Physical Aging of Polymers

Abstract

This article provides an overview of the most important aspects of physical aging of polymers. First, we briefly introduce basic concepts of the glass transition, that is, the way a nonequilibrium glass is formed. Subsequently, after presenting the way physical aging can be monitored, we describe the main well‐established signatures of physical aging, that is, its nonexponential and nonlinear nature. The next part of the article is dedicated to recent advancements in the physical aging of bulk polymers. In this context, recent experimental activity is discussed, where the existence of multiple mechanisms for equilibrium recovery is presented. In addition, important aspects of physical aging in polymers altered by geometrical confinement are scrutinized in light of the past 20 years efforts aiming to understand glass dynamics in such conditions. It is shown how confined polymers weakly interacting with the confining medium exhibit accelerated physical aging. Importantly, such acceleration was found to be decoupled from the molecular mobility of the glass. Finally, we briefly discuss how recent advancements in physical aging of polymers in bulk and under geometrical confinement should foster experimental efforts to unveil important basic aspects of the glass transition, such as the existence of the so‐called “ideal glass.”

Long-time structural relaxation of glass-forming liquids: Simple or stretched exponential?

“…Both the stretched-exponential function and the KM relaxation rate are concepts often encountered in the field of physical aging of glasses. 10,[22][23][24][25][26][27][28] Here, the temperature is perturbed while the quantity monitored as the response may be any material property that can be measured fast enough that the sample does not relax appreciably during the acquisition time.…”

Thermal behavior of PLA plasticized by commercial and cardanol-derived plasticizers and the effect on the mechanical properties

“…Many studies were carried out in order to verify the influence of the cooling rate on the crystallization of enantiomerically pure PLA [19,20]. It was found that high crystalline fraction, characterized by large spherulites, was reached with cooling rates lower than 2 °C min −1 .…”

Fast contribution to the activation energy of a glass-forming liquid

“…physical aging | TN formalism | relaxation time activation energy P hysical aging is the term used for changes of material properties over time caused by adjustments of the positions of a system's atoms or molecules (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Although aging and degradation of materials are often due to chemical reactions, physical aging is important for amorphous solids like polymers and oxide glasses during production as well as in subsequent use.…”