UOXSSDWA · Ultra-fast optical and X-ray studies of solvation dynamics in water and alcohol
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2005-10-01 → 2007-09-30
- EU contribution
- €80,000
- Participants
- 1
- Scheme
- IRG
Lines connect the coordinator with its partners.
Results in brief
Final Activity and Management Report Summary - UOXSSDWA (Ultrafast optical and X-ray studies of solvation dynamics in water and alcohol)
Electrolytes are usually conducting media, in which charged ions move freely in a solvent. Now, experiments led by Dr Verner Thorsmølle and Prof. Jacques-E. Moser revealed a new mechanism for the electrical conduction in ionic liquid electrolytes. The existence of a new conduction mechanism that did not involve the transport of ions was demonstrated. T%:%: his discovery was made while looking for ways to improve the conductivity of ionic liquids, which were used as electrolytes in dye-sensitised solar cells. The peculiarity of these liquids was that they only contained ions and no neutral solvent molecule. Evaporation of the liquid and its degradation were, thus, prevented. Iodine added to iodide-based ionic liquids led to extraordinarily efficient charge transport, vastly exceeding the one expected for such viscous systems. Using terahertz time-domain spectroscopy, in conjunction with dc conductivity, diffusivity and viscosity measurements, conductivity pathways in such an ionic melt were unravelled. The resulting measurements enabled the detection of the vibrations of the ions, as well as their way to associate with each other. This achievement was made possible thanks to ultra-short laser pulses that generated THz radiation, which lay between the infrared and the microwave frequency range. This radiation had the property of interacting with mobile electrical charges and low-frequency vibrations of matter. It was thus possible to observe in an ionic liquid, containing iodide and triiodide ions, a bond-exchange phenomenon. In this scenario, an iodide ion (I-) bound to a neighbouring triiodide (I3-) ion, while at the other end of the chain a bond was broken and a new I- ion was liberated. This mechanism governing the displacement of electrical charges only implied back and forth movements over very short distances, of the order of 3 angstroms, and did not require the transport of ions over longer ranges. Thanks to the bond exchange between ions, electrical conduction remained efficient, even in viscous liquids and at very low temperature. A similar mechanism was suggested by Theodor de Grotthuss at the beginning of the 19th century to explain the conductivity of water, but had never been demonstrated for an ionic liquid. Temperature-dependent terahertz time domain spectroscopy measurements were also carried out on some ionic liquid mixtures containing the iodide-iodine redox couple. It was discovered that beyond a threshold concentration of iodine, new phases appeared between liquid and solid phases that allowed for increased conduction. These phases were found to be consistent with complementary X-ray studies of the melts. These novel results were very important for the fundamental understanding of conduction in room temperature molten salts and for applications where ionic liquids were used as charge transporting media such as in batteries and dye-sensitised solar cells.
Data: CORDIS, © European Union
Project objective
Atomic ions in liquids are of vital importance in almost all biological and chemical processes. In addition, they can serve as simple model systems for understanding the details of hydration and solvation dynamics in liquids. Solvation dynamics involves changes of the solvent shell structure around a solute upon electronic changes of the solute.It is therefore at the core of condensed phase chemistry and biology. Femtosecond optical pump-probe spectroscopy has been a revolutionary tool for observing real time motion of simple molecular systems, with its inherent ability to temporally resolve phenomena at the fundamental timescales of nuclear and electronic motion.However, for a more complete description of the dynamics of even more complex systems, which would also include structural determination, we propose a novel approach, which combines ultrafast optical and X-ray spectroscopies in a pump-probe scheme. Such a technique will allow a direct visualization of the structural changes of the solvent shell around atomic ions in real time.In this pump-probe scheme an ultrafast laser pulse excites the solute, while another optical or X-ray pulse takes snapshots of the changes resulting from the excitation as a function of time after excitation. In this technique, the picosecond X-ray pulses are produced in a synchrotron and the detected signal is the X-ray absorption of the solute.The detected signal carries information about the electronic structure changes of the solute (via X-ray Absorption Near-Edge Structure), as well as the geometric changes of the solvent shell (via Extended Xray Absorption Fine Structure).Using time-resolved X-ray absorption spectroscopy in this configuration we propose to study the solvation process around halogen anions and metallic cat ions. With this approach we hope to capture, for the first time, the structural details of the solvation process, and to gain insight into the hydration process and liquid state.
Original text from CORDIS.
Participants
- ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE · LAUSANNECoordinatorSwitzerland
Links
Data: CORDIS, © European Union