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Title: Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy

Abstract

While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measuredmore » negative excess entropy is a result of clustering or micro-immiscibility.« less

Authors:
; ;  [1]
  1. Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
Publication Date:
OSTI Identifier:
22657786
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 144; Journal Issue: 19; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; BONDING; ENTROPY; ETHANOL; EXPERIMENTAL DATA; HYDROGEN; INTERACTIONS; LIQUIDS; METHANOL; MIXTURES; X-RAY SPECTROSCOPY

Citation Formats

Lam, Royce K., Smith, Jacob W., and Saykally, Richard J., E-mail: saykally@berkeley.edu. Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy. United States: N. p., 2016. Web. doi:10.1063/1.4951010.
Lam, Royce K., Smith, Jacob W., & Saykally, Richard J., E-mail: saykally@berkeley.edu. Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy. United States. doi:10.1063/1.4951010.
Lam, Royce K., Smith, Jacob W., and Saykally, Richard J., E-mail: saykally@berkeley.edu. Sat . "Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy". United States. doi:10.1063/1.4951010.
@article{osti_22657786,
title = {Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy},
author = {Lam, Royce K. and Smith, Jacob W. and Saykally, Richard J., E-mail: saykally@berkeley.edu},
abstractNote = {While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measured negative excess entropy is a result of clustering or micro-immiscibility.},
doi = {10.1063/1.4951010},
journal = {Journal of Chemical Physics},
number = 19,
volume = 144,
place = {United States},
year = {Sat May 21 00:00:00 EDT 2016},
month = {Sat May 21 00:00:00 EDT 2016}
}