Glass transition and alpha-relaxation dynamics of thin films of labeled polystyrene

TL;DR

This study investigates how the glass transition temperature and relaxation dynamics of dye-labeled polystyrene thin films change with film thickness using dielectric measurements, revealing confinement effects on glass transition behavior.

Contribution

It demonstrates that dye-labeled polystyrene thin films are effective for studying confinement effects on glass transition dynamics via dielectric spectroscopy.

Findings

Glass transition temperature decreases with film thickness.

Dielectric relaxation time shortens as films become thinner.

Broader relaxation time distribution observed in thinner films.

Abstract

The glass transition temperature and relaxation dynamics of the segmental motions of thin films of polystyrene labeled with a dye, 4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are investigated using dielectric measurements. The dielectric relaxation strength of the DR1-labeled polystyrene is approximately 65 times larger than that of the unlabeled polystyrene above the glass transition, while there is almost no difference between them below the glass transition. The glass transition temperature of the DR1-labeled polystyrene can be determined as a crossover temperature at which the temperature coefficient of the electric capacitance changes from the value of the glassy state to that of the liquid state. The glass transition temperature of the DR1-labeled polystyrene decreases with decreasing film thickness in a reasonably similar manner to that of the unlabeled polystyrene thin films. The dielectric relaxation spectrum of the DR1-labeled polystyrene is also investigated. As thickness decreases, the $\alpha$-relaxation time becomes smaller and the distribution of the $\alpha$-relaxation times becomes broader. These results show that thin films of DR1-labeled polystyrene are a suitable system for investigating confinement effects of the glass transition dynamics using dielectric relaxation spectroscopy.