Electrooptical Effects of Swollen Polydomain Liquid Crystal Elastomers (original) (raw)
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Low-voltage-driven electromechanical effects of swollen liquid-crystal elastomers
Physical Review E, 2005
We experimentally investigate, in detail, electromechanical effects in liquid-crystal elastomers ͑LCEs͒ previously swollen with low-molecular-weight liquid crystals ͑LMWLCs͒. Both polydomain ͑POLY͒ and monodomain ͑MONO͒ LCEs were studied. We used a well known LMWLC, 4-n-pentyl-4-cyanobiphenyl ͑5CB͒ as a solvent. After swelling POLY and MONO LCEs ͑LSCE͒ with 5CB, shape changes were measured by recording the displacement of the edge of the swollen LCE at different voltages, V, and temperature. With 100 m distance between electrodes, measurable shape changes ͑ϳ1-20 m͒ are observed with small voltages ͑V ϳ 0.5-10 V͒. In particular, we note that, compared to unswollen L͑S͒CEs, a dramatic ϳ200 times decrease of the threshold field was found for electromechanical effects in swollen L͑S͒CEs. While swollen MONO LCEs showed electromechanical effects in the planar geometry, homeotropic MONO swollen with homeotropically oriented 5CB did not. This is easy to understand because, in the homeotropic case, the liquid-crystal preferred axis is already aligned with the field so the field has no reorienting effect. The inverse of the response time when the field was switched on in both POLY and MONO was proportional to E 2 , which is the same field dependence as the response time of LMWLCs. When the field was switched off, the relaxation time showed a field dependence different from that of LMWLCs that we attribute to relaxation of the LCE network.
Multifunctional liquid crystal elastomers: Large electromechanical and electro-optical effects
Applied Physics Letters, 2008
A multifunctional main chain liquid crystal elastomer ͑MCLCE͒ with large mechanical and optical effects in applied electric fields is investigated, when MCLCE is swollen in a low molecular weight liquid crystal, 4-n-pentyl-4-cyanobiphenyl, a nematic solvent. The size change by the field effects is linearly proportional to the transmittancy change. This suggests the possibility of broad application as a field-induced-optical actuator device.
Journal of the Physical Society of Japan, 2005
We report electromechanical effects in a swollen polydomain liquid crystalline elastomer (POLY-LCE). Owing to the director reorientation, we could directly observe its deformation in the unconstrained elastomer gel state. Using optical image analysis, the deformation amplitude, threshold voltage, and temporal characteristics of the POLY-LCE were quantitatively measured with varying voltage and temperature. From the experimental results we discuss the deformation mechanism and property of the POLY-LCE.
Swelling dynamics of liquid crystal elastomers swollen with low molecular weight liquid crystals
Physical Review E - PHYS REV E, 2004
We experimentally investigated the swelling behavior of thin films (˜150 μm) of liquid crystalline elastomers (LCEs) by low molecular weight liquid crystals (LMWLCs). The two LMWLCs used are the well-known nematic liquid crystals, 4-n-pentyl-4-cyanobiphenyl, and 4-methoxy-benzilidene-4-butyl-aniline. Both polydomain (POLY) and monodomain (MONO) LCE swelling are studied. In MONO LCEs (LSCEs), the director n^ is uniformly oriented throughout the film. POLY films are made of many domains with different orientations. Its swelling behavior was similar to isotropic gels. In contrast, LSCEs revealed interesting results not anticipated by any theory. First, the LMWLC enters the LSCE by front propagation about three-times faster ‖n^ than ⊥n^. Second, only the LSCE dimensions ⊥n^ expanded, while that ‖n^ did not change at all. Third, when the LMWLC director and the LSCE director are aligned (MONO2 samples), swelling takes place about twice as fast as when they are not aligned. Volume change dynamics of swollen L(S)CEs investigated as a function of temperature revealed several phase transitions by optical and calorimetry techniques.
Physical Review E
We investigate light-induced patterning of a monodomain side-chain liquid crystal elastomer (SC-LCE) doped with light-sensitive azobenzene moiety in the temperature region close to the nematic-paranematic phase transition. We show that a strongly nonlinear relationship between the concentration of the cis isomers of the azomesogens and the refractive index modification of the material, which is characteristic for the phase transition region, results in nonmonotonous time dependence of the diffraction efficiency of a probe beam. From this effect we determine the sensitivity of the nematic transition temperature on the molar fraction of the cis isomers. The relation between the cis isomer molar fraction and nematic order also provides a possibility for recording hidden holograms, which can be made visible by cooling the sample from the paranematic to the nematic phase.
Mechanisms leading to fast relaxation of liquid crystal cells aligned with conductive polymers
Journal of Applied Physics, 2010
Using nematic liquid crystal cells aligned by conductive polymers, like polyaniline or doped polypyrrole, a very fast electro-optic response is observed. We show that when a switch that interrupts the voltage across the cell is placed between the cell and the ground, the largest voltage drop is on the switch in its open position. The voltage distribution among the nematic cell and the switch is evaluated. The role played in this very fast electro-optic response of the ionic charges built on the interfaces together with the redox processes among the free charges in the polymer-liquid crystal interface is also described. For an asymmetric cell ͑only one side covered with a conductive polymer͒ a rectifying effect appears. In this case a circuital model is used to mimic the steplike behavior of the transmitted light during the relaxation of the system.