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

Journal Article · · ACS Applied Materials and Interfaces
 [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
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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.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Univ. of Pennsylvania, Philadelphia, PA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF); Simons Foundation (United States)
Grant/Contract Number:
AC52-07NA27344; DMR-1120901; DMR-1410253; DMR12-62047
OSTI ID:
1465270
Report Number(s):
LLNL-JRNL-747546; 932396
Journal Information:
ACS Applied Materials and Interfaces, Vol. 8, Issue 19; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 19 works
Citation information provided by
Web of Science

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Cited By (7)

Electrodynamic-contact-line-lithography with nematic liquid crystals for template-less E-writing of mesopatterns on soft surfaces journal January 2019
Light Robots: Bridging the Gap between Microrobotics and Photomechanics in Soft Materials journal October 2017
Advances in Cell Scaffolds for Tissue Engineering: The Value of Liquid Crystalline Elastomers journal May 2018
Bio-inspired liquid crystal actuator materials journal January 2019
Functional liquid crystalline particles and beyond journal June 2019
Reconfigurable topological photonic crystal journal February 2018
Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB journal May 2018

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
actuator
liquid crystal elastomer
monodomain
soft lithography
surface chemistry