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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

Published on: January 26, 2016

Are polymers glassier upon confinement?

Jean Spièce¹, Daniel E Martínez-Tong, Michele Sferrazza

¹Laboratory of Polymer and Soft Matter Dynamics, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, 1050 Bruxelles, Belgium. snapolit@ulb.ac.be.

|June 19, 2015

Summary

Poly(l-lactide acid) thin films show thickness-dependent glass forming ability, but not glass stability. This behavior is linked to changes in free volume near interfaces, impacting thermal transitions.

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Area of Science:

Materials Science
Polymer Science
Physical Chemistry

Background:

Glass-forming systems require stability against crystallization and facile liquid-to-solid transformation.
Poly(l-lactide acid) (PLLA) is a biodegradable polymer with potential applications in thin-film devices.
Understanding thin-film behavior is crucial for material design and device performance.

Purpose of the Study:

To investigate the influence of film thickness on the thermal phase transitions of PLLA thin films.
To determine parameters for glass stability and glass forming ability in confined PLLA.
To correlate structural morphology and free volume changes with observed thermal properties.

Main Methods:

Ellipsometry was used to determine thermal phase transition temperatures (glass transition, cold crystallization, melting).
Experiments were conducted on PLLA thin films with thicknesses down to 6 nm.
Structural morphology and free volume analysis were performed to understand the physical basis of the results.

Main Results:

A strong dependence of glass forming ability on PLLA thin film thickness was observed.
Glass stability was found to be unaffected by the 1D confinement imposed by the film thickness.
Key structural and morphological features, including changes in free volume near interfaces, were identified.

Conclusions:

Film thickness significantly impacts the glass forming ability of PLLA, suggesting confinement effects are critical.
Glass stability remains robust against thickness variations, indicating intrinsic material properties dominate.
Free volume changes at interfaces play a crucial role in mediating the thickness-dependent thermal behavior of PLLA thin films.