Effect of Functional Groups on Neopentane and Adamantane Derivative Plastic Crystal Phase Transition in Molecular Simulations

Huge latent heat from the solid-solid phase change in certain plastic crystals can be leveraged for solid-state refrigeration, which is a green alternative to current cooling technologies. Although several promising materials have been identified in recent years, meeting the specific operation conditions required for solid-state refrigeration has been a challenge. Many plastic crystals' functional groups form intermolecular bonds that are responsible for the barocaloric effects and therefore can be modified to tune the existing materials for particular applications. In this work, we study the effects of the number and type of functional groups on the plastic crystal phase transition using molecular dynamics simulations. We focus on varying the functional groups of two promising classes of materials, the first with a neopentane base structure, present in the well-studied neopentyl glycol, and the second with an adamantane base structure. Transition temperatures calculated from molecular dynamics simulations differ from experimental values by 3% to 20%. Noncovalent interaction energies, computed with quantum chemical simulations, correlate well with the change in transition temperature. We observe clear trends in the variation of the structural and kinetic properties as a result of the functional changes with both base structures. An increase in the number of functional groups results in higher transition temperatures due to noncovalent bond formation. Higher electronegativity and polarizability of the functional groups are also observed to lead to higher transition temperatures. Finally, for the same number and type of functional groups, simulations show that adamantane derivatives consistently exhibit transition temperatures higher than those of their neopentane counterparts. These results suggest that functional group modification can be used reliably to tailor barocaloric plastic crystals for particular applications.