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.
Highlights
Our results revealed that the low helical twisting power (HTP) value in the mesogenic crosslinker system is due to the larger molar ratio of mesogenic compounds
Crystalline-to-N*liquid crystals (LCs) phase transition temperature of the monomer mixtures were slightly decreased by increasing the methylene chain length in the crosslinking unit
Longer methylene chains in the crosslinker increased the breaking strain. This is reasonable because the N*liquid crystal elastomers (LCEs) have the same crosslinking density but different methylene chain lengths, in which the N*LCEs with longer methylene chain lengths deform over a wider range. These results provide the effect of a crosslinker in the mechano-optical actuation of N*LCE, indicating that mechanical properties such as stiffness and stretchability can be independently controlled by using a different crosslinker
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The periodic helical structure of an N*LC spontaneously self-assembles when an achiral LC is mixed with chiral moieties and/or a chiral LC is used [4,5]. This helix has a refractive-index distribution along the helical axis and exhibits selective reflection of circularly polarized light with the same handedness at a specific wavelength according to Bragg reflection [6,7]. The peak reflection wavelength (λpeak ) is related to the helical pitch (P) corresponding to the length of a
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