A Fresh Perspective on the Internal Plasticizing Effect in Non-Polymeric Glass-Formers

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Chemistry

Background:

• The internal plasticizing effect, where flexible substituents lower glass transition temperature (Tg), is well-known in polymers.
• Its application to low-molecular-weight compounds is a recent area of interest.

Purpose of the Study:

• To provide direct evidence of internal plasticization in low-molecular-weight glass-formers.
• To investigate the influence of molar mass and molecular flexibility on Tg.

Main Methods:

• Comparative analysis of thermal and dynamic properties of structurally related compounds.
• Differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS).
• Density functional theory (DFT) calculations.

Main Results:

• Increasing molar mass via atom substitution (e.g., Cl to Br) without changing flexibility decelerated dynamics and raised Tg.
• Elongating flexible substituents with increased molar mass lowered Tg and enhanced dynamics.
• Internal molecular flexibility was identified as a key factor controlling Tg.

Conclusions:

• Internal plasticization is a fundamental mechanism influencing the properties of molecular glass-formers.
• Molecular flexibility and conformational diversity are crucial for glass transition phenomena.