Dynamic Liquid Crystal Elastomers for Body Heat‐ and Sunlight‐Driven Self‐Sustaining Motion via Material‐Structure Synergy
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Self‐sustained actuators powered by natural, low‐energy sources based on liquid crystal elastomers (LCEs) are attractive as they offer high safety, abundant energy availability, and practicality in applications. However, achieving stable self‐sustaining motion with low‐energy sources requires high actuation strain rates within a narrow temperature range near ambient conditions—a great challenge as LCEs with low nematic‐to‐isotropic transition temperatures (Tni) generally exhibit reduced actuation strain and strain rates. To address this, we synthesized a carbon nanotube‐doped LCE with a low Tni and reversible Diels‐Alder crosslinks, termed DALCE, and readily (re)fabricated it into specific structures (e.g., twisted‐and‐coiled or bimorph shapes). By leveraging material‐structure synergy, we achieved both low Tni and high actuation strain rates, enabling self‐rolling, self‐breathing and autonomous twisting‐untwisting movements powered by ambient/body temperature or natural sunlight. This low‐energy, self‐sustained actuator design opens new possibilities for LCE‐based biomedical applications and naturally powered automatic devices.Keywords:
Sunlight
Abstract The general rule that addition of a non-mesogenic solute causes a sharp decrease in the nematic-isotropic transition temperature (TN→ I) of a nematic solvent is not obeyed when the solute and solvent can enter into a donor-acceptor interaction. Addition of 4-aminobiphenyl to the nematic liquid crystal 4-cyano-4′-pentylbiphenyl (nematic range ∼ 25–35°) leads to an increase in TN→ I and a decrease in the crystal-nematic transition temperature. The maximum nematic range (21–38°) is achieved at ∼ 7 mole % solute.
Mesogen
Atmospheric temperature range
Biaxial nematic
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Biaxial nematic
Section (typography)
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We propose to measure the ratio κ31 of the bend elastic constant K3 over the splay elastic constant K1 of a nematic phase by using an optical method based on the measurement of the birefringence of homeotropic/planar hybrid samples. This method is compared to the classical measurements using the Freedericksz transition under AC electric field and its advantages and disadvantages are discussed. Both methods are applied to the measurement of K1 and K3 close to the nematic-to-SmA phase transition of the liquid crystal 8CB and the nematic-to-NTB phase transition of the mixture 8CB + 50 wt% CB7CB. The role of flexoelectricity in these measurements is analysed, as well as the role of the pretilt angle and the anchoring energy of the molecules on the plates limiting the samples.
Fréedericksz transition
Homeotropic alignment
Flexoelectricity
Biaxial nematic
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Most liquid crystals consist of molecules shaped like the rod. This chapter focuses on calamitic liquid crystals as they are the most important for applications. Calamitic and thermotropic liquid crystals are important for LCDs. Their nematic phase is the basis for both the most widely used Twisted Nematic cell with active matrix addressing, and for the Super Twist Nematic cell with passive matrix addressing. The liquid crystals used are calamitic and thermotropic in the nematic phase. The operation of this most widely applied LCD is phenomenologically described in order to give an overview over the entire flat panel display system, including the addressing scheme.
Thermotropic crystal
Biaxial nematic
Matrix (chemical analysis)
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Abstract The electric field induced nematic order reconstruction is a way to achieve controlled transitions between uniaxial nematic textures with different topologies, hence allowing intrinsic textural bistability. The order reconstruction connects perpendicular nematic director orientations by exchanging two eigenvalues of the nematic order tensor Q , implying intermediate transient biaxial order. This phenomenon avoids the full nematic melting; in fact the nematic scalar order parameter does not vanish. The Biaxial Order Reconstruction in a calamitic Nematic (BORN) is mainly governed by the biaxial coherence length ξ b . Therefore, by varying ξ b , one can favour or inhibit the transient biaxial order. Recently, it has been demonstrated that ξ b can be controlled by suitable dopants and in this work we study the BORN transition threshold for liquid crystal mixtures made of the commercial nematic liquid crystal E7 and three different metallomesogens with board-like shape. Acknowledgments The authors thank Mauro Ghedini and Daniela Pucci for materials synthesis and helpful discussion and Alfredo Pane for technical assistance.
Biaxial nematic
Bistability
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Abstract An approximate solution is derived for the structure of a twist wall between two regions of opposite 180° twist in a nematic liquid crystal film. The result is used to show that a twist wall is unstable unless the elastic constants of the nematic are such that K22≤ ½(K11 + K33). Thus the observation of such walls in nematic liquid crystals is evidence of this elastic anisotropy. Experimental evidence is given for the validity of the approximate solution obtained.
Biaxial nematic
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Biaxial nematic
Nonane
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Abstract Miscibility phase diagrams of mixtures of side-on side chain liquid crystalline polymers (s-SCLCP) and low molar mass liquid crystals (E48 and E44) have been established by means of polarized optical microscopy and light scattering. E48 and E44 are cyanobiphenyl-based eutectic nematic liquid crystal (LC) mixtures with nematic-isotropic transition temperatures of 93 and 105 C, respectively. The phase diagram of the s-SCLCP/E48 system reveals the coexistence of an isotropic nematic region and a single nematic phase in order of descending temperature. The single nematic phase suggests that the pair is miscible in the nematic region. On the other hand, the s-SCLCP/E44 mixture shows liquid liquid and nematic nematic coexistence phases, suggestive of the immiscibility character of the pair. These nematic phase diagrams of the s-SCLCP/E48 and s-SCLCP/E44 have been analysed in the context of the combined Flory-Huggins (FH) free energy for isotropic mixing and the Maier-Saupe (MS) free energy for nematic ordering of the mesogens. This combined FH/MS theory is capable of predicting the observed nematic phase diagrams consisting of liquid liquid, liquid nematic, nematic nematic, and the pure nematic regions. The change of colour accompanying the appearance and disappearance of the inversion walls may be attributed to the temperature dependence of birefringence.
Biaxial nematic
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Бұл зерттеужұмысындaКaно моделітурaлы жәнеоғaн қaтыстытолықмәліметберілгенжәнеуниверситетстуденттерінебaғыттaлғaн қолдaнбaлы (кейстік)зерттеужүргізілген.АхметЯссaуи университетініңстуденттеріүшін Кaно моделіқолдaнылғaн, олaрдың жоғaры білімберусaпaсынa қоятынмaңыздытaлaптaры, яғнисaпaлық қaжеттіліктері,олaрдың мaңыздылығытурaлы жәнесaпaлық қaжеттіліктерінеқaтыстыөз университетінқaлaй бaғaлaйтындығытурaлы сұрaқтaр қойылғaн. Осы зерттеудіңмaқсaты АхметЯсaуи университетіндетуризмменеджментіжәнеқaржы бaкaлaвриaт бaғдaрлaмaлaрыныңсaпaсынa қaтыстыстуденттердіңқaжеттіліктерінaнықтaу, студенттердіңқaнaғaттaну, қaнaғaттaнбaу дәрежелерінбелгілеу,білімберусaпaсын aнықтaу мен жетілдіружолдaрын тaлдaу болыптaбылaды. Осы мaқсaтқaжетуүшін, ең aлдыменКaно сaуaлнaмaсы түзіліп,116 студенткеқолдaнылдыжәнебілімберугежәнеоның сaпaсынa қaтыстыстуденттердіңтaлaптaры мен қaжеттіліктерітоптықжұмыстaрaрқылыaнықтaлды. Екіншіден,бұл aнықтaлғaн тaлaптaр мен қaжеттіліктерКaно бaғaлaу кестесіменжіктелді.Осылaйшa, сaпa тaлaптaры төрт сaнaтқa бөлінді:болуытиіс, бір өлшемді,тaртымдыжәнебейтaрaп.Соңындa,қaнaғaттaну мен қaнaғaттaнбaудың мәндеріесептелдіжәнестуденттердіңқaнaғaттaну мен қaнaғaттaнбaу деңгейлерінжоғaрылaту мен төмендетудеосытaлaптaр мен қaжеттіліктердіңрөліaйқын aнықтaлды.Түйінсөздер:сaпa, сaпaлық қaжеттіліктер,білімберусaпaсы, Кaно моделі.
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Abstract The crucial role of the smectic A-nematic transitional order for the formation of the smectic A, B and G phases from an electrically deformed nematic phase of the liquid crystal 4-n-hexyloxy-benzylidene-4′-n-butylaniline (6O.4) with a typical smectic A-nematic first order transition and the formation of the smectic A and B phases from an electrically deformed nematic phase of the liquid crystal (4-n-butyloxy-benzylidene-4′-n-octylaniline (40.8) with a smectic A-nematic second order transition has been demonstrated. The nematic phase was deformed by an AC voltage of 2U,th 5U th and 10U th, where U th is the threshold voltage which causes the appearance of the Fréedericksz transition in the homeotropic nematic layer. The smectic textures have been observed on free cooling of the nematic phase or after the use of an oven. The smectic A phase of the liquid crystal 60.4 was observed with the formation of a clear smectic A-nematic phase boundary while the smectic A phase of the liquid crystal 40.8 has been formed from intermediate pretransitional stripes, observed by Cladis and Torza [1]. The homeotropic anchoring of the direction was crucial for the formation of the smectic phases of the liquid crystal 40.8 but not significant for the liquid crystal 60.4.
Homeotropic alignment
Biaxial nematic
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