Single Molecule and Nonlinear Spectroscopic Studies of Water and Other Liquids Above and Below the Glass Transition

Iowa State University, Ames IA

Investigators

Abstract

The goal of the is project is to attain a deeper molecular level understanding of the dramatic slowing down of the molecular relaxation processes (rotations, translations) as the temperature of a supercooled liquid approaches the glass transition temperature (Tg). This challenging problem on the nature of glass and the glass transition remains as one of the most important in solid-state physics and -chemistry. No microscopic theory exists that captures all salient features of the kinetic glass formation process that marks the onset of non-ergodicity. The experimental approach is unique in that it uses three laser-based spectroscopies; single molecule (SMS), photon echo (PES) and nonphotochemical hole burning (NPHB). The liquids to be studied are water, methanol and ethanol (probe molecule Al-phthalocyanine tetrasulphonate) at temperatures below and above Tg. SMS reports on molecular rotational relaxation over a ~1-4000 second time period while NPHB and PES report on optical dephasing of probe transitions on a picosecond time scale. A novel hyperquenching apparatus will be used to prepare the glasses at low temperatures which can then be warned to Tg and temperatures above Tg. The above liquids will also be studied in confined spaces of porous materials (pore sizes ranging from a few nanometers to ~ 100 nanometers). Here water is particularly interesting since the non-freezable water in contact with a pore surface is a model for biological water bound to proteins. The research will provide students with an excellent training because of the cutting edge experimental techniques to be used and because the research is both challenging and important This unique experimental approach employing three state-of-the-art laser spectroscopies and a novel apparatus for forming a glass by cooling small liquid droplets at a rate of a million degrees per second will be used to attain a molecular level understanding of the glass transition. The data will provide new insights on how the motions of molecules dramatically slow down as the liquid is cooled towards Tg. What is learned for three important liquids (water, ethanol, and methanol) may well lead to better glasses for technological applications. Because the research is cutting-edge it will provide graduate students and postdoctoral researchers with an excellent training serve them well as independent researchers with an excellent training serve them well as independent researchers in an area of high technological importance.