Relaxation time local segmental

FIGURE 24.1 Local segmental relaxation times for pol3miethyltolylsiloxane (PMTS) measured dielectrically as a function of temperature at constant pressure (circles) and as a function of pressure at fixed temperature (triangles). (From Paluch, M., Pawlus, S., and Roland, C.M., Macromolecules, 35, 7338, 2002.)... 

FIGURE 24.2 Local segmental relaxation times for polymethyltolylsiloxane (PMTS) from Figure 24.1 replotted as a function of specific volume. 

FIGURE 24.4 Master curves of the local segmental relaxation times for 1,4-polyisoprene (-y = 3.0) 1,2-polybutadiene (7=1.9) polyvinylmethylether (7 = 2.55) polyvinylacetate (7 = 2.6) polypropylene glycol (7 = 2.5) polyoxybutylene (7 = 2.8) poly(phenyl glycidyl ether)-co-formaldehyde (7 = 3.5) polymethylphe-nylsiloxane (7 = 5.6) poly[(o-cresyl glycidyl ether)-co-formaldehyde] (7 = 3.3) and polymethyltolylsiloxane (PMTS) (7 = 5.0) [15 and references therein]. Each symbol for a given material represents a different condition of T and P. 

FIGURE 6.8 Local segmental relaxation times (circles) and terminal shift factors (squares) for polybutadienes. The fitted VFTH equations illustrate the marked differences in temperature-dependence of the local and global dynamics (Robertson and Rademacher, 2004). 

With the help of the JG relaxation, we have deduced in the previous section that the primitive local segmental relaxation time To or its friction... 

Fig. 19. Temperature dependence of the shift factors of the viscosity (T), terminal dispersion ( ), and softening dispersion (0) of app from Ref. 73. The temperature dependence of the local segmental relaxation time determined by dynamic light scattering ( ) (30) and by dynamic mechanical relaxation (o) (74). The two solid lines are separate fits to the terminal shift factor and local segmental relaxation by the Vogel-Fulcher-Tammann-Hesse equation. The uppermost dashed line is the global relaxation time tr, deduced from nmr relaxation data (75). The dashed curve in the middle is tr after a vertical shift indicated by the arrow to line up with the shift factor of viscosity (73). The lowest dashed curve is the local segmental relaxation time tgeg deduced from nmr relaxation data (75).

Reductions of the Tg had been found in polymers confined to form a thin film on a substrate [134,135]. When the substrate is eliminated by making a free-standing thin polystyrene (PS) film, even larger reductions of Tg and the local segmental-relaxation time have been observed as the thickness of the films is decreased [136]. 

Although the local segmental relaxation occurs at higher frequencies than those covered by the frequency range of the mechanical measurements in Fig. 2.28, it was subsequently measured in the same sample by PCS, which extends measurement to times as short as 1 ps [167,168]. The measured correlation function has the KWW time dependence of Eq. (2.25) with the exponent 1 — n equal to 0.55. The local segmental relaxation times x, rewritten here as r , are plotted against temperature in... 

---