Polyol-based deep eutectic solvents: betaine versus choline chloride

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Phys. Chem. Chem. Phys., 2026, Advance ArticleDOI: 10.1039/D6CP00104A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Gabriel Teixeira, Dinis O. Abranches, Gangqiang Yu, Christoph Held, Luís M. N. B.…

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Polyol-based deep eutectic solvents: betaine versus choline chloride

* Corresponding authors

a CICECO – Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, Aveiro, Portugal

b Laboratory of Thermodynamics, Department of Biochemical and Chemical Engineering, TU Dortmund University, Emil-Figge-Street 70, Dortmund 44227, Germany

c Faculty of Environment and Life, Beijing University of Technology, 100 Ping Le Yuan, Chaoyang District, Beijing, China

d CIQUP, Institute of Molecular Sciences (IMS), Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, Porto 4169-007, Portugal

e CIMO, LA SusTEC, Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal
E-mail: [email protected]

Abstract

This work investigates the potential of betaine as a substitute for choline chloride in the formation of polyol-based DES. The solid–liquid equilibrium (SLE) phase diagrams of binary mixtures of betaine with one polyol (ethylene glycol, 1,3-propanediol, glycerol, meso-erythritol, xylitol, or sorbitol) were studied across the entire composition range. Experimental measurements of the phase diagrams were limited by the thermal degradation of betaine and by the boiling points or high viscosities of some polyols. Overall, betaine exhibited negative deviations from ideality, while most polyols displayed near-ideal behaviour. COSMO-RS, a thermodynamic model, satisfactorily predicts these deviations from ideality and the observed phase behaviour. Mixtures of betaine and polyols yielded a narrower liquid-phase window for room-temperature applications than the corresponding choline chloride systems. The cross-association of betaine with polyols is more favourable than its self-association, and stronger interactions between the polyols and betaine than with choline chloride are expected, leading to more negative deviations; thus, the smaller melting temperature depression must result from a higher enthalpy of fusion of betaine than that of choline chloride.