Phase transitions and structure of deep eutectic solvents

Abstract

This PhD project will expand the scope of the research on ionic liquids carried out in the Molecular Spectroscopy Laboratory (LEM/IQ-USP) to others alternative solventes, namely, Deep Eutectic Solventes (DES). The DES are typically formed by a mixture of a H-bond acceptor component and another donor component, so that the mixture exhibits the melting temperature well below what should be expected for an ideal solution. The nature of intermolecular interactions and the resulting local structures will be studied in this work by vibrational spectroscopy (infrared and Raman). This work concerns the DES based on alkylammonium salts and carboxilic acids or poliols. The main applications of this kind of DES include CO2 absorption, and solvent for chemical reactions and biomass processing. In this project, the vibrational spectra will be obtained as a function of temperature and composition in order to follow the structural changes in both the solid and liquid phases of the components and the mixture. Thus, the disruption of the structure of the original pure components and the new specific interactions leading to the large deviation from ideal behaviour will be indentified. Methods of computational quantum chemistry will be used to support the analysis of the experimental spectra, since they provide the equillibrium configuration, molecular orbitals, and the vibrational frequencies of clusters of ions and molecules of the DES. A Diamond Anvil Cell (DAC) for high pressure vibrational spectroscopy (within the GPa range) will be used to extend the analysis of the phase diagrams by including the pressure as a variable, which an issue not usually discussed in the scientific literature on DES. Vibrational spectroscopy under high pressure is particurlarly interesting due to the effect on the H-bonds, which is usually assigned as the main reason for forming DES. (AU)