Time-temperature superimposition

Figure 10.30 shows an example of DMA output for polytetrafluoroethylene. Samples of PTFE were analyzed by DMA in shear mode at a length to thickness ratio of 4 1. Figure 10.30a shows the DMA output of stress versus time versus temperature which has been converted to Fig. 10.30b by the time-temperature superimposition technique. 

The time-temperature superimposition technique allows the prediction of material properties that normally would require measurements over many months or years. To collect the necessary data, measurements of a time-dependent variable are made at a number of temperatures. The curves are shifted mathematically along the time axis until some overlap occurs and a continuous curve is formed covering several decades of time this curve is called a master curve. A master curve can be used to determine the time-dependent property as a function of time. Figure 10.30c shows total strain as a function of time and temperature for PTFE. 

Time—temperature superimposition technique allows the prediction of material properties that normally would require measurements over many months or years. To collect the necessary data, measurement of a time-dependent variable is made at a number of temperatures. The curves are shifted mathematically along the time axis until some... 

The quantities G, T,v) or G T,v) have all of the time-temperature superimposition properties associated with viscoelastic deformations of polymers and the WLF transform may effectively be applied to normalize G(T, v) data. Environmental changes may influence G s and thus G s is a direct scalar. " However, generally G (T,t )> G and factors of 10 to 10 are typical. 

Meiler and Pfeifer (493) measured 13C and H NMR spectra of carbon monoxide, carbon dioxide, and benzene adsorbed on ZSM-5 and silicalite. The 13C signal from benzene was a superimposition of two lines corresponding to relatively mobile molecules (narrow Lorentzian line) and strongly adsorbed molecules (broad asymmetric line similar to that in polycrystalline benzene). Quantitative interpretation of the spectrum was possible via the measurement of the transverse proton relaxation times, T2, as a function of temperature and coverage. Recent work involving 13C NMR studies of sorbed species is summarized in Table XX. 

Seki (1974) measured electron mobilities in TNF and PVK mixtures. The mobilities were in the range of 10-9 to 10-6 cm2/Vs and strongly field dependent. A key feature of Seki s results is the superimposition of current transients, when normalized to the transit time, for transit times varying by over two orders of magnitude. This is described as universality and a fundamental prediction of the Scher-Montroll (1975) formalism. The room temperature results are illustrated in Fig. 20. Seki argued that the free and trapping lifetimes... 

Figure 1.15. Youug s moduli vs. depth of 1 mm- and 3 mm-thick iujectioii molded PP plates measured in parallel and transverse directions to the flow injection time = 1.6 s, mold temperature = 40°C. Superimposition of microscopic view under polarized light of the associated crystalline microstructure...

---