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Title: Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes

Abstract

Controlling the orientation of liquid crystal (LC) molecules towards contacting surfaces is a crucial requirement for the development of LC displays and passive electro-optical devices. Up to now, research has been focused on photo-responses of a LC azobenzene polymer system to obtain either planar or homeotropic orientation of LCs. It remains a challenge, however, to tune the polar angle of LC molecules on the solid surface and gain more insights about the polymer chain conformation extending in LC medium. Here, we deposit a liquid crystalline side chain polymer brush, poly(6-(4-methoxy-azobenzene-4'-oxy)hexyl methacrylate) (PMMAZO), onto the solid surface with film thickness varying between ~3 nm and 13 nm; therefore, the grafting density of the brush layer ranges from 0.0219 to 0.0924 chains per nm 2. When LCs are confined in hybrid cells with a top surface eliciting uniform homeotropic anchoring and a bottom surface covered by the PMMAZO brush, the out-of-plane polar angle of 4-pentyl-4'-cyanobiphenyl (5CB) on the brush layer gradually changes from ~0° to ~62° by simply increasing the grafting brush density. The surface forces apparatus (SFA) measurement is used to determine 5CB as a good solvent for the PMMAZO brush and understand the relationship between the chain conformation in 5CBmore » and the anchoring behavior of LC molecules on the polymer brush layer. Here, for high grafting density, the polymer chain in 5CB extends significantly away from the substrate, making the side chain mesogens on average almost parallel to the substrate; for the low-density case, the main chain extends in the narrow region around the surface for aligning the mesogens perpendicular to the substrate.« less

Authors:
ORCiD logo [1];  [2];  [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [3]; ORCiD logo [4]
  1. Univ. of Chicago, Chicago, IL (United States)
  2. Univ. of Chicago, Chicago, IL (United States); Tohoku Univ. (Japan)
  3. Tohoku Univ. (Japan)
  4. Univ. of Chicago, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; USDOE
OSTI Identifier:
1557668
Alternate Identifier(s):
OSTI ID: 1462445
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Accepted Manuscript
Journal Name:
Soft Matter
Additional Journal Information:
Journal Volume: 14; Journal Issue: 37; Journal ID: ISSN 1744-683X
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Li, Xiao, Yanagimachi, Takuya, Bishop, Camille, Smith, Coleman, Dolejsi, Moshe, Xie, Helou, Kurihara, Kazue, and Nealey, Paul F. Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes. United States: N. p., 2018. Web. doi:10.1039/c8sm00991k.
Li, Xiao, Yanagimachi, Takuya, Bishop, Camille, Smith, Coleman, Dolejsi, Moshe, Xie, Helou, Kurihara, Kazue, & Nealey, Paul F. Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes. United States. doi:10.1039/c8sm00991k.
Li, Xiao, Yanagimachi, Takuya, Bishop, Camille, Smith, Coleman, Dolejsi, Moshe, Xie, Helou, Kurihara, Kazue, and Nealey, Paul F. Wed . "Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes". United States. doi:10.1039/c8sm00991k. https://www.osti.gov/servlets/purl/1557668.
@article{osti_1557668,
title = {Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes},
author = {Li, Xiao and Yanagimachi, Takuya and Bishop, Camille and Smith, Coleman and Dolejsi, Moshe and Xie, Helou and Kurihara, Kazue and Nealey, Paul F.},
abstractNote = {Controlling the orientation of liquid crystal (LC) molecules towards contacting surfaces is a crucial requirement for the development of LC displays and passive electro-optical devices. Up to now, research has been focused on photo-responses of a LC azobenzene polymer system to obtain either planar or homeotropic orientation of LCs. It remains a challenge, however, to tune the polar angle of LC molecules on the solid surface and gain more insights about the polymer chain conformation extending in LC medium. Here, we deposit a liquid crystalline side chain polymer brush, poly(6-(4-methoxy-azobenzene-4'-oxy)hexyl methacrylate) (PMMAZO), onto the solid surface with film thickness varying between ~3 nm and 13 nm; therefore, the grafting density of the brush layer ranges from 0.0219 to 0.0924 chains per nm2. When LCs are confined in hybrid cells with a top surface eliciting uniform homeotropic anchoring and a bottom surface covered by the PMMAZO brush, the out-of-plane polar angle of 4-pentyl-4'-cyanobiphenyl (5CB) on the brush layer gradually changes from ~0° to ~62° by simply increasing the grafting brush density. The surface forces apparatus (SFA) measurement is used to determine 5CB as a good solvent for the PMMAZO brush and understand the relationship between the chain conformation in 5CB and the anchoring behavior of LC molecules on the polymer brush layer. Here, for high grafting density, the polymer chain in 5CB extends significantly away from the substrate, making the side chain mesogens on average almost parallel to the substrate; for the low-density case, the main chain extends in the narrow region around the surface for aligning the mesogens perpendicular to the substrate.},
doi = {10.1039/c8sm00991k},
journal = {Soft Matter},
number = 37,
volume = 14,
place = {United States},
year = {2018},
month = {8}
}

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