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Publication abstract: The temperature-dependent hydration structure of long-chain fatty acids and alcohols at air-water interfaces has great significance in the fundamental interactions underlying ice nucleation in the atmosphere. We present an integrated theoretical and experimental study of the temperature-dependent vibrational structure and electric field character of the immediate hydration shells of fatty alcohol and acid headgroups. We use a combination of surface-sensitive spectroscopy, surface potentiometry, and ab initio molecular dynamics simulations to elucidate detailed molecular structures of the octadecanoic acid and octadecanol (stearic acid and stearyl alcohol) headgroup hydration shells at room temperature and near freezing. Results reveal that the hydration shells for both compounds screen their polar headgroup dipole moments reducing the surface potential at low surface coverages; at higher surface coverage, the polar headgroups become dehydrated, which reduces the screening, correlating to higher observed surface potential values. Lowering the temperature promotes tighter chain packing and an increase in surface potential. The chain packing correlates with stronger intermolecular interactions between the fatty compound headgroup and its hydration shell as shown by infrared reflection absorption spectroscopy (IRRAS). This in turn disrupts the water-water hydrogen bonds at near freezing temperatures. Using ab initio molecular dynamics (AIMD) calculations on cluster systems of propanol + 6 H2O and propionic acid + 10 H2O, a spectral decomposition scheme was developed to correlate the OH stretching motion with the IRRAS spectral features. These findings challenge assumptions that point to ice templating as the preferred mechanism for ice nucleation at aqueous surfaces. Research Data Curation Program, UC San Diego, La Jolla, 92093-0175 (https://lib.ucsd.edu/rdcp) Vazquez de Vasquez, Maria G.; Carter-Fenk, Kimberly A.; McCalsin, Laura; Beasley, Emma E.; Simpson, Jessica B.; Allen, Heather C. (2021). Data from: Hydration and Hydrogen Bond Disorder of Octadecanoic Acid and Octadecanol Films on Water at 21 ᵒC and 1 ᵒC. In Center for Aerosol Impacts on Chemistry of the Environment (CAICE). UC San Diego Library Digital Collections. https://doi.org/10.6075/J05X2934
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