Evidence of the Giant Barocaloric Effect in the PVA-Slime System by Molecular Dynamics Simulations

Advancements in the study of the barocaloric effect in polymers have opened promising applications in both the scientific and industrial fields. Among these, elastic polymers based on poly-(vinyl alcohol) (PVA), such as slimes, have shown significant potential for solid-state refrigeration and thermal battery applications due to their notable pressure-induced thermal response, which occurs without an associated structural phase transition. Thus, current research focuses on understanding the mechanism behind this response to applied pressure with the aim of optimizing its thermal performance. Therefore, we employed a molecular dynamics simulation in order to explore the barocaloric effect in the Slime system. We used pure PVA chains cross-linked by tetrahydroxyborate ions to provide further details about our Slime system, promoting a greater proximity between polymeric chains. Our results reveal that these connections reduce the free volume in the Slime system compared to pure PVA. This, combined with the applied simulated pressure, decreases the mobility of the polymer chains, lowering their kinetic energy while favoring potential energy. As a result, this contributes significantly to the change in internal energy and, consequently, to the barocaloric effect. Thus, our investigation shows a significant increase in entropy from 56 JK^-1 kg^-1 for pure PVA to 295 JK^-1 kg^-1 Slime system and temperature change from 3 to 26 K at 300 MPa. These findings highlight the importance of cross-linking between polymer chains, which enhances the barocaloric effect in this system type, offering promising prospects for practical applications.