Aging of oriented polymer glasses

Heating scans of stretched polystyrene films with stable baselines: Preparation method of samples for thermal analysis

“…3. The result can be attributed to the entropic shrinkage of the stretched samples [8]. In fact, the shapes of stretched samples were found changing inside DSC pans before and after the heating scans [9].…”

“…10 and 11), this observation cannot be generally acceptable. Rault reported the enthalpy relaxation data concerning oriented polymer glasses using uniaxially and biaxially stretched films of polycarbonate and PS, whereas any obvious shoulder shift at T g by virtue of stretching has not been reported [8]. No shoulder shift has been observed for DSC data of stretched sheet polymer of crosslinked poly(isobutyl methacrylate) [10].…”

Relaxation of glasses: The Kohlrausch exponent

“…The volume depends on the aging time and aging temperature. Struik [3] and the author [21] showed that isotropic and oriented polymer glasses aged in a similar manner. The glass transition and the relaxation phenomena (V and H) do not depend on the so-called "order" (orientation of the chains); obviously there is no reason to invoke order parameters to explain the properties of glasses.…”

Atomistic picture of isothermal volume relaxation behavior of atactic polystyrene glass provided by a molecular dynamics simulation

“…1): at early time, the volume changes little, producing an initial plateau, this regime can last up to 1 day at 25 • C for polystyrene, 5 the duration of this regime is called incubation time τ i in Ref. 6; after a long time, no volume changes and the system reaches to an equilibrium plateau, this a) Electronic mail: chenxiaoyu.nanjing@gmail.com. regime can hardly be observed on an experimentally accessible time scale due to an extremely slow structural evolution; in the regime between the initial and equilibrium plateaus, the volume changes roughly logarithmically with the aging time, and the volume evolves following an apparent power law.…”

“…7 Volume relaxation behavior has been extensively studied via various experimental techniques. For example, dilatometry provides useful information for the changes occurring on the macroscopic scale, 5,6,8,9 spectroscopic probe and scattering methods provide a molecular level information such as free volume or the distribution of free volume 10 and density fluctuation. 11 Generally, it is believed that below T g the higher the localized mobility of polymer is, the greater the rate of volume relaxation takes place.…”