Abstract
Plastic crystal neopentylglycol (NPG) exhibits colossal barocaloric effects (BCEs) with record-high entropy changes, offering exciting prospects for the field of solid-state cooling through the application of moderate pressures. Here, we show that the intermolecular hydrogen bond plays a key role in the orientational order of NPG molecules, while its broken due to thermal perturbation prominently weakens the activation barrier of orientational disorder. The analysis of hydrogen bond strength, rotational entropy free energy and entropy changes provides insightful understanding of BCEs in order-disorder transition. External pressure reduce the hydsrogen bond length and enhance the activation barrier of orientational disorder, which serves as a route of varying intermolecular interaction to tune the order-disorder transition. Our work provides atomic-scale insights on the orientational order-disorder transition of NPG as the prototypical plastic crystal with BCEs, which is helpful to achieve superior caloric materials by molecular designing in the near future.
Highlights
Plastic crystal neopentylglycol (NPG) exhibits colossal barocaloric effects (BCEs) with record-high entropy changes, offering exciting prospects for the field of solid-state cooling through the application of moderate pressures
We show that the formation of hydrogen bond ladder between hydroxy of adjacent NPG molecule columns restricts the rotation of molecules at low temperature, while its breaking significantly lowers the activation barrier
NPG molecule consists of five carbon atoms that form the tetrahedron, in which two carbon atoms are bonded to hydrogen atoms in the methyl group (CH3), while the rest two are attached to the hydroxymethyl group (CH2OH)
Summary
Plastic crystal neopentylglycol (NPG) exhibits colossal barocaloric effects (BCEs) with record-high entropy changes, offering exciting prospects for the field of solid-state cooling through the application of moderate pressures. The analysis of hydrogen bond strength, rotational entropy free energy and entropy changes provides insightful understanding of BCEs in order-disorder transition. Our work provides atomic-scale insights on the orientational orderdisorder transition of NPG as the prototypical plastic crystal with BCEs, which is helpful to achieve superior caloric materials by molecular designing in the near future. Most vibrational frequencies of the NPG molecule are identified in theoretical calculations and Raman spectroscopy measurements, among which only the O–H stretching modes are significantly weakened and pressure dependent These results provide fundamental understandings of NPG as prototypical plastic crystals in order–disorder transition
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