Hydrogen bond structure and associated dynamics in micro-heterogeneous and in phase separated alcohol-water binary mixtures: A THz spectroscopic investigation

Despite being a simple and widely studied solution, a correlation between the structure and dynamics of the hydrogen bond (HBond) network in alcohol-water binary mixtures remains highly debatable. The present work combined Terahertz time domain spectroscopy (TTDS) and Terahertz-Fourier transform infrared (THz-FTIR) spectroscopy covering a wide frequency window of 0.3-18 THz, which probes most of the intermolecular rotovibrational modes of water, to extract an extensive idea on such aspect of the binary mixtures. This study demonstrates a unified picture of the solute concentration-dependent HBond network structure and its associated dynamics in alcohol-water binary mixtures considering micro- and macro-scale (for partially water-soluble alcohols) phases present inside the systems. The work extensively took into account both the factors of hydrophobic chain length and macroscopic self-aggregation of alcohols to present a comprehensive view of HBonded intermolecular networks in binary mixtures. We found a balance between the local homo-molecular and crossmolecular solvation which leads to a micro/macro scale self-aggregation for various alcohol-water mixtures.