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| Author(s): |
Luiz Felipe de Oliveira Faria
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2015-07-30 |
| Examining board members: |
Mauro Carlos Costa Ribeiro;
Frank Herbert Quina;
Diego Pereira dos Santos;
Omar Abdel Moneim Abou El Seoud;
Munir Salomão Skaf
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| Advisor: | Mauro Carlos Costa Ribeiro |
| Abstract | |
This thesis presents a structural investigation of molten salts at low temperatures, so-called ionic liquids (ILs). These salts were studied in different phases: liquid, supercooled liquid, crystalline, and vitreous, through changes in temperature and pressure. Due to the complex phase behavior of ILs, this thesis also comprises the study of competition between the glass transition and crystallization focusing in the process of frustrated nucleation. A wide variety of ILs based on different species of cations and anions were investigated by a combination of experimental methods and computer simulations. Molecular dynamics simulations (MD) were compared with measurements of wide angle X-ray scattering (WAXS) using synchrotron radiation, so that local structural organization in the liquid phase of a series of IL could be elucidated. Raman spectroscopy has allowed the study of structural aspects of the phases formed from the changes in vibrational frequency, band shapes, and relative intensities resulting from changes in conformation or local environment experienced by the ions. The low frequency region of the Raman spectra, containing information about the intermolecular dynamics of the system, assisted in the analysis of phase transformations. Quantum Chemical Calculations helped in the assignment of vibrational frequencies observed experimentally and in the study of interactions between ions. In addition, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) contributed to the understanding of the macroscopic behavior and structural changes at low temperatures. Among the most relevant results, it is highlighted the formation of the glacial state, crystallites mixture wrapped in supercooled liquid, that have been observed only for molecular liquids, and microscopic heterogeneity in the crystallization of a protic IL at high pressures (AU) | |
| FAPESP's process: | 11/22926-7 - Raman spectroscopy and molecular dynamics of ionic liquids |
| Grantee: | Luiz Felipe de Oliveira Faria |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |