Static glass-transition temperature

Semi-empirical rules, which correlate the static glass transition temperature Ty from differential thermal analysis or dilatometry with the dynamic T(J taken from the tan 8 or E" peak, may be used with caution in analyzing two-phase systems with a dispersed rubbery phase. The dynamic Tg depends on the rubber phase volume, and it may be shifted further toward lower temperature for effectively crosslinked and grafted rubber particles because of dilatation. 

The WLF equation enables static glass transition temperatures Tg and various dynamic glass transition temperatures Tto be interconverted. To do this, the deformation times of the various individual methods must be known... 

Figure B8.2.1 shows the fluorescence spectra of DIPHANT in a polybutadiene matrix. The h/lu ratios turned out to be significantly lower than in solution, which means that the internal rotation of the probe is restricted in such a relatively rigid polymer matrix. The fluorescence intensity of the monomer is approximately constant at temperatures ranging from —100 to —20 °C, which indicates that the probe motions are hindered, and then decreases with a concomitant increase in the excimer fluorescence. The onset of probe mobility, detected by the start of the decrease in the monomer intensity and lifetime occurs at about —20 °C, i.e. well above the low-frequency static reference temperature Tg (glass transition temperature) of the polybutadiene sample, which is —91 °C (measured at 1 Hz). This temperature shift shows the strong dependence of the apparent polymer flexibility on the characteristic frequency of the experimental technique. This frequency is the reciprocal of the monomer excited-state...

Table 4.1 Parameters related to the structural relaxation for the polymers investigated by NSE glass transition temperature Tg, position of the first static structure factor peak Qmax> shape parameter magnitude considered to perform the scaling of the NSE data, and temperature dependence of the structural relaxation time...

The rates of relaxation and retardation processes above the glass temperature are strongly dependent on the viscosity and thus on the fraction of free volume present. Because the viscosity not only depends on temperature but also on static pressure (the glass transition temperature increases approximately 1 °C per 20 bar of pressure) it is not surprising that pressure also affects the viscoelastic processes. A qualitatively relation analogous to Eq. (13.121) can be readily derived (Ferry, 1980) ... 

Empirical Relationship - Empirical relationships correlating glass transition temperature of an amorphous viscoelastic material with measurement temperature and frequency, such as the William Landel Ferry equation (17) and the form of Arrhenius equation as discussed, assume an affine relationship between stress and strain, at least for small deformations. These relationships cover finite but small strains but do not include zero strain, as is the case for the static methods such as differential scanning calorimetry. However, an infinitely small strain can be assumed in order to extend these relationships to cover the glass transition temperature determined by the static methods (DSC, DTA, dilatometry). Such a correlation which uses a form of the Arrhenius equation was suggested by W. Sichina of DuPont (18). 

Table III also shows that E increases with increasing DSC T. This would be expected from restricted segmental mobility of trie high T samples. Lewis iH found that Arrhenius plots of log frequency versus reciprocal dynamic glass transition temperature for restricted and nonrestricted polymers converges to a different point in the frequency/temperature scale. From this finding, equations were derived to predict static T from the dynamic T value and vice versa. ...

In the present study, we have made X-ray diffraction, neutron diffraction with isotopic substitution, and quasi-elastic neutron scattering measurements on highly concentrated aqueous solutions of lithium halides in a wide temperature range from room temperature to below glass transition temperature, from which the microscopic behaviors of the static structure and dynamic properties of the solutions are revealed with lowering temperature. The results obtained are discussed in connection with ice nucleation, anisotropic motion of water, crystallization, and the partial recovery of hydrogen bonds. 

---