8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P2.18Tue 611:23-14:00Statical and dynamical structure of water-methanolmixturesSimone De Panfilis, 1 Ferdinando Formisano, 2 Federica Venturini, 3 MonicaJimenez-Ruiz, 2 Helmut Schober, 2 and Giancarlo Ruocco 11 Dipartimento di Fisica - University of Roma, P. le Aldo Moro 5, 00185, Roma,Italy2 CNR-IOM-OGG c/o ILL, Grenoble, France3 Diamond Light Source, Didcot, United KingdomThe interaction of water with small or large molecules in aqueous solutions is a fundamental topicin a number of disciplines, ranging from physics to chemistry, from material science to biology.Small amphiphilic molecules, such as in lower alcohols, can be used as model probe to understandthe interactions between amphiphilic groups from much larger molecules and water. The simplestamphiphilic molecule is methanol (MeOH), with the chemical formula CH 3 OH, which consistsof a single hydrophilic (OH − ) and a single hydrophobic (CH + 3 ) group. Alcohol-water mixtures,despite their structural simplicity, are well known to possess a number of thermodynamic andtransport properties that deviate from those of an ideal binary mixture. The origin of the deviationfrom this ideal mixing must be looked for in the complex intermolecular interaction occurringbetween the polar water molecules and the amphiphiles. In aqueous solutions amphiphiles showthe tendency to self-organize into structures where the hydrophobic groups are pushed together,segregating away the water molecules, and enabling the hydrophilic regions to form hydrogenbonds more easily with the surrounding water molecules. Analogous behaviour was observedin H 2 O-MeOH mixtures, depending on the concentration variable [1]. To clarify the interplaybetween the clustering phenomenon occurring in the aqueous solutions of amphiphiles and theirstatical and dynamical properties we performed distinct x-ray and neutron scattering experimentson the simplest system, i. e. the water/methanol mixtures. We present here the results of ourexperimental work. By means of quasi-elastic and inelastic neutron scattering we probed thedynamical nature of the anomalous mixing, and we measured both the collective dynamics and thediffusion mechanism. By means of x-ray Raman scatering, we probed the local structure aroundthe O and C atomic species.[1] S. Dixit et al., Nature 416, 829 (2002).18