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Glass transition and crystallization of ionic liquids: a Raman Spectroscopy study

Grant number: 10/12717-9
Support type:Scholarships in Brazil - Master
Effective date (Start): March 01, 2011
Effective date (End): February 29, 2012
Field of knowledge:Physical Sciences and Mathematics - Chemistry
Principal Investigator:Mauro Carlos Costa Ribeiro
Grantee:Luiz Felipe de Oliveira Faria
Home Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Salts with low melting point, so-called ionic liquids, have attracted great interest in recent years due to various applications, e.g. alternative solvents in organic synthesis and electrolytes for batteries. Several ionic liquids are viscous systems, easily super-cooled, which typically exhibit glass transition at ca. 190 K. Among the ionic liquids proposed in the literature, we highlight those derived from imidazolium cations, pyridinium and alkylammonium, which can provide super-cooled liquid, vitreous and crystal. In this work, structural aspects of different phases of these systems will be investigated by Raman spectroscopy. The spectra will be studied in the region of small Raman shift, w < 200 cm-1, where modes of relaxation and intermolecular vibrational modes are coupled, and the relative contribution is strongly temperature dependent. The region of high frequencies due to normal modes of the ionic species, i.e. intramolecular dynamics, will be studied. Changes in vibrational frequencies, band shapes, and relative intensities between liquid and solid states reveal changes in local environment experienced by the ions. Raman spectra obtained as a function of temperature will be investigated and the dependence of spectral characteristics with the thermal history of the ionic liquid. The analysis of Raman spectra requires calculations by ab initio quantum chemistry methods in order to assign the vibrational frequencies observed experimentally. The project therefore aims to evaluate the importance of hindered nucleation and crystallization on the glass transition of supercooled ionic liquid.

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