Elastomer bent-core

Bent-core liquid crystalline elastomer Bent-core nematic swollen in a liquid crystal elastomer Black lipid membranes Direct current Electroconvection Electrohydrodynamic Ferroelectric liquid crystal Hybrid-aligned nematic Human embryonic kidney Isotropic... 

Unfortunately swollen LCEs are still not robust enough for long-term operation. However, if the rod-like molecules of a conventional LCE are substituted by BC nematics, a bent-core hquid crystalline elastomer (BCLCE) can be created. BCLCEs might combine excellent flexoelectric properties with rubber elasticity. 

The frequency dependences of the bend fiexoelectric coefficients were also measured for the same BC nematic fluid monomer, BC nematic swollen in a calamitic liquid crystal elastomer (BCN-LCE) and for the bent-core nematic elastomer (BCLCE) as shown in Fig. 3.14. One can see that for each material the fiexoelectric effect was found to be zero below 1 Hz, then the response increases abruptly up to 2 Hz and then decreases slightly. The apparent absence of the response below 1 Hz is probably due to screening by free ions. The slow decrease of the fiexoelectric coefficient at higher / is not yet clear. We assume, however, that it is not a measurement error, because 5CB showed a constant value in this frequency range. 

M. Chambers, R. Verduzco, J.T. Gleeson, S. Sprunt and A. JakU, Calamitic Uquid-crystaUine elastomers swollen in bent-core Uqurd-crystal solvents, Adv. Mater. 21(16), 1622-1626, (2009). doi 10.1002/adma.200802739... 

R. Verduzco, P. Luchette, S.H. Hong, J. Harden, E. DiMasi, P. Palfly-Muhoray, S.M. Kilbey II, S. Sprunt, J.T. Gleeson and A. JakU, Bent-core liquid crystal elastomers, J. Mater. Chem. 20(39), 8488-8495, (2010). doi 10.1039/C0JM01920H... 

Bent-core liquid crystal elastomers have shown to exhibit large values of flexoelectricity as many as three orders of magnitude larger than liquid crystal elastomers containing rod-shaped molecules [44]. These high responses are attributed to a piezoelectric phenomenon. Liquid crystal elastomers combine elasticity and flexibility inherent to rubbers and the optical and electrical properties of liquid crystals, and are promising materials for applications such as electrooptics, flexible electronics, and actuator technologies for biomedical applications. 

A survey of recent studies of biaxial liquid crystals, in the context of the reported biaxial nematic phase in low molecular mass bent-core mesogens, with emphasize on the use of NMR spectroscopy is available. A discussion of orientational order parameters particularly in smectic-C and biaxial nematic phases and their determination by various techniques including NMR has been presented. The relation between molecular dynamics and biaxiality of nematic polymers and elastomers has been studied by H NMR spectroscopy. "" It was observed that the side-on attachment of the mesogens hinder the rotation of the molecules around their long axes and that in nematic polymers and elastomers phase biaxiality... 

Harden, J. Chambers, M. Jakh, A. Verduzco, R. Luchette, P Gleeson, J. T Sprunt, S. Jakli, A. Giant flexoelectricity in bent-core nematic liquid crystal elastomers. Appl. 

Bent-core ferroelectric liquid crystalline elastomer... 

Crosslinking can be used to overcome the aforementioned obstacles, as in the case of the calamitic networks in which the orientation and polarity are preserved. First experiments were performed by swelling a calamitic LCE with a low-molar-mass BCLC [182, 183]. Up to 35 mol% of this material could be incorporated into the network. The resulting gel had a flexoelectric cmistant e-i of 20 nC/m. This is one-third of the value of the low-molar-mass BCLC, which corresponds to the volume fraction of the BCLC. Only recently has a pure bent-core elastomer (BCFLCE) been made [139, 169]. Following the synthetic route of Finkelmann, an oriented, transparent nematic elastomer sample could be obtained. As a polysiloxane backbone was used, the Tg was close to room temperature. The flexoelectric constant of 40 nC/m is somewhat smaller than for the pure bend-core monomer, but larger than the value obtained for the swollen elastomer. 

Verduzco R, Luchette P, Hong SH, Harden J, DiMasi E, Palffy-Muhoray P, Kilbey SM, Sprunt S, Gleeson JT, Jakli A (2010) Bent-core liquid crystal elastomers. J Mater Chem 20(39) 8488-8495. doi 10.1039/c0jm01920h... 

Chambers M, Verduzco R, Gleeson JT, Sprunt S, Jakli A (2009) Flexoelectricity of a calamitic liquid crystal elastomer swollen with a bent-core liquid crystal. J Mater Chem 19(42) 7909-7913. doi 10.1039/b911652d... 

Thisayukta J, Nakayama Y, Kawauchi S, Takezoe H, Watanabe J (2000) Distinct formation of a chiral smectic phase in achiral banana-shaped molecules with a central core based on a 2,7-dihydroxynaphthalene unit. J Am Chem Soc 122 7441-7448 Tschierske C, Dantlgraber G (2003) From antiferroelectricity to ferroelectricity in smectic mesophases formed by bent-core molecules. Pramana J Phys 61 455-481 Ungar G, Percec V, Zuber M (1992) Liquid crystalline polyethers based on conformational isomerism. 20. Nematic-nematic transition in polyethers and copolyethers based on l-(4-hydroxyphenyl)2-(2-R-4-hydroxyphenyl)ethane with R=lluoro, chloro and methyl and flexible spacers containing an odd number of methylene units. Macromolecules 25 75-80 Urayama K (2007) Issues in liquid crystal elastomers and gels. Macromolecules 40 2277-2288 Vorlander D (1908) About transparently clear, crystalline liquids. Rep Ger Chem Soc 41 2033-2052... 

---