scholarly journals Numerical Methods in Studies of Liquid Crystal Elastomers

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1650
Author(s):  
Madjid Soltani ◽  
Kaamran Raahemifar ◽  
Arman Nokhosteen ◽  
Farshad Moradi Kashkooli ◽  
Elham L. Zoudani
Keyword(s):  
Liquid Crystal ◽  
Numerical Models ◽  
Future Research ◽  
Artificial Muscles ◽  
Suitable Candidate ◽  
Numerical Studies ◽  
Wide Range ◽  
Electric And Magnetic Fields ◽  
Liquid Crystal Elastomers ◽  
External Stimuli

Liquid crystal elastomers (LCEs) are a type of material with specific features of polymers and of liquid crystals. They exhibit interesting behaviors, i.e., they are able to change their physical properties when met with external stimuli, including heat, light, electric, and magnetic fields. This behavior makes LCEs a suitable candidate for a variety of applications, including, but not limited to, artificial muscles, optical devices, microscopy and imaging systems, biosensor devices, and optimization of solar energy collectors. Due to the wide range of applicability, numerical models are needed not only to further our understanding of the underlining mechanics governing LCE behavior, but also to enable the predictive modeling of their behavior under different circumstances for different applications. Given that several mainstream methods are used for LCE modeling, viz. finite element method, Monte Carlo and molecular dynamics, and the growing interest and reliance on computer modeling for predicting the opto-mechanical behavior of complex structures in real world applications, there is a need to gain a better understanding regarding their strengths and weaknesses so that the best method can be utilized for the specific application at hand. Therefore, this investigation aims to not only to present a multitude of examples on numerical studies conducted on LCEs, but also attempts at offering a concise categorization of different methods based on the desired application to act as a guide for current and future research in this field.

scholarly journals Shape-Memory Polymeric Artificial Muscles: Mechanisms, Applications and Challenges

Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4246 ◽  
Author(s):  
Yujie Chen ◽  
Chi Chen ◽  
Hafeez Ur Rehman ◽  
Xu Zheng ◽  
Hua Li ◽  
...  
Keyword(s):  
Shape Memory ◽  
Smart Materials ◽  
Recent Progress ◽  
Shape Memory Polymer ◽  
Shape Memory Polymers ◽  
Artificial Muscles ◽  
Linkage Design ◽  
Wide Range ◽  
Liquid Crystal Elastomers ◽  
Made In

Shape-memory materials are smart materials that can remember an original shape and return to their unique state from a deformed secondary shape in the presence of an appropriate stimulus. This property allows these materials to be used as shape-memory artificial muscles, which form a subclass of artificial muscles. The shape-memory artificial muscles are fabricated from shape-memory polymers (SMPs) by twist insertion, shape fixation via Tm or Tg, or by liquid crystal elastomers (LCEs). The prepared SMP artificial muscles can be used in a wide range of applications, from biomimetic and soft robotics to actuators, because they can be operated without sophisticated linkage design and can achieve complex final shapes. Recently, significant achievements have been made in fabrication, modelling, and manipulation of SMP-based artificial muscles. This paper presents a review of the recent progress in shape-memory polymer-based artificial muscles. Here we focus on the mechanisms of SMPs, applications of SMPs as artificial muscles, and the challenges they face concerning actuation. While shape-memory behavior has been demonstrated in several stimulated environments, our focus is on thermal-, photo-, and electrical-actuated SMP artificial muscles.

scholarly journals Digital light processing of liquid crystal elastomers for self-sensing artificial muscles

2021 ◽  
Vol 7 (30) ◽  
pp. eabg3677
Author(s):  
Shuo Li ◽  
Hedan Bai ◽  
Zheng Liu ◽  
Xinyue Zhang ◽  
Chuqi Huang ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Optical Transition ◽  
Orientational Order ◽  
Weight Ratio ◽  
Great Promise ◽  
Artificial Muscles ◽  
Specific Work ◽  
Digital Light Processing ◽  
Stimuli Responsive Polymers ◽  
Liquid Crystal Elastomers

Artificial muscles based on stimuli-responsive polymers usually exhibit mechanical compliance, versatility, and high power-to-weight ratio, showing great promise to potentially replace conventional rigid motors for next-generation soft robots, wearable electronics, and biomedical devices. In particular, thermomechanical liquid crystal elastomers (LCEs) constitute artificial muscle-like actuators that can be remotely triggered for large stroke, fast response, and highly repeatable actuations. Here, we introduce a digital light processing (DLP)–based additive manufacturing approach that automatically shear aligns mesogenic oligomers, layer-by-layer, to achieve high orientational order in the photocrosslinked structures; this ordering yields high specific work capacity (63 J kg−1) and energy density (0.18 MJ m−3). We demonstrate actuators composed of these DLP printed LCEs’ applications in soft robotics, such as reversible grasping, untethered crawling, and weightlifting. Furthermore, we present an LCE self-sensing system that exploits thermally induced optical transition as an intrinsic option toward feedback control.

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.

Experimental Studies of Thermo-Induced Mechanical Effects in the Main-Chain Liquid Crystal Elastomers

2014 ◽  
Vol 896 ◽  
pp. 322-326 ◽  
Author(s):  
Supardi ◽  
Harsojo ◽  
Yusril Yusuf
Keyword(s):  
Liquid Crystal ◽  
Critical Temperature ◽  
Main Chain ◽  
Experimental Studies ◽  
Artificial Muscles ◽  
Direction Parallel ◽  
Mechanical Effects ◽  
Liquid Crystal Elastomers ◽  
Heating Up ◽  
Contraction And Expansion

Liquid crystal elastomers (LCEs), either side-chain LCEs (SCLCEs) or main-chain LCEs (MCLCEs), possess a combination of LC and elastic properties, and are expected to be used as artificial muscles. We experimentally investigated the thermo-induced mechanical effects showed by MCLCEs with four different crosslinker concentrations, i.e., 8%, 12%, 14% and 16%. The samples were heated up to the critical temperature and the images were recorded. The samples made the contraction in direction parallel to the director and the expansion in direction perpendicular to the director. Drastic changes occured when approaching the critical temperature, the greater the crosslinkers concentration the bigger the maximum contraction and expansion. The shape anisotropy expression showed that heating up to the critical temperature caused the system no longer in anisotropic state.

Thermo-, photo-, and mechano-responsive liquid crystal networks enable tunable photonic crystals

Soft Matter ◽  
2017 ◽  
Vol 13 (41) ◽  
pp. 7486-7491 ◽  
Author(s):  
N. Akamatsu ◽  
K. Hisano ◽  
R. Tatsumi ◽  
M. Aizawa ◽  
C. J. Barrett ◽  
...  
Keyword(s):  
Optical Properties ◽  
Liquid Crystal ◽  
Photonic Crystals ◽  
Liquid Crystal Elastomers ◽  
External Stimuli

Tunable photonic crystals exhibiting optical properties that respond reversibly to external stimuli have been developed using liquid crystal networks (LCNs) and liquid crystal elastomers (LCEs).

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.

scholarly journals Instabilities in liquid crystal elastomers

MRS Bulletin ◽  
2021 ◽  
Author(s):  
L. Angela Mihai ◽  
Alain Goriely
Keyword(s):  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Void Nucleation ◽  
Stochastic Methods ◽  
Model Parameters ◽  
Homogeneous State ◽  
Mechanical Effects ◽  
Liquid Crystal Elastomers ◽  
External Stimuli ◽  
Constitutive Parameters

AbstractStability is an important and fruitful avenue of research for liquid crystal elastomers. At constant temperature, upon stretching, the homogeneous state of a nematic body becomes unstable, and alternating shear stripes develop at very low stress. Moreover, these materials can experience classical mechanical effects, such as necking, void nucleation and cavitation, and inflation instability, which are inherited from their polymeric network. We investigate the following two problems: First, how do instabilities in nematic bodies change from those found in purely elastic solids? Second, how are these phenomena modified if the material constants fluctuate? To answer these questions, we present a systematic study of instabilities occurring in nematic liquid crystal elastomers, and examine the contribution of the nematic component and of fluctuating model parameters that follow probability laws. This combined analysis may lead to more realistic estimations of subsequent mechanical damage in nematic solid materials. Because of their complex material responses in the presence of external stimuli, liquid crystal elastomers have many potential applications in science, manufacturing, and medical research. The modeling of these materials requires a multiphysics approach, linking traditional continuum mechanics with liquid crystal theory, and has led to the discovery of intriguing mechanical effects. An important problem for both applications and our fundamental understanding of nematic elastomers is their instability under large strains, as this can be harnessed for actuation, sensing, or patterning. The goal is then to identify parameter values at which a bifurcation emerges, and how these values change with external stimuli, such as temperature or loads. However, constitutive parameters of real manufactured materials have an inherent variation that should also be taken into account, thus the need to quantify uncertainties in physical responses, which can be done by combining the classical field theories with stochastic methods that enable the propagation of uncertainties from input data to output quantities of interest. The present study demonstrates how to characterize instabilities found in nematic liquid crystal elastomers with probabilistic material parameters at the macroscopic scale, and paves the way for a systematic theoretical and experimental study of these fascinating materials.

Robust and Reprocessable Artificial Muscles Based on Liquid Crystal Elastomers with Dynamic Thiourea Bonds

2021 ◽  
pp. 2110360
Author(s):  
Jin‐Hyeong Lee ◽  
Jaehee Bae ◽  
Jae Hyuk Hwang ◽  
Moon‐Young Choi ◽  
Yong Seok Kim ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Artificial Muscles ◽  
Liquid Crystal Elastomers

scholarly journals Considerations for Numerical Modeling of the Pulmonary Circulation—A Review With a Focus on Pulmonary Hypertension

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
V. O. Kheyfets ◽  
W. O'Dell ◽  
T. Smith ◽  
J. J. Reilly ◽  
E. A. Finol
Keyword(s):  
Blood Flow ◽  
Pulmonary Hypertension ◽  
Pulmonary Blood Flow ◽  
Numerical Models ◽  
Academic Research ◽  
Basic Research ◽  
Wall Stress ◽  
Pulmonary Vasculature ◽  
Future Research ◽  
Wide Range

Both in academic research and in clinical settings, virtual simulation of the cardiovascular system can be used to rapidly assess complex multivariable interactions between blood vessels, blood flow, and the heart. Moreover, metrics that can only be predicted with computational simulations (e.g., mechanical wall stress, oscillatory shear index, etc.) can be used to assess disease progression, for presurgical planning, and for interventional outcomes. Because the pulmonary vasculature is susceptible to a wide range of pathologies that directly impact and are affected by the hemodynamics (e.g., pulmonary hypertension), the ability to develop numerical models of pulmonary blood flow can be invaluable to the clinical scientist. Pulmonary hypertension is a devastating disease that can directly benefit from computational hemodynamics when used for diagnosis and basic research. In the present work, we provide a clinical overview of pulmonary hypertension with a focus on the hemodynamics, current treatments, and their limitations. Even with a rich history in computational modeling of the human circulation, hemodynamics in the pulmonary vasculature remains largely unexplored. Thus, we review the tasks involved in developing a computational model of pulmonary blood flow, namely vasculature reconstruction, meshing, and boundary conditions. We also address how inconsistencies between models can result in drastically different flow solutions and suggest avenues for future research opportunities. In its current state, the interpretation of this modeling technology can be subjective in a research environment and impractical for clinical practice. Therefore, considerations must be taken into account to make modeling reliable and reproducible in a laboratory setting and amenable to the vascular clinic. Finally, we discuss relevant existing models and how they have been used to gain insight into cardiopulmonary physiology and pathology.

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