Solvation Dynamics of Wet Ethaline: Water is the Magic Component

Journal Article · Mon Aug 02 00:00:00 EDT 2021 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/acs.jpcb.1c04629· OSTI ID:1865396

Alfurayj, Ibrahim ^[1]; Fraenza, Carla Cecilia ^[2]; Zhang, Yong ^[3]; Pandian, Rathiesh ^[4]; Spittle, Stephanie ^[5]; Hansen, Bryce ^[5]; Dean, William ^[4]; Gurkan, Burcu ^[4]; Savinell, Robert ^[4]; Greenbaum, Steve ^[2]; Maginn, Edward ^[3]; Sangoro, Joshua ^[5]; Burda, Clemens ^[4]

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1. Case Western Reserve Univ., Cleveland, OH (United States); Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, United States
2. Hunter College, New York, NY (United States)
3. Univ. of Notre Dame, IN (United States)
4. Case Western Reserve Univ., Cleveland, OH (United States)
5. Univ. of Tennessee, Knoxville, TN (United States)

The past two decades witnessed the development of a new type of solvent system, named deep eutectic solvents, which have become increasingly investigated because they offer new and potentially favorable properties, such as wide tunability in electrochemical, mechanical, and transport properties. Deep eutectic solvent (DES) systems are composed of at least one main solvent and an additional component that is meant to interrupt the original solvent/solvent interactions, thereby introducing lower melting points relative to each individual component. Ethaline (a 1:2 mole% mixture of choline chloride and ethylene glycol) is one of the most promising DES systems. However, it is also known to be very hygroscopic, which is a constant concern because water absorption during the use of ethaline alters its properties. Within this work, we demonstrate that modest amounts of water addition (1-10%) to ethaline are of little concern for practical use and can even lead to performance improvements, such as accelerated relaxation and solvation. In contrast, very small amounts of <1% of water lead to additional slowing of the solvent response. Thus, we suggest that the attempt to dry ethaline below 1% moisture is rather counter-productive if one attempts to achieve effective solvation and charge transport properties from DESs. This study investigates the effect of water content on the diffusional relaxation dynamics of ethaline. A set of independent spectroscopic experiments and computational simulations are aimed to provide insight into the solvent response of the DES system using femtosecond time-resolved absorption spectroscopy (fs-TA), broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR) diffusometry and broadband relaxometry, and molecular dynamics simulations (MDS) on ethaline with 0, 0.1, 1, 10, and 28.5wt% added water. For dry ethaline, we identify choline chloride as the rate-limiting solvation component in ethaline. However, the role of the solvent components changes gradually as water is added. Further, we provide quantitative solvent relaxation rates using the different presented time-resolved spectroscopic techniques and find remarkable agreement between them. Based on the solvent relaxation rates and combined with MDS, we develop a molecular understanding of the individual solvent components and their interactions in dry and wet ethaline with varying amounts of water content.

• Research Organization: Case Western Reserve Univ., Cleveland, OH (United States); Energy Frontier Research Centers (EFRC) (United States). Breakthrough Electrolytes for Energy Storage (BEES)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0019409
• OSTI ID: 1865396
• Alternate ID(s): OSTI ID: 1853228
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry Journal Issue: 31 Vol. 125; ISSN 1520-6106
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

25 ENERGY STORAGE
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organic compounds
solvents