Transformation of Highly Stable Two-Component Glasses with Large T_g Contrast

Area of Science:

• Materials Science
• Physical Chemistry
• Amorphous Materials

Background:

• Physical vapor deposition (PVD) enables the formation of highly equilibrated amorphous states.
• Codeposited glasses, formed by simultaneously depositing multiple molecular components, are of significant technological and fundamental interest.
• Understanding the kinetic stability of codeposited glasses is crucial for their application and theoretical comprehension.

Purpose of the Study:

• To investigate the kinetic stability of codeposited glasses formed by methyl-m-toluate and methyl acetate using PVD.
• To analyze the influence of disparate glass transition temperatures (Tg) on the properties of codeposited glasses.
• To examine the dissolution rates of bilayer samples composed of components with differing Tg values.

Main Methods:

• Utilizing physical vapor deposition (PVD) to codeposit methyl-m-toluate (Tg = 170.0 K) and methyl acetate (Tg = 113.5 K).
• Heating codeposited glasses above their mixture Tg to quantify the onset temperature for the glass transition.
• Depositing bilayer samples and measuring dissolution rates of the lower Tg component into the higher Tg component for both stable and liquid-cooled glasses.

Main Results:

• Codeposited glasses exhibited a delayed return to the equilibrium liquid state above the mixture Tg across all compositions.
• Normalized onset temperatures revealed that codeposited glasses possess high kinetic stabilities, comparable to PVD glasses of pure components.
• Glass stability had minimal effect on the dissolution rate of the lower Tg component into the higher Tg component in bilayer samples.

Conclusions:

• The similar surface mobility of components during codeposition explains the observed high kinetic stabilities, despite large differences in their intrinsic Tg values.
• The findings suggest that PVD is an effective method for creating kinetically stable codeposited glasses.
• Dissolution rates in bilayer systems are largely independent of the initial glass stability of the components.