Inverse Barocaloric Effect Arising From Chain Order‐Disorder Transitions in a Layered Alkylsulfonate

ABSTRACT

Barocaloric refrigeration technology offers a promising environmentally friendly alternative to conventional vapor‐compression refrigeration. In most barocaloric materials, applied pressure induces the order of the structure through volume contraction, leading to heat release. However, the inverse barocaloric effect arising from flexible long‐chain compounds, in which pressure drives disorder and heat absorption, remains rarely reported. Here, we report an inverse barocaloric effect in the layered alkylsulfonate, sodium 1‐octanesulfonate. Upon pressurization, the material absorbs heat from the surroundings, exhibiting a pressure coefficient of the transition temperature of −6.7 K kbar ⁻¹ , with an isothermal entropy change of 71.7 J kg ⁻¹ K ⁻¹ , and an adiabatic temperature change of 3–8 K under 1 kbar. Variable‐temperature XRD and Raman spectroscopy reveal the coexistence of monolayer and bilayer structures in the crystal, with pressure‐ and temperature‐driven changes in alkyl chain tilt and the formation of gauche defects that collectively increase conformational disorder. Structural analysis further identifies a negative thermal expansion along the c ‐axis upon heating, which underpins the unconventional pressure‐temperature coupling responsible for the inverse response. These findings establish flexible‐chain layered surfactants as a new and distinctive platform for barocaloric materials, offering unique inverse responses that expand the design strategies for high‐performance barocaloric refrigeration systems.