Isothermal viscosity

Figure 6. Set ofjump discontinuities (kinks and shocks) compatible with the isothermal viscosity-capillarity model W=2.5.

Fox.T.G., Loshaek,S. Isothermal viscosity-molecular weight dependence for long chains. J. Appl. Phys. 26,1080-1082 (1955). 

The dimensionless quantity ac may be calculated as a function of v1 when data for isothermal viscosity are determined experimentally over the range of diluent concentration the lowest of the v s at which individual viscosity values were measured may be taken as the reference concentration i>. Thus it is possible to construct a plot for lflnae against 1 /(iij—v ), and if it follows a straight line, as expected from the above theory, one may determine the values of f(v, T)jBv and [/(n, T)]2/ / (T) from the intercept at — vf) = 0 and the slope of the resulting line, respectively. Since it is expected that Eq. (39) is essentially applicable only in the region quite close to the pure polymer, viscosity data pertinent to these determinations should be taken for very concentrated solutions, preferably including the pure polymer solid. 

Two parameters which will be used in later kinetic treatment of cure data are the zero-time (isothermal) viscosity, (Figure 2), and the constant K, characteristic of the rate of increase of viscosity, obtained from the linear slope of a first-order semilogarithmic cure curve plot. 

Several researchers have described changes in the isothermal viscosity behavior during the cure of thermosetting resin systems with respect to time by the following expression ... 

Fig, 15. Isothermal viscosity rise Polyether-TDI prepolymer foam (ref. 195). 

It had been shown by 1955 that the isothermal viscosity of a liquid of flexible chain molecules could be represented by the empirical relation... 

Within the framework of Eqn. (2.1) it was found by 1955 that for many homologous series ssretems the isothermal viscosity could be correlated by the relation (9,27,50,128, 200)... 

Thus, we need only compute the value of the viscosity at constant friction factor from the isothermal viscosity according to... 

The notation S x, y, z) used throughout the text means that S is being represented as a fimction of the variables x, y and z. Similarly, S (y, z) or simply denotes S taken at a constant value of the independent variable x. For example, rjj Z) denotes the dependence of the isothermal viscosity on Z. 

There is reasonably good agreement with non-isothermal viscosity data (although deviations occur at higher conversions). 

Viscosity data are usually presented in one of two forms. The first form of presentation, which is termed the isothermal viscosity, reports the viscosity at specified temperatures. The second form of presentation reports the temperature at which specified viscosities occur, e.g., the values of the Littleton softening temperature or the glass transformation temperature. In general, temperatures referring to a specified viscosity are termed isokom temperatures for that viscosity. If a series of curves showing the isokom temperatures are presented on a figure, the individual curves are termed isokoms (lines of constant viscosity). 

The identity of the alkali oxide present has a relatively small effect on the viscosity of the melt. Although the isothermal viscosity does decrease in the order Cs > Rb > K > Na > Li, the differences among the alkali oxides are small as compared to the effect of alkali oxide concentration. In fact, if low viscosity data (< 10 Pa s) are plotted against the concentration of alkali per cm of melt instead of against mol% R2O, one finds that the data for lithium, sodium, and potassium silicate melts essentially lie on the same line for any given temperature between 1100 and 1400 °C. 

The effect of water concentration on Tg and isothermal viscosity is most evident for the glass former oxides. Commercial vitreous silica is produced with water contents ranging from < 1 to > 600 wtppm of H2O. The Tg of these glasses decreases from 1200 °C to only 1060 °C over this range. The Tg of vitreous boric oxide ranges from 200 C for glasses containing as much as 1 wt% H2O, to over 300 °C for the driest... 

Vitreous silica is by far the most refractory of the common commercial glasses, with glass transformation temperatures ranging from about 1050 to 1200 °C as a function of the hydroxyl content of the glass. The glass transformation temperature and the isothermal viscosity decrease as the hydroxyl content of vitreous silica increases. The synthetic vitreous silicas also contain residual chlorine, which acts in the same way as hydroxyl in reducing Tg and the viscosity. Other impurities have a relatively small effect on Tg and viscosity. 

A log-log plot of the isothermal viscosity as a function of the deformation rate. 

On the basis of this assunq>tion, an em nbrical model was proposed to describe isothermal viscosity change of the epoxy resin compounds du g their mold filling process. 

Fig. 14.15. Behavior of the viscosity of ethane in the vapor j ase along selected isotherms viscosity at the pressure of 1 bar.

Figure 9.9 Isothermal viscosity of graphene oxide (GO)-modified epoxy samples at 80 °C.

Figure 10.24 The viscosity behaviour of the oxyfluoride glass 32Si02-9AlOij-31.5CdF2-18.5PbF2-5.5ZnF2-3.5ErF3 (mol %) is shown when ramped at 10°C/min up to 515°C and then held isothermally. Viscosity first rises due to the changing nature of the residual viscous liquid as the nanocrystals grow, then falls as the residual supercooled liquid is heated, and finally viscosity gradually increases as the matrix...

---