Nanometer-scale structures in soft condensed-phase systems

The scientific target of this project proposal is to clarify the nanometer-scale structures formed by molecules coupled by resonant intermolecular vibrational interactions in soft condensed-phase systems, such as molecular liquids and biomolecular aggregates.These studies will be carried out in order to better understand the formation of nanometer-scale structures in biologically relevant environments, and the dependence of these structures on concentration and temperature. The experimental work will be carried out in form of an already existing international cooperation between the Institute of Physics and Biophysics at the University of Salzburg (Austria) and the Department of Physical and Inorganic Chemistry at the University of Bologna (Italy), as a continuation of the collaboration established back in 1994. It will consist of the Raman spectroscopic study of effects of intermolecular resonant vibrational interactions on the band shape observed in the vibrational spectra of molecular liquids. At the same time theoretical investigations and computer simulations will be carried out at the Department of Chemistry of the Shizuoka University (Japan), extensively analyzing relative orientations of molecules in addition to their relative positions. Not only static structures but also short-time dynamics (on the pico- to nanosecond time scale) will be considered. Although the informal cooperation between the mentioned institutions was already started in 1996, the purpose of this project proposal is to establish a closer collaboration between the Japanese applicant and the Austrian applicant, including visits at each other laboratory for more extensive research work. The liquid systems which will be treated in this project can be classified into three categories: 1) binary liquid systems with nanometer-scale structures formed by hydrogen-bond networks, such as water- alcohol and peptide-water mixtures; 2) polar and hydrogen-bonded neat liquids confined in narrow space in porous glasses and zeolites; 3) liquid systems with large effects of intermolecular electrostatic interactions, such as solutions of electrolytes in organic solvents.

The project`s most important result is the successful use of the intermolecular resonant vibrational coupling between vibrational modes of neighbouring molecules of the same species in order to determine the nanoscale structure of a molecular liquid and the change of this structure with the change of thermodynamic parameters (concentration, temperature, density). Both experimental methods and computer simulations were used in order to obtain a deeper understanding of the nanoscale structure of the molecular liquid considered. The experimentally observable signature of this nanostructure is the noncoincidence splitting of spectroscopically observable bands belonging to suitable chosen Raman active vibrational modes of molecules in the liquid, as function of the polarisations of the incident monochromatic excitation light and of the scattered Raman light. Part of the research work was dedicated to the nanostructures of polar and of hydrogen-bonded solutes and their change with dilution in nonpolar and polar solvents. Extensions of these studies dealt with the nanostructure of a nematic liquid crystal during the phase transition from nematic to isotropic. Some highly successful activities dealt with the spectroscopic evidence of critical density fluctuations of fluids close to their critical point for the gas- liquid phase transition, and manifested by the critical line broadening phenomenon. The project has been carried out in an international context by researchers from Austria, Germany, Japan, and Italy.