Microstructure and concentration fluctuations in alcohol–Toluene and alcohol-Cyclohexane binary liquids: A small angle neutron scattering study

Abstract

The origin of concentration fluctuations in a series of binary liquids is examined by small angle neutron scattering in relation with H-bonded micellar clusters and the aggregation of alcohol-rich domains, which is also related to the well-known observation of a prepeak in diffraction spectra of alcohols. The results suggest that concentration fluctuations do not arise from size variation and re-arrangement of the mesoscopic domains but from the micellar-clusters themselves. We evaluate the scattering intensity at small angles and deduce the Ornstein–Zernike correlation lengths, the Bhatia-Thornton concentration fluctuations and the Kirkwood–Buff integrals. An alternative approach, based on the Guinier approximation was applied, indicating that the observed inhomogeneity could be related to spherical particles with diameter comparable to the H-bonded multimers. We compare the structure factor of different systems when varying the molecular interactions: the alcohol–solvent interaction has been tuned with Toluene and Cyclohexane aprotic solvents, and the amphiphilic character of the alcohol, by going from Tert-butanol to Ethanol and Methanol.