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. 2021 Oct 14;26(20):6193.
doi: 10.3390/molecules26206193.

Effect of Crosslinkers on Optical and Mechanical Behavior of Chiral Nematic Liquid Crystal Elastomers

Kyosun Ku  1 , Kyohei Hisano  1 , Kyoko Yuasa  1 , Tomoki Shigeyama  1 , Norihisa Akamatsu  2 , Atsushi Shishido  2 , Osamu Tsutsumi  1
Affiliations

Effect of Crosslinkers on Optical and Mechanical Behavior of Chiral Nematic Liquid Crystal Elastomers

Kyosun Ku et al. Molecules. .

Abstract

Chiral nematic (N*) liquid crystal elastomers (LCEs) are suitable for fabricating stimuli-responsive materials. As crosslinkers considerably affect the N*LCE network, we investigated the effects of crosslinking units on the physical properties of N*LCEs. The N*LCEs were synthesized with different types of crosslinkers, and the relationship between the N*LC polymeric system and the crosslinking unit was investigated. The N*LCEs emit color by selective reflection, in which the color changes in response to mechanical deformation. The LC-type crosslinker decreases the helical twisting power of the N*LCE by increasing the total molar ratio of the mesogenic compound. The N*LCE exhibits mechano-responsive color changes by coupling the N*LC orientation and the polymer network, where the N*LCEs exhibit different degrees of pitch variation depending on the crosslinker. Moreover, the LC-type crosslinker increases the Young's modulus of N*LCEs, and the long methylene chains increase the breaking strain. An analysis of experimental results verified the effect of the crosslinkers, providing a design rationale for N*LCE materials in mechano-optical sensor applications.

Keywords: chiral nematic liquid crystal elastomer; crosslinkers; mechano-optical sensor; selective reflection.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Chemical structures of the compounds used in the synthesis of N*LCEs.
Figure 1
Figure 1
POM images of N*LC samples before and after photopolymerization: (a) E-A6 before photopolymerization (as a representative example); (b) E-A6 after photopolymerization; (c) E-A10 after photopolymerization; (d) E-RM82 after photopolymerization.
Figure 2
Figure 2
DSC thermograms of N*LCEs on the second scanning cycles from −10 °C to 120 °C: (a) E-A6, (b) E-A10, and (c) E-RM82. The scanning rate was 10 °C min−1.
Figure 3
Figure 3
(a) Photographs and (b) normalized reflectance spectra of E-A6, E-A10, and E-RM82.
Figure 4
Figure 4
(a) Photographs and (b) normalized reflectance spectra of E-RM82 and E-HFA.
Figure 5
Figure 5
(a) Reflectance spectra of E-A6 and E-RM82 under tensile strain of 0% (solid line) and 45% (dashed line). (b) Stress–strain curves of the N*LCEs of E-A6, E-A10, and E-RM82. The strain was varied at a rate of 2 mm min−1.
Figure 6
Figure 6
Schematic of the fabrication process for synthesizing N*LCEs.
See this image and copyright information in PMC

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