Crossover of aging dynamics in polymer glass: From cumulative aging to noncumulative aging

Abstract

The aging behavior of polymer glass, poly(methyl methacrylate), has been investigated through the measurement of ac dielectric susceptibility at a fixed frequency after a temperature shift ∆T (≤ 20 K) between two temperatures, T1 and T2. A crossover from cumulative aging to non-cumulative aging could be observed with increasing ∆T using a twin temperature (T -) shift measurement. Based on a growth law of a dynamical coherent length given by activated dynamics, we obtained a unique coherent length for positive and negative T -shifts. The possibility of the existence of temperature chaos in polymer glasses is discussed.

Thickness and Substrate Dependences of the Relaxation of Spin-Coated Polymethyl Methacrylate Ultrathin Films Supported on SiO2 and SiOH Substrates

“…The memory effect during aging is another interesting phenomenon that is shown by thin films, as first observed by Kovacs. 22 Later, Fukao et al 23,24 and Bellon et al 21 confirmed this effect in PMMA thin films via dielectric studies. They adopted a temperature cycle mode in which the sample was first cooled to a temperature, T 1 , which was <T g , and kept at T 1 for a period, τ 1 .…”

“…Advancing literature on the confinement effect in polymer systems has confirmed some unusual behaviors, such as (i) the strong dependence of the glass transition temperature, T g , on the thickness and interface conditions; − (ii) the acceleration and deacceleration of the aging dynamics in thin and ultrathin films, respectively; − (iii) the negative thermal expansion (NTE) of some glassy polymers even after prolonged, multiple annealing; − and (iv) the memory and rejuvenation effects on the aging dynamics. − …”