Aging phenomena in poly(methyl methacrylate) thin films: memory and rejuvenation effects

Area of Science:

• Materials Science
• Polymer Physics
• Dielectric Spectroscopy

Background:

• Thin films exhibit unique properties compared to bulk materials.
• Poly(methyl methacrylate) (PMMA) is a widely studied polymer with applications in various fields.
• Understanding aging dynamics is crucial for predicting material performance and longevity.

Purpose of the Study:

• To investigate the aging dynamics of poly(methyl methacrylate) (PMMA) thin films using dielectric measurements.
• To explore different aging processes, including constant-rate aging and temperature cycling.
• To analyze the influence of film thickness and temperature changes on aging behavior.

Main Methods:

• Dielectric spectroscopy was employed to measure the dielectric constant of PMMA thin films.
• Experiments involved varying aging times, temperatures, and film thicknesses.
• Temperature cycling protocols were used to study memory and rejuvenation effects.

Main Results:

• The dielectric constant generally decreased with aging time, but increased in specific conditions (long times, near glass transition temperature, thin films).
• A memory effect was observed, where aging at a specific temperature was recalled during subsequent heating.
• Significant rejuvenation occurred during negative temperature shifts (approx. -20 K), with full memory upon return to the initial temperature, indicating temperature-independent aging in this regime.

Conclusions:

• PMMA thin films exhibit complex aging dynamics influenced by temperature, time, and film thickness.
• The observed memory and rejuvenation effects highlight the non-monotonic and history-dependent nature of polymer aging.
• Thin-film geometry significantly enhances the dependence of aging on temperature cycling compared to bulk materials.