Phase diagram and structure of deep eutectic solvents.

• Grant number: 25/15297-6
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2025
• End date: September 30, 2026
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Mauro Carlos Costa Ribeiro
• Grantee: Alex Yuiti Miyamoto Yokoyama
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/11983-4 - Spectroscopy signal enhancement: nanomaterials, theory, and computer simulation, AP.TEM

Abstract

Deep eutectic solvents (DES) are typically prepared by mixing a hydrogen bond acceptor and a hydrogen bond donor component, such that the mixture has a melting point well below that expected for an ideal solution. A wide variety of studies and numerous applications have been proposed over the past twenty years, but the nature of the molecular interactions and structural changes in the solid and liquid phases relative to the pure components that result in the deviation from ideality remains unclear. In this project, the system in focus is the mixture of urea with the ethylammonium chloride salt, [CH3CH2NH3]Cl. In contrast to the usual DES based on quaternary ammonium cations, in this case the anion has the possibility of accepting strong hydrogen bonds from both urea and the cation [CH3CH2NH3]+. The project will emphasize the relevance of the plastic crystal phase (solid with long-range translational order but local orientational disorder) presented by salts such as [CH3CH2NH3]Cl. Preliminary results obtained at LEM/IQ-USP for the 1:2 mixture of [CH3CH2NH3]Cl:urea suggest that in the solid phase, instead of a solid mixture of the original components, a new compound is formed. This implies a conceptual shift in the understanding of DES formation and in their classification as a simple eutectic mixture. In this project, mixtures with different molar fractions will be prepared in order to determine the solid-liquid phase diagram. To this end, the fellow will be involved with several techniques: differential scanning calorimetry (DSC), X-ray diffraction, and NMR, infrared, and Raman spectroscopy.