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Title: Comparing Simulated and X-ray-measured Surface Structure: The Case of Ionic Liquids

Abstract

The surface-normal electron density profile of an ionic liquid, [bmim][PF{sub 6}], derived from x-ray reflectivity measurements, is compared with two independent molecular-dynamics simulations. It is shown that a meaningful comparison requires a detailed accounting for both thermal and nonthermal surface roughening effects. The former is due to thermally excited capillary waves, and the latter is due to the molecular zero-point motion and form. These quantities influence very significantly, but differently, the simulated and measured density profiles. Stripping off these effects from both types of profiles yields the intrinsic structure factor of the surface. The simulated intrinsic structure factors are found to deviate considerably from the measured one. The introduction of additional ad hoc surface roughness to the simulated profiles greatly reduces the deviation, however, no physical origin for this effect can be identified. The method employed in this study should prove useful for simulation-experiment comparisons of other liquid surfaces, provided they obey capillary-wave theory, as do almost all liquid surfaces studied to date by x-ray reflectivity.

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930581
Report Number(s):
BNL-80790-2008-JA
Journal ID: ISSN 0021-9606; JCPSA6; TRN: US200904%%601
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 175; Journal Issue: 17
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LIQUIDS; ORGANIC COMPOUNDS; SURFACE PROPERTIES; MORPHOLOGY; ELECTRON DENSITY; MOLECULAR DYNAMICS METHOD; ROUGHNESS; STRUCTURE FACTORS; national synchrotron light source

Citation Formats

Sloutskin ,E., Lynden-Bell, R., Balasubramanian, S., and Deutsch, M. Comparing Simulated and X-ray-measured Surface Structure: The Case of Ionic Liquids. United States: N. p., 2006. Web. doi:10.1063/1.2361289.
Sloutskin ,E., Lynden-Bell, R., Balasubramanian, S., & Deutsch, M. Comparing Simulated and X-ray-measured Surface Structure: The Case of Ionic Liquids. United States. doi:10.1063/1.2361289.
Sloutskin ,E., Lynden-Bell, R., Balasubramanian, S., and Deutsch, M. Sun . "Comparing Simulated and X-ray-measured Surface Structure: The Case of Ionic Liquids". United States. doi:10.1063/1.2361289.
@article{osti_930581,
title = {Comparing Simulated and X-ray-measured Surface Structure: The Case of Ionic Liquids},
author = {Sloutskin ,E. and Lynden-Bell, R. and Balasubramanian, S. and Deutsch, M.},
abstractNote = {The surface-normal electron density profile of an ionic liquid, [bmim][PF{sub 6}], derived from x-ray reflectivity measurements, is compared with two independent molecular-dynamics simulations. It is shown that a meaningful comparison requires a detailed accounting for both thermal and nonthermal surface roughening effects. The former is due to thermally excited capillary waves, and the latter is due to the molecular zero-point motion and form. These quantities influence very significantly, but differently, the simulated and measured density profiles. Stripping off these effects from both types of profiles yields the intrinsic structure factor of the surface. The simulated intrinsic structure factors are found to deviate considerably from the measured one. The introduction of additional ad hoc surface roughness to the simulated profiles greatly reduces the deviation, however, no physical origin for this effect can be identified. The method employed in this study should prove useful for simulation-experiment comparisons of other liquid surfaces, provided they obey capillary-wave theory, as do almost all liquid surfaces studied to date by x-ray reflectivity.},
doi = {10.1063/1.2361289},
journal = {Journal of Chemical Physics},
number = 17,
volume = 175,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}