Hydrophilic, hydrophobic and supramolecular eutectic-like mixtures: from physicochemical properties to atomistic solvation scenarios for sustainable applications

This thesis explores the design and characterisation of novel eutectic-like mixtures as sustainable alternatives to conventional solvents. Using a combined experimental–computational approach encompassing calorimetry, physicochemical measurements, X-ray scattering, and molecular dynamics simulations, the work connects molecular organisation to macroscopic properties and potential applications. Three classes of systems are investigated: i) water-based deep eutectic solvents (wbDESs), ii) hydrophobic low-transition-temperature mixtures (LTTMs) derived from monoterpenoids, and iii) supramolecular DESs (SUPRADES) formed by β-cyclodextrin (β-CD) and lactic acid. In the first part, the thesis focuses on wbDESs and identifies the ChCl/water mixture as a model system, with the 4:1 water:ChCl ratio (aquoline) representing the deep eutectic composition. Aquoline exhibits low viscosity, high conductivity, and markedly enhances the solubility of all native cyclodextrins compared to pure water, with X-ray scattering confirming the absence of aggregation even near their saturation limits. Molecular simulations on β-CD further reveal that the enhanced solubility originates from a balanced ionic–aqueous solvation environment surrounding the cyclodextrin. The ChCl/water system also modulates surfactant self-assembly, inducing a morphological transition from cylindrical to ellipsoidal micelles for cationic species, while anionic surfactants retain spherical structures. The second part focuses on monoterpenoid-based LTTMs, particularly the thymol:carvacrol 1:1 mixture. Calorimetry, X-ray scattering, and molecular simulations reveal a micro-heterogeneous yet structurally organised liquid stabilised by complementary conventional and unconventional (O–H···π) hydrogen-bonding interactions between its components. This cooperative molecular network underlies the exceptional ability of the mixture to dissolve commercial polyethylene terephthalate (PET) up to 10 wt% at 150 °C. X-ray scattering indicates that the system behaves as a θ-solvent, promoting extended polymer conformations, while molecular dynamics simulations reveal that complementary hydrogen-bonding and π–π interactions between the solvent components and the polymer chains govern the high dissolution efficiency. Finally, the β-CD:LA SUPRADES is examined as a novel supramolecular solvent. X-ray scattering analyses and classical molecular dynamics simulations reveal a homogeneous liquid phase in which β-CD molecules are uniformly dispersed and stabilised through an extensive hydrogen-bond network with lactic acid. NMR studies confirm the formation of an inclusion complex with trans-anethole, supported by cooperative interactions within the solvent matrix that promote guest absorption and retention, as further evidenced by gas chromatography analyses. Overall, this thesis provides a comprehensive framework linking microscopic structuring and macroscopic performance in eutectic-like mixtures, offering fundamental insights and practical directions for their design and use as next-generation green solvents.