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Title: Dynamics of Water in Gemini Surfactant-Based Lyotropic Liquid Crystals

Abstract

The dynamics of water confined to nanometer-sized domains is important in a variety of applications ranging from proton exchange membranes to crowding effects in biophysics. In this work we study the dynamics of water in gemini surfactant-based lyotropic liquid crystals (LLCs) using molecular dynamics simulations. These systems have well characterized morphologies, e.g., hexagonal, gyroid, and lamellar, and the surfaces of the confining regions can be controlled by modifying the headgroup of the surfactants. This allows one to study the effect of topology, functionalization, and interfacial curvature on the dynamics of confined water. Through analysis of the translational diffusion and rotational relaxation we conclude that the hydration level and resulting confinement lengthscale is the predominate determiner of the rates of water dynamics, and other effects, namely surface functionality and curvature, are largely secondary. In conclusion, this novel analysis of the water dynamics in these LLC systems provides an important comparison for previous studies of water dynamics in lipid bilayers and reverse micelles.

Authors:
 [1];  [1]; ORCiD logo [1]
  1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1341623
Report Number(s):
DOE-UWMadison-46938-5th product
Journal ID: ISSN 1520-6106; DE-FG02-13ER46938
Grant/Contract Number:
SC0010328; CHE-0840494
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
Journal Volume: 120; Journal Issue: 41; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; water dynamics; nanconfinement; lyotropic; liquid crystal

Citation Formats

McDaniel, Jesse G., Mantha, Sriteja, and Yethiraj, Arun. Dynamics of Water in Gemini Surfactant-Based Lyotropic Liquid Crystals. United States: N. p., 2016. Web. doi:10.1021/acs.jpcb.6b08087.
McDaniel, Jesse G., Mantha, Sriteja, & Yethiraj, Arun. Dynamics of Water in Gemini Surfactant-Based Lyotropic Liquid Crystals. United States. doi:10.1021/acs.jpcb.6b08087.
McDaniel, Jesse G., Mantha, Sriteja, and Yethiraj, Arun. Mon . "Dynamics of Water in Gemini Surfactant-Based Lyotropic Liquid Crystals". United States. doi:10.1021/acs.jpcb.6b08087. https://www.osti.gov/servlets/purl/1341623.
@article{osti_1341623,
title = {Dynamics of Water in Gemini Surfactant-Based Lyotropic Liquid Crystals},
author = {McDaniel, Jesse G. and Mantha, Sriteja and Yethiraj, Arun},
abstractNote = {The dynamics of water confined to nanometer-sized domains is important in a variety of applications ranging from proton exchange membranes to crowding effects in biophysics. In this work we study the dynamics of water in gemini surfactant-based lyotropic liquid crystals (LLCs) using molecular dynamics simulations. These systems have well characterized morphologies, e.g., hexagonal, gyroid, and lamellar, and the surfaces of the confining regions can be controlled by modifying the headgroup of the surfactants. This allows one to study the effect of topology, functionalization, and interfacial curvature on the dynamics of confined water. Through analysis of the translational diffusion and rotational relaxation we conclude that the hydration level and resulting confinement lengthscale is the predominate determiner of the rates of water dynamics, and other effects, namely surface functionality and curvature, are largely secondary. In conclusion, this novel analysis of the water dynamics in these LLC systems provides an important comparison for previous studies of water dynamics in lipid bilayers and reverse micelles.},
doi = {10.1021/acs.jpcb.6b08087},
journal = {Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry},
number = 41,
volume = 120,
place = {United States},
year = {Mon Sep 26 00:00:00 EDT 2016},
month = {Mon Sep 26 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Citation Metrics:
Cited by: 4works
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  • Cited by 2
  • 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, D T , and rotational relaxation time, τ R. 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 comparingmore » 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 D T and τ R 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-vectors 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
  • 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, D T , and rotational relaxation time, τ R. 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 comparingmore » 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 D T and τ R 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-vectors 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
  • Bilayers composed of lipid or surfactant molecules are central to biological membranes and lamellar lyotropic liquid crystalline (LLC) phases. Common to these systems are phases that exhibit either ordered or disordered packing of the hydrophobic tails. In this work, we study the impact of surfactant ordering, i.e., disordered L α and ordered L β LLC phases, on the dynamics of water and sodium ions in the lamellar phases of dicarboxylate gemini surfactants. We study the different phases at identical hydration levels by changing the length of the hydrophobic tails; surfactants with shorter tails form L α phases and those withmore » longer tails form L β phases. We find that the L α phases exhibit lower density and greater compressibility than the L β phases, with a hydration-dependent headgroup surface area. These structural differences significantly affect the relative dynamic properties of the phases, primarily the mobility of the surfactant molecules tangential to the bilayer surface, as well as the rates of water and ion diffusion. We find ~20–50% faster water diffusion in the L α phases compared to the L β phases, with the differences most pronounced at low hydration. This coupling between water dynamics and surfactant mobility is verified using additional simulations in which the surfactant tails are frozen. Our study indicates that gemini surfactant LLCs provide an important prototypical system for characterizing properties shared with more complex biological lipid membranes.« less