Structures of glasses created by multiple kinetic arrests.

Area of Science:

• Materials Science
• Physical Chemistry
• Solid-State Physics

Background:

• Amorphous solid dispersions are crucial for improving the bioavailability of poorly soluble drugs.
• Understanding the structural properties of glassy states is key to controlling drug dissolution and stability.

Purpose of the Study:

• To characterize the structural differences in glassy itraconazole (ITZ) prepared by varying cooling rates.
• To investigate the relationship between cooling rates, structural order, and molecular dynamics in ITZ glasses.

Main Methods:

• X-ray scattering was employed to analyze the structural characteristics of ITZ glasses.
• Differential scanning calorimetry was used to determine fictive temperatures (Tf).
• Dielectric spectroscopy data was correlated with structural findings.

Main Results:

• Faster cooling rates led to ITZ glasses with reduced smectic order, increased molecular spacing, and decreased lateral correlation.
• Each ITZ glass exhibited two distinct fictive temperatures (Tf), indicating multiple timescales for structural relaxation.
• The higher Tf correlated with smectic layer regularity and lateral packing, while the lower Tf related to molecular spacing.

Conclusions:

• The study demonstrates that different structural features of ITZ glasses freeze at distinct timescales, linked to molecular relaxation modes (slow δ-mode and fast α-mode).
• Cooling rate provides a method to selectively control the structural properties of ITZ glasses.
• These findings offer insights for designing amorphous solid dispersions with tailored properties.