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Title: In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals

Abstract

Experiments on confined droplets of the nematic liquid crystal 5CB have questioned long-established bounds imposed on the elastic free energy of nematic systems. This elasticity, which derives from molecular alignment within nematic systems, is quantified through a set of moduli which can be difficult to measure experimentally and, in some cases, can only be probed indirectly. This is particularly true of the surfacelike saddle-splay elastic term, for which the available experimental data indicate values on the cusp of stability, often with large uncertainties. Here, we demonstrate that all nematic elastic moduli, including the saddle-splay elastic constant k 24, may be calculated directly from atomistic molecular simulations. Importantly, results obtained through in silico measurements of the 5CB elastic properties demonstrate unambiguously that saddle-splay elasticity alone is unable to describe the observed confined morphologies.

Authors:
 [1];  [2];  [1]
  1. Univ. of Notre Dame, IN (United States). Dept. of Chemical and Biomolecular Engineering
  2. Univ. of Chicago, IL (United States). Inst. for Molecular Engineering; Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
U.S. Department of Defense (DOD) - Department of the Army; National Science Foundation (NSF); USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division - Midwest Integrated Center for Computational Materials (MICCoM); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1459901
Alternate Identifier(s):
OSTI ID: 1425231
Grant/Contract Number:  
AC02-06CH11357; MURI W911NF-15-1-0568
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 10; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Sidky, Hythem, de Pablo, Juan J., and Whitmer, Jonathan K. In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.120.107801.
Sidky, Hythem, de Pablo, Juan J., & Whitmer, Jonathan K. In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals. United States. doi:10.1103/PhysRevLett.120.107801.
Sidky, Hythem, de Pablo, Juan J., and Whitmer, Jonathan K. Fri . "In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals". United States. doi:10.1103/PhysRevLett.120.107801. https://www.osti.gov/servlets/purl/1459901.
@article{osti_1459901,
title = {In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals},
author = {Sidky, Hythem and de Pablo, Juan J. and Whitmer, Jonathan K.},
abstractNote = {Experiments on confined droplets of the nematic liquid crystal 5CB have questioned long-established bounds imposed on the elastic free energy of nematic systems. This elasticity, which derives from molecular alignment within nematic systems, is quantified through a set of moduli which can be difficult to measure experimentally and, in some cases, can only be probed indirectly. This is particularly true of the surfacelike saddle-splay elastic term, for which the available experimental data indicate values on the cusp of stability, often with large uncertainties. Here, we demonstrate that all nematic elastic moduli, including the saddle-splay elastic constant k24, may be calculated directly from atomistic molecular simulations. Importantly, results obtained through in silico measurements of the 5CB elastic properties demonstrate unambiguously that saddle-splay elasticity alone is unable to describe the observed confined morphologies.},
doi = {10.1103/PhysRevLett.120.107801},
journal = {Physical Review Letters},
number = 10,
volume = 120,
place = {United States},
year = {2018},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 2 works
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Figures / Tables:

Figure 1 Figure 1: Top row shows idealized bulk elastic modes (a) splay (b) twist and (c) bend, which can be directly probed in experiment. Bottom row shows the 5CB molecule (d) and cylindrical twist deformations, which rely on the saddle-splay elastic constant k24, in stable (e) and unstable (f) configurations undermore » conditions of degenerate planar anchoring representative of the commonly studied 5CB–water interface. Saddle-splay is not directly measurable through experiment but can be inferred indirectly. The positive-definiteness of the elastic free energy expressed through the Ericksen bound k22−k24 ≥ 0 is thought to be violated for 5CB, though experiments are not conclusive.« less

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