0.5% Graphene Slashed 38.8 °C Supercooling in Plastic Crystals

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• Plastic crystals offer promising thermal regulation via phase transitions.
• High energy barriers cause significant supercooling, limiting their practical use.
• Graphene incorporation is explored to overcome these limitations.

Purpose of the Study:

• To investigate graphene's effect on supercooling and energy storage in plastic crystals.
• To understand the mechanism behind supercooling inhibition and enthalpy enhancement.
• To develop a universal strategy for designing advanced plastic crystalline materials.

Main Methods:

• Incorporation of 0.5 wt % graphene into tris(hydroxymethyl)aminomethane (Tris).
• Synchrotron X-ray diffraction (XRD) and femtosecond infrared spectroscopy.
• Molecular dynamics (MD) simulations and analysis of rotational entropy and enthalpy.

Main Results:

• Supercooling was inhibited by 38.8 °C, with a 20.8% enthalpy boost.
• Graphene induced 'rotational entropy pinning', reducing entropy by 40.3% while increasing enthalpy.
• Structural transformations were observed from molecular vibrations to macroscopic lattice reorganization.

Conclusions:

• Graphene acts as a nucleation promoter and ordering template, suppressing supercooling and enhancing energy density.
• An interface-confined rotational dynamics model explains the observed phenomena.
• This strategy is applicable to various plastic crystalline systems and solid-liquid phase-change materials for thermal regulation.