Thymol-Based Natural Deep Eutectic Solvents under Pressure: A Novel Platform for Green Solvents

Deep eutectic solvents (DESs) are emerging green alternatives to traditional solvents, yet their behavior under high pressure (HP) remains underexplored. This study examines two thymol-based eutectic mixtures─thymol:1,8-cineole (1:1) and thymol:camphor (1:1)─using a combined experimental and molecular dynamics approach. Pressure–volume–temperature (PVT) measurements were conducted across 0.1–60 MPa and 293.15–343.15 K. The two systems displayed expected density trends but exhibited markedly different internal pressure responses: a maximum for the camphor system and a shallow minimum for the cineole mixture. Molecular dynamics simulations revealed more frequent hydrogen bonding and greater structural organization in the camphor system, highlighting how molecular structure affects interactions. Changes in hydrogen bonding and internal pressure remained within 25% over the entire pressure range. These results provide molecular-level insight into pressure effects on DESs, guiding their future application in chemical processing and materials science under nonambient conditions.