《5. Time Temperature Superposition Principle 2016-14》.pdfVIP

5. Time-Temperature Superposition Principle • It is thought that there is a general equivalence between time and temperature dependence of the viscoelastic properties of polymers • For instance a polymer that display rubbery characteristics under a given set of testing conditions can be induced to show glassy behaviour by either: ⇒ reducing the temperature ⇒ increasing the testing rate or frequency 5. Time-Temperature Superposition Principle • This type of behaviour is seen by examining the variation of the shear compliance, J, of a polymer with testing frequency measured at different temperatures Shear compliance, J, data for polyisobutylene over a range of temperatures (-35 to 80°C). 5. Time-Temperature Superposition Principle • It was found empirically that all the curves could be superposed by keeping one fixed and shifting all the other by different amounts (a shift factor aT ) horizontally parallel to the log ω axis Example of the time–temperature superposition principle using shear compliance, J, data for polyisobutylene. 5. Time-Temperature Superposition Principle • The shift factor aT may be defined as follows: ⇒ choose arbitrary reference temperature T to fix one curve