Dresden 2026 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 13: Charged Soft Matter, Polyelectrolytes and Ionic Liquids
CPP 13.4: Talk
Monday, March 9, 2026, 16:00–16:15, ZEU/0260
Molecular Mechanisms Underlying LCST and UCST Transitions in Thermoresponsive Ionic Liquids — •Hussen Oumer Mohammed1,2, Abel De Cozar1,2, and Ronen Zangi1,2 — 1Donostia International Physics Center (DIPC), Donostia, Spain — 2University of the Basque Country UPV/EHU, Donostia, Spain
We investigate liquid-liquid phase separation (LLPS) of ionic liquid (IL)-water mixtures through atomistic MD simulations. Two model systems are studied: [P4444] [TMBS], which exhibits a lower critical solution temperature (LCST) phase separation, and [Hbet][Tf2N], which displays an upper critical solution temperature (UCST) behavior.
Aiming to elucidate the driving forces governing the two types of phase separation, we performed a detailed analysis of energy decompositions, HB networks, and microstructural organizations. We find that for [P4444][TMBS]/water phase demixing, increasing temperature weakens IL-water HB, augments the enthalpic penalty of hydration, and favors ion pairing and mesoscale segregation. Conversely, for [Hbet][Tf2N]/water demixing, cooling enhances water self-networking and suppresses ion hydration, promoting like-like association, while heating disrupts the water network and re-establishes miscibility through stronger ion-water HB.
By shedding light on these molecular-level mechanisms underlying those behaviors in distinct ILs, this study offers a predictive simulation-based framework for the rational design of thermoresponsive draw solutes in FO desalination, enabling tunable and energy-efficient regeneration cycles.
Keywords: Ionic Liquids; LCST; UCST; Phase separation; MD simulation