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Title: Dynamics of water confined in lyotropic liquid crystals: Molecular dynamics simulations of the dynamic structure factor

The properties of water under confinement are of practical and fundamental interest. Here in this work we study the properties of water in the self-assembled lyotropic phases of gemini surfactants with a focus on testing the standard analysis of quasi-elastic neutron scattering (QENS) experiments. In QENS experiments the dynamic structure factor is measured and fit to models to extract the translational diffusion constant, DT , and rotational relaxation time, τR. We test this procedure by using simulation results for the dynamic structure factor, extracting the dynamic parameters from the fit as is typically done in experiments, and comparing the values to those directly measured in the simulations. We find that the decoupling approximation, where the intermediate scattering function is assumed to be a product of translational and rotational contributions, is quite accurate. The jump-diffusion and isotropic rotation models, however, are not accurate when the degree of confinement is high. In particular, the exponential approximations for the intermediate scattering function fail for highly confined water and the values of DT and τR can differ from the measured value by as much as a factor of two. Other models have more fit parameters, however, and with the range of energies and wave-vectorsmore » accessible to QENS, the typical analysis appears to be the best choice. In the most confined lamellar phase, the dynamics are sufficiently slow that QENS does not access a large enough time scale and neutron spin echo measurements would be a valuable technique in addition to QENS.« less
Authors:
 [1] ;  [1]
  1. Univ. of Wisconsin, Madison, WI (United States). Theoretical Chemistry Inst. and Dept. of Chemistry
Publication Date:
Report Number(s):
DOE-UWMadison--46938-2nd product
Journal ID: ISSN 0021-9606; DE-FG02-13ER46938
Grant/Contract Number:
SC0010328; TG-CHE090065; CHE-0840494
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 8; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE quasielastic neutron scattering; QENS; lyotropic; double gyroid; decoupling approximation
OSTI Identifier:
1341620
Alternate Identifier(s):
OSTI ID: 1341620