Raman spectroscopy of ionic liquids under high pressure

• Grant number: 10/11999-0
• Support Opportunities: Regular Research Grants
• Start date: December 01, 2010
• End date: November 30, 2012
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Mauro Carlos Costa Ribeiro
• Grantee: Mauro Carlos Costa Ribeiro
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Room temperature molten salts, the so-called ionic liquids, have been an issue of great interest in the last years proper to many different applications, e.g. alternative solvents for synthesis and electrolytes for electrochemical devices. Several ionic liquids are viscous liquids, which are easily supercooled with typical glass transition temperature Tg ~ 190 K. In this work, low-frequency Raman spectra (w < 200 cm-1) of ionic liquids will be investigated as a function of pressure. Raman spectra within the low-frequency range result from fast (picoseconds) relaxation processes and intermolecular vibrational dynamics. In previous works in the Molecular Spectrocopy Laboratory (LEM) of IQ-USP, we studied the temperature dependence of the relative contribution of relaxation and vibration, while in this work we intend the study of the pressure effect. The relevance of pressure changes in studying glass-forming liquids relies on the fact that pressure addresses the role played by density, and therefore free volume, from thermal energy effects. The aim of this work is to compare temperature and pressure effect, since recent proposals suggest that free volume or thermal energy may dominate the behaviour of fast relaxations in different situation, in which free volume should the most important factor above Tg. (AU)