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Chemical signatures of surface microheterogeneity on liquid mixtures

Enami, Shinichi and Ishizuka, Shinnosuke and Colussi, Agustín J. (2019) Chemical signatures of surface microheterogeneity on liquid mixtures. Journal of Chemical Physics, 150 (2). Art. No. 024702. ISSN 0021-9606. doi:10.1063/1.5055684.

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Many chemical reactions in Nature, the laboratory, and chemical industry occur in solvent mixtures that bring together species of dissimilar solubilities. Solvent mixtures are visually homogeneous, but are not randomly mixed at the molecular scale. In the all-important binary water-hydrotrope mixtures, small-angle neutron and dynamic light scattering experiments reveal the existence of short-lived (<50 ps), short-ranged (∼1 nm) concentration fluctuations. The presence of hydrophobic solutes stabilizes and extends such fluctuations into persistent, mesoscopic (10–100 nm) inhomogeneities. While the existence of inhomogeneities is well established, their impacts on reactivity are not fully understood. Here, we search for chemical signatures of inhomogeneities on the surfaces of W:X mixtures (W = water; X = acetonitrile, tetrahydrofuran, or 1,4-dioxane) by studying the reactions of Criegee intermediates (CIs) generated in situ from O_3(g) addition to a hydrophobic olefin (OL) solute. Once formed, CIs isomerize to functionalized carboxylic acids (FC) or add water to produce α-hydroxy-hydroperoxides (HH), as detected by surface-specific, online pneumatic ionization mass spectrometry. Since only the formation of HH requires the presence of water, the dependence of the R = HH/FC ratio on water molar fraction xwxwexpresses the accessibility of water to CIs on the surfaces of mixtures. The finding that Rincreases quasi-exponentially with xwxw in all solvent mixtures is consistent with CIs being preferentially produced (from their OL hydrophobic precursor) in X-rich, long-lived OL:X_mW_n interfacial clusters, rather than randomly dispersed on W:X surfaces. R vs xwxwdependences therefore reflect the average ⟨m, n⟩ composition of OL:X_mW_n interfacial clusters, as weighted by cluster reorganization dynamics. Water in large, rigid clusters could be less accessible to CIs than in smaller but more flexible clusters of lower water content. Since mesoscale inhomogeneities are intrinsic to most solvent mixtures, these phenomena should be quite general.

Item Type:Article
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URLURL TypeDescription
Enami, Shinichi0000-0002-2790-7361
Ishizuka, Shinnosuke0000-0002-5915-3576
Colussi, Agustín J.0000-0002-3400-4101
Additional Information:© 2019 Published under license by AIP Publishing. Submitted: 9 September 2018; Accepted: 10 December 2018; Published Online: 8 January 2019. We are grateful to Dr. Satoshi Inomata, Dr. Akihiro Fushimi, Dr. Kei Sato, and Dr. Yu Morino of NIES and Dr. Lijie Li and Dr. Michael Hoffmann of Caltech for valuable discussions. This work was supported in part by the JSPS KAKENHI (Grant Nos. 15H05328 and 15K12188). A.J.C. acknowledges support from the National Science Foundation, USA (Grant No. AGS-1744353).
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)15H05328
Japan Society for the Promotion of Science (JSPS)15K12188
Issue or Number:2
Record Number:CaltechAUTHORS:20190108-133606647
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Official Citation:Shinichi Enami, Shinnosuke Ishizuka, and Agustín J. Colussi. The Journal of Chemical Physics 2019 150:2. DOI: 10.1063/1.5055684
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92142
Deposited By: Tony Diaz
Deposited On:08 Jan 2019 21:44
Last Modified:16 Nov 2021 03:47

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