Spectroscopic ellipsometry as a route to thermodynamic characterization.

Area of Science:

• Materials Science
• Polymer Science
• Thermodynamics

Background:

• Synthesizing molecularly designed materials outpaces thermodynamic characterization methods.
• Connecting molecular structure to material properties requires accurate thermodynamic data.
• Traditional methods for obtaining thermodynamic quantities like thermal expansion coefficient (α) often demand large sample sizes or complex experimental setups.

Purpose of the Study:

• To establish spectroscopic ellipsometry as a viable method for thermodynamic characterization of materials.
• To clarify the relationship between ellipsometric and volumetric thermal expansion coefficients.
• To demonstrate the utility of ellipsometry-derived data for theoretical modeling and material design.

Main Methods:

• Utilized spectroscopic ellipsometry, an optical technique for thin film analysis, to measure thermodynamic data.
• Analyzed temperature-dependent data for ten polymers using both ellipsometry and macro-scale dilatometry.
• Investigated the influence of substrate mechanical confinement on thin film thermal expansion.

Main Results:

• Achieved excellent correlation between thermal expansion coefficients (α) obtained via ellipsometry and dilatometry, accounting for substrate effects.
• Demonstrated that ellipsometry-derived α can predict polymer free volume using locally correlated lattice theory.
• Discovered a linear correlation between the thermal expansion coefficient at the glass transition temperature (T_g) and T_g itself.

Conclusions:

• Spectroscopic ellipsometry offers a straightforward method for thermodynamic characterization using minimal sample quantities.
• This technique significantly expands the range of systems amenable to thermodynamic analysis.
• Ellipsometry advances the prediction of material miscibility and dynamic relaxation, underpinning materials synthesis and property design.