中文版 | English
Title

Direct Observation of Biaxial Nematic Order in Auxetic Liquid Crystal Elastomers

Author
Corresponding AuthorRaistrick, Thomas
Publication Years
2023-01
DOI
Source Title
EISSN
1996-1944
Volume16
Abstract
Auxetic materials exhibit a negative Poisson’s ratio, i.e., they become thicker rather than thinner in at least one dimension when strained. Recently, a nematic liquid crystal elastomer (LCE) was shown to be the first synthetic auxetic material at a molecular level. Understanding the mechanism of the auxetic response in LCEs is clearly important, and it has been suggested through detailed Raman scattering studies that it is related to the reduction of uniaxial order and emergence of biaxial order on strain. In this paper, we demonstrate direct observation of the biaxial order in an auxetic LCE under strain. We fabricated ~100 μm thick LCE strips with complementary geometries, exhibiting either planar or homeotropic alignment, in which the auxetic response is seen in the thickness or width of the sample, respectively. Polarized Raman scattering measurements on the planar sample show directly the reduction in the uniaxial order parameters on strain and suggest the emergence of biaxial order to mediate the auxetic response in the sample thickness. The homeotropic sample is studied via conoscopy, allowing direct observation of both the auxetic response in the width of the sample and increasing biaxiality in the LCE as it is strained. We verified that the mechanism of the auxetic response in auxetic LCEs is due to the emergence of the biaxial order and conclude such materials can be added to the small number of biaxial nematic systems that have been observed. Importantly, we also show that the mechanical Frèedericksz transition seen in some LCEs is consistent with a strain-induced transition from an optically positive to an optically negative biaxial system under strain, rather than a director rotation in a uniaxial system.
© 2022 by the authors.
Indexed By
EI ; SCI
Language
English
SUSTech Authorship
Others
Funding Project
This research was funded by the Engineering and Physical Sciences Research Council (EPSRC EP/V054724/1).
WOS Accession No
WOS:000908975500001
Publisher
EI Accession Number
20230213360275
EI Keywords
Elastomers ; Nematic liquid crystals ; Plastics
ESI Classification Code
Light/Optics:741.1 ; Polymer Products:817.1 ; Elastomers:818.2
Data Source
EV Compendex
Citation statistics
Cited Times [WOS]:0
Document TypeJournal Article
Identifierhttp://kc.sustech.edu.cn/handle/2SGJ60CL/519746
DepartmentDepartment of Electrical and Electronic Engineering
Affiliation
1.School of Physics and Astronomy, University of Leeds, Leeds; LS2 9JT, United Kingdom
2.Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Shenzhen; 518055, China
First Author AffilicationDepartment of Electrical and Electronic Engineering
Recommended Citation
GB/T 7714
Wang, Zhenming,Raistrick, Thomas,Street, Aidan,et al. Direct Observation of Biaxial Nematic Order in Auxetic Liquid Crystal Elastomers[J]. Materials,2023,16.
APA
Wang, Zhenming,Raistrick, Thomas,Street, Aidan,Reynolds, Matthew,Liu, Yanjun,&Gleeson, Helen F..(2023).Direct Observation of Biaxial Nematic Order in Auxetic Liquid Crystal Elastomers.Materials,16.
MLA
Wang, Zhenming,et al."Direct Observation of Biaxial Nematic Order in Auxetic Liquid Crystal Elastomers".Materials 16(2023).
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