- Yuya Shinohara, The University of Tennessee, Knoxville
Viscosity is a fundamental property of liquid, and yet, the understanding of its microscopic origin is insufficient despite an immense amount of studies. Recent progress in inelastic X-ray/neutron scattering makes it possible to obtain inelastic-scattering spectra over a wide range of energy (E) and momentum transfer (Q) with a high E- and Q-resolution, thereby enabling to calculate the time-dependent pair correlation function called the Van Hove function via double-Fourier transformation. With this novel approach, we have determined the spatial and temporal correlations of the molecular motion of water and its temperature variation on a picosecond timescale and subnanometer in length scale. The results show that the timescale of the decay in the Van Hove function is directly related to the Maxwell relaxation time, which is proportional to macroscopic viscosity. We applied this approach to an aqueous solution of NaCl and found that the increase in the decay time of the Van Hove function agrees with the increase in viscosity. These results validate our earlier finding that the topological changes in atomic/molecular connectivity govern the viscosity of liquids. The approach used in this study offers a powerful experimental technique for investigating local real-space dynamics of liquids and can be used for various liquids such as electrolytes and lubricants.
Refreshments will be served at 9:30.