Achieving dynamic behaviour and thermal expansion in the organic solid state via co-crystallization

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Thermal expansion describes how materials change size with temperature.
• Positive thermal expansion (PTE) is common, but negative thermal expansion (NTE), where materials shrink upon heating, is rare.
• Controlling thermal expansion is crucial for material design and applications.

Purpose of the Study:

• To demonstrate a novel method for achieving dynamic molecular motion and controlled thermal expansion in organic solids.
• To explore the use of co-crystallization to fine-tune thermal expansion properties.
• To investigate the potential for colossal and negative thermal expansion in engineered organic materials.

Main Methods:

• Co-crystallization of organic solids using a dynamic component and a systematically varied second component.
• Characterization of the resulting co-crystals' thermal expansion coefficients.
• Investigation of molecular motion within the solid state.

Main Results:

• Successfully achieved dynamic molecular motion and tunable thermal expansions in organic co-crystals.
• Demonstrated a range of linear thermal expansion coefficients, from colossal to near-zero.
• Observed rare instances of negative thermal expansion (NTE) in two co-crystal systems.

Conclusions:

• Co-crystallization is an effective strategy for designing organic solids with predictable and tunable thermal expansion properties.
• The developed approach enables control over molecular motion, paving the way for predesigned thermal expansion behaviors.
• This work expands the understanding of negative thermal expansion and offers a pathway for creating advanced functional materials.