Simultaneous Analysis of Equilibrium Fluctuations at the Surface and in the Bulk of a Binary Liquid Mixture by Dynamic Light Scattering.

For the first time, we demonstrate that it is possible to simultaneously analyze microscopic fluctuations at the surface and in the bulk of a binary liquid mixture by dynamic light scattering in macroscopic thermodynamic equilibrium. For a model system containing n-octacosane and ethanol, three individual signals distinguishable in the time-resolved analysis of the scattered light intensity appear on different time scales. One oscillatory signal from surface fluctuations at the vapor-liquid interface in the short-time range and two exponential Rayleigh signals from fluctuations in temperature and concentration in the bulk of fluid in the long-time range could be associated with hydrodynamic modes.

Characterization of Water Solubility in n-Octacosane Using Raman Spectroscopy.

In this study, we demonstrate the ability of polarization-difference Raman spectroscopy (PDRS) to detect dissolved free water molecules in a n-octacosane (n-CH) liquid-rich phase, and thus to determine its solubility, at temperatures and pressures relevant to the Fischer-Tropsch synthesis. Our results for the pure alkane reveal thermal decomposition above a temperature of 500 K as well as an increase of gauche conformers of the alkane chains with an increase in temperature. For binary homogeneous mixtures, raw spectra obtained from two different polarization scattering geometries did not show a relevant signal in the OH stretching frequency range.