Anisotropy and anharmonicity in polystyrene stable glass.

Area of Science:

• Materials Science
• Polymer Physics
• Optical Materials

Background:

• Stable polymer glasses are crucial for advanced applications.
• Understanding their anisotropic properties and thermal behavior is essential.
• Physical vapor deposition (PVD) offers a route to creating these glasses.

Purpose of the Study:

• To characterize optical anisotropy in stable polymer glasses using ellipsometry.
• To measure and compare the thermal expansivity of stable glasses versus ordinary glasses.
• To investigate the influence of fictive temperature on these properties.

Main Methods:

• Ellipsometry was employed to measure birefringence, quantifying in-plane vs. out-of-plane refractive index.
• Thermal expansivity was measured for both stable and ordinary (rejuvenated) polymer glasses.
• Polystyrene samples with varying chain lengths (N=6-12) and fictive temperatures were studied.

Main Results:

• Birefringence values were found to be less than 0.002 in PVD-prepared polystyrenes.
• Stable glasses exhibited lower thermal expansivity than ordinary glasses.
• The difference in thermal expansivity increased as the fictive temperature decreased.

Conclusions:

• PVD is a viable method for producing polymer glasses with low optical anisotropy.
• Stable polymer glasses possess distinct thermal expansion characteristics compared to rejuvenated glasses.
• Fictive temperature significantly impacts the thermal expansivity of stable polymer glasses.