My talk on "Fluctuations in water and their relation to the hydrophobic effects near model surfaces and proteins" was the first of the day, and I was very happy that it was well received.
After the coffee break, Taku Iiyama (Shinshu University, Japan) talked about "Structural Understanding of Water Confined in Hydrophobic Nanopores". The talk was about experimental probes of water structure in activated carbon, an amorphous form of carbon with pores of size 0.7 - 1.5 nm that absorbs large quantities of water (1 g / g). Not sure that I could extract a main message from the talk.
The highlight of the day came after lunch, when a couple of us went to the Aiguille du Midi, a tiny outcrop almost at the top of the French Alps (top of first photo). The climb by cable car is absolutely stunning and the views at the top make it very worthwhile. Here are a few pictures (the Mont Blanc, the highest mountain in Europe, is the round thing in the background of the 3rd photo):
In the afternoon, Volker Kempter made "Some General Remarks on Ionic Liquids". An ionic liquid consists entirely of ion pairs ("molten salts"). Liquid below 100 C: why? ions tend to be large and complicated, so the interaction between oppositely-charged ions is weaker than in atomic salts. Properties: very low vapor pressure at room temperature (<10^-9 mbar) => can do experiments in Ultra-High Vacuum. At elevated temperatures, ILs can be evaporated as ion-pairs. Properties tunable in a wide range by varying molecular structure. In constrast to organic solvents, not generally poisonous. Applications: Electrochemistry (batteries, electroplating, dye-sensitized solar cells), "Engineering fluids": extraction, extractive distillation, lubrication, etc. What about water in ionic liquids? Usually an impurity, so to get rid of it, it's useful to know how it interacts with the liquid.
Methods typically used to study ionic liquids: photoelectron spectroscopy (UPS, XPS), metastable induced electron spectroscopy (MIES), mass spectrometry (QMS), quantum-chemical "first principles" calculations (DFT, CAS-SCF). Accompanied by high-resolution energy loss spectroscopy (HREELS). Theoretical methods include Quantum Chemistry, AIMD and MD with classical potentials.
The final talk of the day was by Yukio Ouchi, on "Nonlinear Vibrational Spectroscopy and Molecular-Dynamics on Water/Ionic Liquid Interfaces" (Nagoya University, Japan). Main Q: how molecular and ionic species behave at water surfaces or interfaces? Room Temperature Ionic liquids (RTILs) were first synthesized by P. Walden in 1914 ([C_2 H_5 NH_3] NO_3, mp 12 C). Not very stable at ambient conditions, only until 1992 were they revived by Wiles & Zaworotko (1992): ([C_2mim] BF_4, mp -12 C). Properties of RTILs: liquid phase at reasonable temperatures, negligible vapor pressure, low flammability, reasonbly high conductivity, chemical stability (based on electrostatic interaction). But what else? RTILs tend to be *polar* liquids, but they are usually immiscible with water. ILs have molecular structure, and so they don't just interact like isotropic charges: their interactions look much more like coordination chemistry: "molecular ordering via coordination chemstry" (Lopes et al, JPCB 110 (06) 330). They also behave a little bit like surfactants, with polar and non-polar parts that segregate, i.e., you have mesoscopic ordering. (Example: [C8mim][OTf] and SDS look almost identical) For example, on the surface of ionic liquids, you get surface "nano-freezing", detectable by X-ray diffraction. In general, ionic liquids near solid surfaces are very structured. Interesting bio app in separation of proteins dissolved in water mediated by ionic liquids and their interesting structure near water: H. Ohno, PCCP (2012).
Now, they use IR-Vis Sum Frequency Generation (IV-SFG). In surfactant systems beyond the critical micelle concentration, you get a Langmuir layer of the interface. Can you see something similar in ionic liquids? Apparently yes: if you slowly increase the concentration of an ionic liquid (in what solvent??), the surface density of ions increases, up to a CMC, beyond which the surface density of ions plateaus (I was a bit lost about how this resulted from the SFG data). There was some discussion of the orientation of the ions at the interface, where RTILs and surfactants behaved very differently, but I'm afraid I didn't really understand it.
Although much of the talk after this point went over my head, one thing stuck out: ionic liquids seem to be a fascinating subject, and I should learn more about them. They have hints of surfactant behaviour, block copolymer behaviour and more usual liquid-state behaviour (e.g. surface tension). Lots of puzzles and MD work to do. The force field that Ouchi was using were due to Lopes (2004).
That's all for today.
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