Ion-specific Confined Water Dynamics in Convex Nanopores of Gemini Surfactant Lyotropic Liquid Crystals

Journal Article · 25 September 2018 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI: https://doi.org/10.1021/acs.jpcb.8b05942 · OSTI ID:1473701

Jackson, Grayson L. ^[1]; Mantha, Sriteja ^[1]; Kim, Sung A. ^[2]; Diallo, Souleymane O. ^[3]; Herwig, Kenneth W. ^[4]; Yethiraj, Arun ^[1]; Mahanthappa, Mahesh K. ^[5]

---

1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemistry
2. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Science Division
5. Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemistry; Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science

The impact of pore geometry and functionality on the dynamics of water nanoconfined in porous media are the subject of some debate. Here, we report the synthesis and small-angle X-ray scattering (SAXS) characterization of a series of perdeuterated gemini surfactant lyotropic liquid crystals (LLCs), in which convex, water-filled nanopores of well-defined dimensions are lined with carboxylate functionalities. Quasielastic neutron scattering (QENS) measurements of the translational water dynamics in these dicarboxylate LLC nanopores as functions of the surfactant hydration state and the charge compensating counterion (Na⁺, K⁺, NMe₄⁺) reveal that the measured dynamics depend primarily on surfactant hydration, with an unexpected counterion dependence that varies with hydration number. We rationalize these trends in terms of a balance between counterion-water attractions and the nanopore volume excluded by the counterions. On the basis of electron density maps derived from SAXS analyses of these LLCs, we directly show that the volume excluded by the counterions depends on both their size and spatial distribution in the water-filled channels. The translational water dynamics in the convex pores of these LLCs are also slower than those reported in the concave pores of AOT reverse micelles, implying that water dynamics also depend on the nanopore curvature.

• Research Organization: Univ. of Minnesota, Minneapolis, MN (United States); Argonne National Laboratory (ANL), Argonne, IL (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); US Dept. of Defense (DOD); National Science Foundation (NSF); National Institutes of Health (NIH)
• Grant/Contract Number: SC0010328; AC02-06CH11357; CHE-9974839; CHE-1048642; DMR-0832760; DMR-1121288; DMR-1420013; S10OD011952
• OSTI ID: 1473701
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 122, Issue 43; ISSN 1520-6106
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE