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A fundamental understanding of confined water is crucial for developing selective ion transport and water purification membranes, yet the roles of nanopore geometry and functionality on confined water dynamics remain unresolved. We report the synthesis of perdeuterated ionic alkylsulfonate amphiphiles and their water-induced self-assembly into lyotropic liquid crystal (LLC) mesophases with well-defined, convex, sulfonate-lined nanopores. Quasielastic neutron scattering (QENS) measurements demonstrate that the water self-diffusion coefficients within these sulfonate-lined convex nanopores depend on the hydration level and amphiphile counterion identity (H +, K +, NMe 4 +). The consistency of the observed counterion-dependent water dynamics trends with those of carboxylate LLCs is rationalized on the basis of similarities in the counterion spatial distributions in the water-filled channels, which we deduce from electron density maps derived from small-angle X-ray scattering (SAXS) analyses. These findings indicate that water diffusion is systematically faster in sulfonate-lined nanopores as compared to carboxylate-lined pores due to weaker water interactions with the softer and more hydrophobic-SO 3 - functionalities. These molecular-level insights into the relationships between convex pore wall chemical functionalities, hydrated counterions, and confined water diffusion may inform future development of new nanoporous media.
Bibliographical noteFunding Information:
We gratefully acknowledge financial support for the experimental data acquisition portions of this work from the U.S. Department of Energy Basic Energy Sciences (DOE BES) Grant DE-SC0010328 (S.K. and M.K.M.), and support from National Science Foundation grant NSF-1608115 (A.J. and G.L.J) for the data analysis portions. G.L.J. also acknowledges a National Defense Science and Engineering Graduate (NDSEG) Fellowship from the U.S. Department of Defense. Synchrotron SAXS analyses were conducted at Sector 12 of the Advanced Photon Source at Argonne National Laboratory, which is supported through the U.S. DOE Contract DE-AC02-06CH11357 under GUP-45013 and GUP-48102. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Portions of this work were also carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program under Award Number DMR-1420013. Research reported in this publication was supported by the Office of the Director, National Institutes of Health under Award Number S10OD011952. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We thank Rick Goyette for logistical support during our BASIS measurement and Dr. Jose M. Borreguero for help with the MANTID program. We are also grateful to Prof. Arun Yethiraj, Dr. Sriteja Mantha, and Dr. Kenneth W. Herwig for helpful discussions regarding confined water dynamics.
Copyright © 2020 American Chemical Society.
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 6
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, U.S. Gov't, Non-P.H.S.