements can be made using several different methods and attendant equipment. To help relate viscosities reported in different units, Table III reports comparative viscosities using different methods of measurement. The accuracy will lessen as non-Newtonian flow (thixotropy, pseudoplasticity, etc.) increases, but it serves as an excellent guide. 

When comparing viscosity results (either Mooney ML (l-i-4) from Table I or apparent viscosity at Y= 10 sec -1 from Table II) with mixing data given in Table IV, it can be seen that, as expected, the higher... 

Classify polymer liquid crystals in fuiKtion of their chemical shuctures. Compare viscosities of longitudinal and orthogonal polymer liquid crystals. 

The use of the Knox plots to study the causes of micellar reduced efficiencies leads to the following conclusions. The micellar phase flow anisotropy seems to be much higher than the flow anisotropy obtained with a hydro-organic phase of comparable viscosity (increased A term). This is only partly due to the micellar viscosity. The main reason of such differences in flow patterns is the partial clogging of the stationary phase pores by adsorbed surfactant molecules [19, 22]. A temperature raise decreases the mobile phase viscosity and the amount of adsorbed surfactant [22]. Both effects decrease the flow anisotropy and the A term. It will be exposed thereafter that alcohol additions to a micellar phase dramatically reduce the amount of adsorbed surfactant. 

Mooney viscosimeter n. An instrument invented by M. Mooney in 1924, used to measure the effects of time of shearing and temperature on the comparative viscosities of rubber compounds. It consists of a motor driven disk, tooth-surfaced on the sides, enclosed within a die cavity formed by two halves maintained at controlled temperature and closing force. The specimen is a double disk, joined at the edges and trapped between the die halves and the rotor (ASTM, www.astm.org). 

TABLE 1. Comparative Viscosity Data Obtained from the Usual and the Modified Huggins Equation... 

Table 10. Comparative Viscosities of Cycloaliphatic Epoxies, Epoxidized Oils, and DGEBA...

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