scholarly journals Photo-Mechanical Response Dynamics of Liquid Crystal Elastomer Linear Actuators

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2933
Author(s):  
Przemysław Grabowski ◽  
Jakub Haberko ◽  
Piotr Wasylczyk
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Nanometer Scale ◽  
Response Dynamics ◽  
Responsive Materials ◽  
Liquid Crystal Elastomer ◽  
Power Pulse ◽  
Liquid Crystal Elastomers ◽  
Further Development ◽  
Simple Behavior

With continuous miniaturization of many technologies, robotics seems to be lagging behind. While the semiconductor technologies operate confidently at the nanometer scale and micro-mechanics of simple structures (MEMS) in micrometers, autonomous devices are struggling to break the centimeter barrier and have hardly colonized smaller scales. One way towards miniaturization of robots involves remotely powered, light-driven soft mechanisms based on photo-responsive materials, such as liquid crystal elastomers (LCEs). While several simple devices have been demonstrated with contracting, bending, twisting, or other, more complex LCE actuators, only their simple behavior in response to light has been studied. Here we characterize the photo-mechanical response of a linear light-driven LCE actuator by measuring its response to laser beams with varying power, pulse duration, pulse energy, and the energy spatial distribution. Light absorption decrease in the actuator over time is also measured. These results are at the foundation of further development of soft, light-driven miniature mechanisms and micro-robots.

scholarly journals Influence of Liquid Crystallinity and Mechanical Deformation on the Molecular Relaxations of an Auxetic Liquid Crystal Elastomer

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7313
Author(s):  
Thomas Raistrick ◽  
Matthew Reynolds ◽  
Helen F. Gleeson ◽  
Johan Mattsson
Keyword(s):  
Liquid Crystal ◽  
Mechanical Response ◽  
Relaxation Times ◽  
Dielectric Relaxation Spectroscopy ◽  
Relaxation Dynamics ◽  
Liquid Crystal Elastomer ◽  
Nematic State ◽  
Out Of Plane ◽  
Liquid Crystal Elastomers ◽  
Polymer Configurations

Liquid Crystal Elastomers (LCEs) combine the anisotropic ordering of liquid crystals with the elastic properties of elastomers, providing unique physical properties, such as stimuli responsiveness and a recently discovered molecular auxetic response. Here, we determine how the molecular relaxation dynamics in an acrylate LCE are affected by its phase using broadband dielectric relaxation spectroscopy, calorimetry and rheology. Our LCE is an excellent model system since it exhibits a molecular auxetic response in its nematic state, and chemically identical nematic or isotropic samples can be prepared by cross-linking. We find that the glass transition temperatures (Tg) and dynamic fragilities are similar in both phases, and the T-dependence of the α relaxation shows a crossover at the same T* for both phases. However, for T>T*, the behavior becomes Arrhenius for the nematic LCE, but only more Arrhenius-like for the isotropic sample. We provide evidence that the latter behavior is related to the existence of pre-transitional nematic fluctuations in the isotropic LCE, which are locked in by polymerization. The role of applied strain on the relaxation dynamics and mechanical response of the LCE is investigated; this is particularly important since the molecular auxetic response is linked to a mechanical Fréedericksz transition that is not fully understood. We demonstrate that the complex Young’s modulus and the α relaxation time remain relatively unchanged for small deformations, whereas for strains for which the auxetic response is achieved, significant increases are observed. We suggest that the observed molecular auxetic response is coupled to the strain-induced out-of-plane rotation of the mesogen units, in turn driven by the increasing constraints on polymer configurations, as reflected in increasing elastic moduli and α relaxation times; this is consistent with our recent results showing that the auxetic response coincides with the emergence of biaxial order.

Effect of stretching angle on the stress plateau behavior of main-chain liquid crystal elastomers

Soft Matter ◽  
2021 ◽  
Vol 17 (11) ◽  
pp. 3128-3136
Author(s):  
Suzuka Okamoto ◽  
Shinichi Sakurai ◽  
Kenji Urayama
Keyword(s):  
Liquid Crystal ◽  
Main Chain ◽  
Stress Plateau ◽  
Liquid Crystal Elastomer ◽  
Ultimate Elongation ◽  
Liquid Crystal Elastomers

Stretching angle for a main-chain liquid crystal elastomer has pronounced effects on the width of the stress plateau as well as the ultimate elongation, while it has no effect on the plateau height.

Bio-inspired thermal-responsive inverse opal films with dual structural colors based on liquid crystal elastomer

2015 ◽  
Vol 3 (17) ◽  
pp. 4424-4430 ◽  
Author(s):  
Huihui Xing ◽  
Jun Li ◽  
Jinbao Guo ◽  
Jie Wei
Keyword(s):  
Liquid Crystal ◽  
Inverse Opal ◽  
Liquid Crystal Elastomer ◽  
Structural Colors ◽  
Thermal Switching ◽  
Liquid Crystal Elastomers

The fabrication of inverse opal micropatterns based on liquid crystal elastomers with dual structural colors and their thermal switching behaviors are described.

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.

Deuteron NMR investigation on orientational order parameter in polymer dispersed liquid crystal elastomers

2020 ◽  
Vol 22 (40) ◽  
pp. 23064-23072
Author(s):  
Andraž Rešetič ◽  
Jerneja Milavec ◽  
Valentina Domenici ◽  
Blaž Zupančič ◽  
Alexej Bubnov ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Order Parameter ◽  
Orientational Order ◽  
Orientational Order Parameter ◽  
Liquid Crystal Elastomer ◽  
H Nmr ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed ◽  
Liquid Crystal Elastomers ◽  
Magnetically Aligned

Orientational order parameter of magnetically aligned liquid crystal elastomer particles suspended in a cured silicone matrix is assessed using 2H-NMR spectroscopy. Obtained results correspond well with the composite's thermomechanical response.

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.

Force Characterization of Hygroscopic Liquid Crystal Elastomers

2010 ◽  
Author(s):  
Michael R. Hays ◽  
Hongbo Wang ◽  
William S. Oates
Keyword(s):  
Liquid Crystal ◽  
Water Vapor ◽  
Water Source ◽  
Vapor Source ◽  
Measuring Device ◽  
Liquid Crystal Elastomer ◽  
Liquid Crystal Elastomers ◽  
Response To Water ◽  
Water Vapor Source

The actuation forces of a hydrophilic liquid crystal elastomer (LCE) in response to water vapor was tested and modeled. These materials exhibit asymmetric swelling as water vapor is absorbed into one side of the elastomer film. This gives rise to deflection away from the water source. Deformation due to water vapor has shown to be on the order of seconds and is reversible which provides unique sensing and actuation characteristics for elastomer films. The constitutive behavior is modeled by using nonlinear continuum mechanics to predict internal changes in density of the liquid crystal elastomer and subsequent deformation by correlating moisture exposure with changes in the elastomer’s density. In order to compare the model and obtain a set material parameters, a micro-Newton measuring device was designed and tested to quantify the forces generated in the liquid crystal elastomer under bending. Forces ranging between 1 to 8 μN were measured as a function of the location of the water vapor source. The results provide important insight into chemical force response and sensing for a number of biomedical and microfluidic applications.

scholarly journals Toward Programmed Complex Stress-Induced Mechanical Deformations of Liquid Crystal Elastomers

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 315 ◽  
Author(s):  
Devesh Mistry ◽  
Helen F. Gleeson
Keyword(s):  
Liquid Crystal ◽  
Complex Stress ◽  
Stress Distributions ◽  
Director Field ◽  
Liquid Crystal Elastomer ◽  
Mechanical Responses ◽  
Mechanical Deformations ◽  
Nonlinear Mechanical ◽  
Liquid Crystal Elastomers ◽  
Spatially Varying

We prepare a liquid crystal elastomer (LCE) with a spatially patterned liquid crystal director field from an all-acrylate LCE. Mechanical deformations of this material lead to a complex and spatially varying deformation with localised body rotations, shears and extensions. Together, these dictate the evolved shape of the deformed film. Using polarising microscopy, we map the local rotation of the liquid crystal director in Eulerian and Lagrangian frames and use these to determine rules for programming complex, stress-induced mechanical shape deformations of LCEs. Moreover, by applying a recently developed empirical model for the mechanical behaviour of our LCE, we predict the non-uniform stress distributions in our material. These results show the promise of empirical approaches to modelling the anisotropic and nonlinear mechanical responses of LCEs which will be important as the community moves toward realising real-world, LCE-based devices.

Polydopamine nanoparticles doped in liquid crystal elastomers for producing dynamic 3D structures

2017 ◽  
Vol 5 (14) ◽  
pp. 6740-6746 ◽  
Author(s):  
Zhen Li ◽  
Yang Yang ◽  
Zhenhua Wang ◽  
Xiaoyong Zhang ◽  
Qiaomei Chen ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Polymer Films ◽  
Smart Materials ◽  
Mechanical Response ◽  
External Stimulus ◽  
3D Structures ◽  
Liquid Crystal Elastomers ◽  
2D Polymer

Achieving 3D structures that can be reversibly formed from dry 2D polymer films is useful for the development of suitable smart materials capable of converting an external stimulus into a mechanical response.

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