eprintid: 1530789 rev_number: 35 eprint_status: archive userid: 608 dir: disk0/01/53/07/89 datestamp: 2016-12-06 15:37:29 lastmod: 2021-11-07 00:12:29 status_changed: 2017-03-15 13:08:57 type: article metadata_visibility: show creators_name: Loganathan, N creators_name: Yazaydin, AO creators_name: Bowers, GM creators_name: Kalinichev, AG creators_name: Kirkpatrick, RJ title: Structure, Energetics, and Dynamics of Cs+ and H2O in Hectorite: Molecular Dynamics Simulations with an Unconstrained Substrate Surface ispublished: pub divisions: UCL divisions: B04 divisions: C05 divisions: F43 keywords: Science & Technology, Physical Sciences, Technology, Chemistry, Physical, Nanoscience & Nanotechnology, Materials Science, Multidisciplinary, Chemistry, Science & Technology - Other Topics, Materials Science, Crystal Structure Refinement, Elastic Neutron-scattering, Monte-carlo-simulation, Natural Organic-matter, Dense Clay Sediments, Level Nuclear-waste, Water-structure, Interlayer Structure, Na-hectorite, Exchangeable Cations note: Copyright © 2016 American Chemical Society abstract: Classical molecular dynamics simulations were performed for the smectite clay hectorite with charge-balancing Cs+ cations using a newly developed structural model with a disordered distribution of Li/Mg substitutions in the octahedral sheet and the fully flexible CLAYFF force field. Calculations for systems with interlayer galleries containing 0–19 H2O/Cs+ suggest that the monolayer hydrate is the only stable state at all relative humidities at ambient pressure and temperature, in agreement with experimental results and previous molecular calculations. The basal spacing of this structure is also in good agreement with experimental values. In contrast to previous molecular modeling results, however, the new simulations show that interlayer Cs+ occurs on 2 different inner sphere adsorption sites: above the center of ditrigonal cavities and above Si tetrahedra. Unlike previous simulations, which employed a rigid clay model and fixed orientations of the structural −OH groups, the present results are obtained for an unconstrained clay substrate structure, where the structural −OH groups are able to assume various orientations, including being nearly parallel to the clay layers. This flexibility allows the Cs+ ions to approach the surface more closely above the centers of the hexagonal rings. In this structural arrangement, Cs+ ions are not hydrated by the H2O molecules which share the same interlayer plane, but rather by the H2O molecules coordinated to the opposite surface. In contrast, on the external basal surface, a significant fraction of H2O molecules are adsorbed above the centers of ditrigonal cavities adjacent to adsorbed Cs+ ions. For these H2O molecules, both HH2O atoms coordinate and H-bond to Ob surface oxygen atoms. The mean residence times for the Cs+–H2O, Cs+–Ob, and H2O–Ob coordination pairs show that Cs+ ions are more strongly coordinated with Ob atoms than H2O molecules. This result is the opposite of the behavior in Ca-hectorite, due to the much smaller hydration energy of Cs+ compared to that of Ca2+. date: 2016-05-19 date_type: published publisher: AMER CHEMICAL SOC official_url: http://dx.doi.org/10.1021/acs.jpcc.6b01016 oa_status: green full_text_type: other language: eng primo: open primo_central: open_green article_type_text: Article verified: verified_manual elements_id: 1153533 doi: 10.1021/acs.jpcc.6b01016 lyricists_name: Yazaydin, Ahmet lyricists_id: AOYAZ19 actors_name: Yazaydin, Ahmet actors_id: AOYAZ19 actors_role: owner full_text_status: public publication: Journal of Physical Chemistry C volume: 120 number: 19 pagerange: 10298-10310 pages: 13 issn: 1932-7447 citation: Loganathan, N; Yazaydin, AO; Bowers, GM; Kalinichev, AG; Kirkpatrick, RJ; (2016) Structure, Energetics, and Dynamics of Cs+ and H2O in Hectorite: Molecular Dynamics Simulations with an Unconstrained Substrate Surface. Journal of Physical Chemistry C , 120 (19) pp. 10298-10310. 10.1021/acs.jpcc.6b01016 <https://doi.org/10.1021/acs.jpcc.6b01016>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/1530789/1/Yazaydin_Cs-Hectorite%20revised-Final.pdf