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

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6193
Author(s):  
Kyosun Ku ◽  
Kyohei Hisano ◽  
Kyoko Yuasa ◽  
Tomoki Shigeyama ◽  
Norihisa Akamatsu ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Polymer Network ◽  
Molar Ratio ◽  
Stimuli Responsive ◽  
Breaking Strain ◽  
Responsive Materials ◽  
Sensor Applications ◽  
Color Changes ◽  
Chiral Nematic ◽  
Liquid Crystal Elastomers

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.

scholarly journals Environmentally Stable Chiral-Nematic Liquid-Crystal Elastomers with Mechano-Optical Properties

2021 ◽  
Vol 11 (11) ◽  
pp. 5037
Author(s):  
Kyosun Ku ◽  
Kyohei Hisano ◽  
Seiya Kimura ◽  
Tomoki Shigeyama ◽  
Norihisa Akamatsu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Optical Sensors ◽  
Polymer Network ◽  
Sensor Applications ◽  
Chiral Nematic ◽  
Cross Links ◽  
Responsive Behavior ◽  
Liquid Crystal Elastomers

Chiral-nematic liquid crystal (N* LC) elastomers exhibit mechano-optical responsive behavior. However, practical sensor applications have been limited by the intrinsic sensitivity of N* LC elastomers to environmental conditions, such as temperature. Although densely cross-linked LC network polymers exhibit high thermal stability, they are not proper for the mechanical sensor due to high glass transition temperatures and low flexibility. To overcome these issues, we focused on enhancing thermal stability by introducing noncovalent cross-linking sites via intermolecular interactions between LC molecules bonded to the polymer network. N* LC elastomers with a cyanobiphenyl derivative as a side-chain mesogen exhibited mechano-optical responsive behavior, with a hypsochromic shift of the reflection peak wavelength under an applied tensile strain and quick shape and color recovery owing to high elasticity. Notably, the N* LC elastomers showed high resistance to harsh environments, including high temperatures and various solvents. Interactions, such as π–π stacking and dipole–dipole interactions, between the cyanobiphenyl units can act as weak cross-links, thus improving the thermal stability of the LC phase without affecting the mechano-optical response. Thus, these N* LC elastomers have great potential for the realization of practical mechano-optical sensors.

scholarly journals Shape memory polymer network with thermally distinct elasticity and plasticity

2016 ◽  
Vol 2 (1) ◽  
pp. e1501297 ◽  
Author(s):  
Qian Zhao ◽  
Weike Zou ◽  
Yingwu Luo ◽  
Tao Xie
Keyword(s):  
Shape Memory ◽  
Molecular Design ◽  
Shape Change ◽  
Shape Memory Polymer ◽  
Polymer Network ◽  
Stimuli Responsive ◽  
Responsive Materials ◽  
Device Applications ◽  
Temperature Ranges ◽  
Rational Molecular Design

Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices.

scholarly journals Degradation-Induced Actuation in Oxidation-Responsive Liquid Crystal Elastomers

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 420 ◽  
Author(s):  
Mahjabeen Javed ◽  
Seelay Tasmim ◽  
Mustafa K. Abdelrahman ◽  
Cedric P. Ambulo ◽  
Taylor H. Ware
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Polymer Network ◽  
Orthogonal Expansion ◽  
Aqueous Environment ◽  
Wide Range ◽  
Anisotropic Mechanical Properties ◽  
Liquid Crystal Elastomers ◽  
Shape Changes

Stimuli-responsive materials that exhibit a mechanical response to specific biological conditions are of considerable interest for responsive, implantable medical devices. Herein, we report the synthesis, processing and characterization of oxidation-responsive liquid crystal elastomers that demonstrate programmable shape changes in response to reactive oxygen species. Direct ink writing (DIW) is used to fabricate Liquid Crystal Elastomers (LCEs) with programmed molecular orientation and anisotropic mechanical properties. LCE structures were immersed in different media (oxidative, basic and saline) at body temperature to measure in vitro degradation. Oxidation-sensitive hydrophobic thioether linkages transition to hydrophilic sulfoxide and sulfone groups. The introduction of these polar moieties brings about anisotropic swelling of the polymer network in an aqueous environment, inducing complex shape changes. 3D-printed uniaxial strips exhibit 8% contraction along the nematic director and 16% orthogonal expansion in oxidative media, while printed LCEs azimuthally deform into cones 19 times their original thickness. Ultimately, these LCEs degrade completely. In contrast, LCEs subjected to basic and saline solutions showed no apparent response. These oxidation-responsive LCEs with programmable shape changes may enable a wide range of applications in target specific drug delivery systems and other diagnostic and therapeutic tools.

Robotic surfaces with reversible, spatiotemporal control for shape morphing and object manipulation

2021 ◽  
Vol 6 (53) ◽  
pp. eabf5116
Author(s):  
Ke Liu ◽  
Felix Hacker ◽  
Chiara Daraio
Keyword(s):  
Stimuli Responsive ◽  
Mechanical Stiffness ◽  
Responsive Materials ◽  
Shape Morphing ◽  
Deformation Response ◽  
Control Scheme ◽  
Out Of Plane ◽  
Passive Network ◽  
Liquid Crystal Elastomers ◽  
Layered Design

Continuous and controlled shape morphing is essential for soft machines to conform, grasp, and move while interacting safely with their surroundings. Shape morphing can be achieved with two-dimensional (2D) sheets that reconfigure into target 3D geometries, for example, using stimuli-responsive materials. However, most existing solutions lack the ability to reprogram their shape, face limitations on attainable geometries, or have insufficient mechanical stiffness to manipulate objects. Here, we develop a soft, robotic surface that allows for large, reprogrammable, and pliable shape morphing into smooth 3D geometries. The robotic surface consists of a layered design composed of two active networks serving as artificial muscles, one passive network serving as a skeleton, and cover scales serving as an artificial skin. The active network consists of a grid of strips made of heat-responsive liquid crystal elastomers (LCEs) containing stretchable heating coils. The magnitude and speed of contraction of the LCEs can be controlled by varying the input electric currents. The 1D contraction of the LCE strips activates in-plane and out-of-plane deformations; these deformations are both necessary to transform a flat surface into arbitrary 3D geometries. We characterize the fundamental deformation response of the layers and derive a control scheme for actuation. We demonstrate that the robotic surface provides sufficient mechanical stiffness and stability to manipulate other objects. This approach has potential to address the needs of a range of applications beyond shape changes, such as human-robot interactions and reconfigurable electronics.

Artificial muscles based on liquid crystal elastomers

2006 ◽  
Vol 364 (1847) ◽  
pp. 2763-2777 ◽  
Author(s):  
Min-Hui Li ◽  
Patrick Keller
Keyword(s):  
Liquid Crystal ◽  
Main Chain ◽  
Uv Light ◽  
Shape Change ◽  
Artificial Muscle ◽  
Isotropic Phase ◽  
Artificial Muscles ◽  
Stimuli Responsive ◽  
Liquid Crystal Elastomers ◽  
The Individual

This paper presents our results on liquid crystal (LC) elastomers as artificial muscle, based on the ideas proposed by de Gennes. In the theoretical model, the material consists of a repeated series of main-chain nematic LC polymer blocks, N, and conventional rubber blocks, R, based on the lamellar phase of a triblock copolymer RNR. The motor for the contraction is the reversible macromolecular shape change of the chain, from stretched to spherical, that occurs at the nematic-to-isotropic phase transition in the main-chain nematic LC polymers. We first developed a new kind of muscle-like material based on a network of side-on nematic LC homopolymers. Side-on LC polymers were used instead of main-chain LC polymers for synthetic reasons. The first example of these materials was thermo-responsive, with a typical contraction of around 35–45% and a generated force of around 210 kPa. Subsequently, a photo-responsive material was developed, with a fast photochemically induced contraction of around 20%, triggered by UV light. We then succeeded in preparing a thermo-responsive artificial muscle, RNR, with lamellar structure, using a side-on nematic LC polymer as N block. Micrometre-sized artificial muscles were also prepared. This paper illustrates the bottom-up design of stimuli-responsive materials, in which the overall material response reflects the individual macromolecular response, using LC polymer as building block.

High strain actuation liquid crystal elastomers via modulation of mesophase structure

Soft Matter ◽  
2017 ◽  
Vol 13 (41) ◽  
pp. 7537-7547 ◽  
Author(s):  
Mohand O. Saed ◽  
Ross H. Volpe ◽  
Nicholas A. Traugutt ◽  
Rayshan Visvanathan ◽  
Noel A. Clark ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
High Strain ◽  
Stimuli Responsive ◽  
Critical Aspect ◽  
Liquid Crystal Elastomers

Control of the mesophase in liquid crystalline elastomers (LCEs) is a critical aspect in harnessing their unique stimuli-responsive properties.

scholarly journals Stimuli-Responsive Materials Based on Interpenetrating Polymer Liquid Crystal Hydrogels

2015 ◽  
Vol 25 (22) ◽  
pp. 3314-3320 ◽  
Author(s):  
Jelle E. Stumpel ◽  
Elda Renedo Gil ◽  
Anne B. Spoelstra ◽  
Cees W. M. Bastiaansen ◽  
Dirk J. Broer ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Stimuli Responsive ◽  
Responsive Materials ◽  
Polymer Liquid ◽  
Polymer Liquid Crystal

Sample preparation affects the nematic–isotropic transition in liquid crystal elastomers: insights from molecular simulation

Soft Matter ◽  
2018 ◽  
Vol 14 (8) ◽  
pp. 1408-1416 ◽  
Author(s):  
Gregor Skačej
Keyword(s):  
Liquid Crystal ◽  
Sample Preparation ◽  
Molecular Simulation ◽  
Polymer Network ◽  
Molecular Simulations ◽  
Liquid Crystal Elastomers

Molecular simulations elucidate how sample preparation—polymer network irregularity and swelling—affects the nematic–isotropic transition in liquid crystal elastomers.

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