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Title: Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers

Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). In this paper, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau–de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by polarized optical microscopy, we observe monodomains of vertically aligned LCMs within the mold, in agreement with modeling. Finally, after curing and peeling off the mold, the resulting NLCE micropillars showed a relatively large and reversible radial strain (~30%) when heated above the nematic to isotropic transition temperature.
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [5] ;  [6] ;  [5] ;  [1]
  1. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering
  2. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Engineering Directorate
  3. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering. Dept. of Physics and Astronomy
  4. Harvard Univ., Cambridge, MA (United States). Paulson School of Engineering and Applied Sciences
  5. Johannes Gutenberg Univ. Mainz (Germany). Inst. of Organic Chemistry
  6. Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Physics and Astronomy
Publication Date:
Report Number(s):
LLNL-JRNL-747546
Journal ID: ISSN 1944-8244; 932396
Grant/Contract Number:
AC52-07NA27344; DMR-1120901; DMR-1410253; DMR12-62047
Type:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 8; Journal Issue: 19; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Pennsylvania, Philadelphia, PA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF); Simons Foundation (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; actuator; liquid crystal elastomer; monodomain; soft lithography; surface chemistry
OSTI Identifier:
1465270

Xia, Yu, Lee, Elaine, Hu, Hao, Gharbi, Mohamed Amine, Beller, Daniel A., Fleischmann, Eva-Kristina, Kamien, Randall D., Zentel, Rudolf, and Yang, Shu. Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers. United States: N. p., Web. doi:10.1021/acsami.6b02789.
Xia, Yu, Lee, Elaine, Hu, Hao, Gharbi, Mohamed Amine, Beller, Daniel A., Fleischmann, Eva-Kristina, Kamien, Randall D., Zentel, Rudolf, & Yang, Shu. Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers. United States. doi:10.1021/acsami.6b02789.
Xia, Yu, Lee, Elaine, Hu, Hao, Gharbi, Mohamed Amine, Beller, Daniel A., Fleischmann, Eva-Kristina, Kamien, Randall D., Zentel, Rudolf, and Yang, Shu. 2016. "Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers". United States. doi:10.1021/acsami.6b02789. https://www.osti.gov/servlets/purl/1465270.
@article{osti_1465270,
title = {Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers},
author = {Xia, Yu and Lee, Elaine and Hu, Hao and Gharbi, Mohamed Amine and Beller, Daniel A. and Fleischmann, Eva-Kristina and Kamien, Randall D. and Zentel, Rudolf and Yang, Shu},
abstractNote = {Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). In this paper, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau–de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by polarized optical microscopy, we observe monodomains of vertically aligned LCMs within the mold, in agreement with modeling. Finally, after curing and peeling off the mold, the resulting NLCE micropillars showed a relatively large and reversible radial strain (~30%) when heated above the nematic to isotropic transition temperature.},
doi = {10.1021/acsami.6b02789},
journal = {ACS Applied Materials and Interfaces},
number = 19,
volume = 8,
place = {United States},
year = {2016},
month = {5}
}