Elastocaloric effect in liquid crystal elastomers from molecular simulations

Skačej, Gregor

doi:10.1080/02678292.2018.1492035

Cited by 15 publications

(9 citation statements)

References 21 publications

(34 reference statements)

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“…Our molecular simulations largely follow the methodology presented in Ref. [34]. In the simulation, mesogenic units are represented by uniaxial ellipsoidal particles interacting via the soft-core Gay-Berne (GB) potential [35,36].…”

Section: Sample Preparation Procedures and Experimentalmentioning

confidence: 99%

“…The less densely crosslinked sample presents a slightly lower nematicisotropic transition temperature and a steeper temperature dependence of near the nematicisotropic phase transition in comparison with its more densely crosslinked counterpart. Now, the elastocaloric response is dominated by the absolute value of the derivative ( ) [31][32][33][34], i.e., higher slopes result in a more pronounced response. In addition, a steeper slope also indicates that the transition moves toward the first order regime below the critical point in agreement with early experiments [31,32].…”

Section: A Monte Carlo Simulations and The Thermomechanical Responsementioning

confidence: 99%

“…It was shown recently that in side-chain LCEs an elastocaloric effect of ΔT eCE = 0.4 K can be observed already at a moderate stress field of  = 0.13 MPa, thus demonstrating very large elastocaloric responsivity ΔT eCE / = 4 K/MPa [26]. These initial experimental investigations of caloric effects in LCEs [26] has been followed by a recent molecular computer simulation study [34], suggesting that the elastocaloric temperature change and responsivity observed so far in real experiments could be substantially improved.…”

Section: Introductionmentioning

confidence: 97%

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Tunability of the elastocaloric response in main-chain liquid crystalline elastomers

et al. 2020

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Materials exhibiting a large caloric effect could lead to the development of new generation of heat-management technologies that will have better energy efficiency and be potentially more environmentally friendly. The focus of caloric materials investigations has shifted recently from solid-state materials toward soft materials, such as liquid crystals and liquid crystalline elastomers. It has been shown recently that a large electrocaloric effect exceeding 7 K can be observed in smectic liquid crystals. Here, we report on a significant elastocaloric response observed by direct elastocaloric measurements in main-chain liquid crystal elastomers. It is demonstrated that the character of the nematic to paranematic/isotropic transition can be tuned from the supercritical regime towards the first-order regime, by decreasing the density of crosslinkers. In the latter case, the latent heat additionally enhances the elastocaloric response. Our results indicate that a significant elastocaloric response is present in main-chain liquid crystalline elastomers, driven by stress fields much smaller than in solid elastocaloric materials. Therefore, elastocaloric soft materials can potentially play a significant role as active cooling/heating elements in the development of new heat-management devices.

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Section: Sample Preparation Procedures and Experimentalmentioning

confidence: 99%

Section: A Monte Carlo Simulations and The Thermomechanical Responsementioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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Tunability of the elastocaloric response in main-chain liquid crystalline elastomers

et al. 2020

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“…Experimental efforts have so far demonstrated elastocaloric temperature changes of only ∆T ∼ 1 K. 14,22 Lavrič et al observed ∆T = 1 K at a strain of ε = 90% and detailed that this ∆T was observed across a range of crosslink density. 22 Skačej has reported molecular simulations that suggest the elastocaloric effect in mainchain LCEs could yield a ∆T > 10 K. 23 However, the simulations underestimate the specific heat of liquid crystal-containing systems, which likely leads to an overestimate of the elastocaloric temperature change. LC systems also have been explored as electrocaloric materials, notably harnessing a smectic-to-isotropic transition to achieve a ∆T + of up to 5.2 to 6.5 K. 14,24 Our group has recently quantified the transition from disorder (order parameter Q ≈ 0) to appreciable order (Q ≈ 0.4, i.e., the nematic phase) in a liquid crystal-containing elastomeric network upon application of uniaxial strain.…”

Section: Introductionmentioning

confidence: 99%

Elastocaloric effect in amorphous polymer networks undergoing mechanotropic phase transitions

Koch,

Herman,

White

2021

Preprint

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Deformations of amorphous polymer networks prepared with significant concentrations of liquid crystalline mesogens have been recently reported to undergo mechanotropic phase transitions. Here, we report that these mechanotropic phase transitions are accompanied by an elastocaloric response (∆T = 2.9 K). Applied uniaxial strain to the elastomeric polymer network transitions the organization of the material from a disordered, amorphous state (order parameter Q = 0) to the nematic phase (Q = 0.47). Both the magnitude of the elastocaloric temperature change and mechanically induced order parameter are dependent on the concentration of liquid crystal mesogens in the material. While the observed temperature changes in these materials are smaller than those observed in shape memory alloys, the responsivity, defined as the temperature change divided by the input stress, is larger by an order of magnitude.

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“…This process is macroscopically manifested as the size shrinkage of LCEs in the orientation direction. [40,41] Therefore, the orientation degree of LCEs affects the maximum deformation actuated by the external stimuli to a large extent, whereas the orientation direction of LCEs determines their macroscopic deformation direction. The programmability of the mesogen orientation lays a foundation for achieving versatile deformation actuations of LCEs.…”

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confidence: 99%

Varied Alignment Methods and Versatile Actuations for Liquid Crystal Elastomers: A Review

Zhao

Zhang

2021

Advanced Intelligent Systems

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Liquid crystal elastomers (LCEs) are a class of polymer materials that can produce reversible strain responses under heat, [1,2] light, [3][4][5][6] electric field [7] (or electric induction heat), [8,9] magnetic field (or magnetic induction heat), [10,11] moisture, [12] or solvent, [13] etc. They have attracted intense attention due to their enormous potential applications in soft robots, [1,9,[14][15][16][17][18] soft actuators, [4,8,14,[19][20][21][22][23] sensors, [22,[24][25][26] artificial muscles, [27][28][29] biomedicine, [30,31] flexible electronics, [32,33] light energy collection, [34] etc.LCEs are composed of rigid mesogens and flexible polymer networks, with the result that the anisotropy of liquid crystal and the rubber elasticity of polymer network can be both shown in LCEs. [35][36][37] Induced by mechanical stress, external field, or surface effect, the long axes of the mesogens can be aligned into specific directions (expressed by the director n), and this process is called alignment. Liquid crystal polymers after alignment are chemically [38] or physically [39] crosslinked to form anisotropic monodomain (including nematic, smectic, or cholesteric) LCEs. On the contrary, LCEs are in a polydomain state with isotropy when the directors of liquid crystal domains are arranged disorderly. Triggered by the external physical or chemical stimuli, the response and deformation originated from the phase transition from a liquid crystalline phase to an isotropic phase is significantly enhanced in the monodomain LCEs. This process is macroscopically manifested as the size shrinkage of LCEs in the orientation direction. [40,41] Therefore, the orientation degree of LCEs affects the maximum deformation actuated by the external stimuli to a large extent, whereas the orientation direction of LCEs determines their macroscopic deformation direction. The programmability of the mesogen orientation lays a foundation for achieving versatile deformation actuations of LCEs. [42] Aligning the mesogen orientation and achieving versatile actuations of LCEs are always the central research objects in the field of LCEs, and have developed rapidly in recent years. However, few reviews are addressing these two important issues simultaneously.Herein, in Section 1, we briefly elucidate the relationships between the microscopic orientation structure of LCEs, external stimuli, and macroscopic deformation characteristics of LCEs. In Section 2, we introduce three types of LCE alignment methods and their basic principles, and focus on comparing their programmability toward the mesogen orientation. In Section 3, we summarize two types of actuations for LCEs on the basis of the latest development, and focus on comparing their deformation controllability. In Section 4, we propose an outlook for the future key technologies to develop versatile, precise, and fastresponsive deformation actuations for LCEs. This review aims to help people to design and prepare LCEs with programmable orientation structure and excellent actuation characteristic...

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Elastocaloric effect in liquid crystal elastomers from molecular simulations

Cited by 15 publications

References 21 publications

Tunability of the elastocaloric response in main-chain liquid crystalline elastomers

Tunability of the elastocaloric response in main-chain liquid crystalline elastomers

Elastocaloric effect in amorphous polymer networks undergoing mechanotropic phase transitions

Varied Alignment Methods and Versatile Actuations for Liquid Crystal Elastomers: A Review

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