Low-voltage-driven electromechanical effects of swollen liquid-crystal elastomers

Abstract

We experimentally investigate, in detail, electromechanical effects in liquid-crystal elastomers (LCEs) previously swollen with low-molecular-weight liquid crystals (LMWLCs). Both polydomain (POLY) and monodomain (MONO) LCEs were studied. We used a well known LMWLC, 4-n-pentyl-4-cyanobiphenyl (5CB) as a solvent. After swelling POLY and MONO LCEs (LSCE) 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 microm distance between electrodes, measurable shape changes (approximately 1-20 microm) are observed with small voltages (V approximately 0.5-10 V). In particular, we note that, compared to unswollen L(S)CEs, a dramatic approximately 200 times decrease of the threshold field was found for electromechanical effects in swollen L(S)CEs. 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 E2, 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.

Hydrodynamic description of elastic or viscoelastic composite materials: Relative strains as macroscopic variables

“…These may be selectively reoriented using externally applied fields. For instance, in liquid crystal elastomers [6,35,63], relative rotations were generated via external electric fields acting on the liquid crystalline component in a swollen state [63][64][65][66]. Likewise, anisotropic magnetic inclusions could be selectively reoriented by magnetic fields [67,68].…”

Instabilities in nematic elastomers in external electric and magnetic fields

“…However, the corresponding values should be achievable in experiments nowadays. Furthermore, swelling nematic SCLSCEs with common LMWLCs as was done for example in references [10,12] drastically reduces the necessary field amplitudes. Our results should describe the effects observed in these materials in the same way, as long as electric currents do not lead to dominating different effects and as long as the different mesogens of the SCLSCE and the LMWLC show the same behavior of reorientation.…”

“…It is worthwhile to investigate the behavior of SCLSCEs when exposed to an external electric or magnetic field, also in view of their potential applications which include, e.g., artificial muscles [8][9][10]. The geometries that we want to study in the following correspond to those suitable to observe the classical Frederiks transition in common low molecular weight liquid crystals (LMWLCs).…”

Functional liquid-crystalline polymers and supramolecular liquid crystals

“…[246][247][248][249] Remarkably, LC chemical gels also show shape variations in response to temperature and external fields. [250][251][252][253][254][255] Thermal actuation in LC chemical gels is often accompanied by volume variations. 251,252 Urayama and co-workers extensively studied the polymerized mixtures of mesogenic acrylates and diacrylates in LC solvents.…”

“…253 Actuation in LC physical gels have been induced not only by temperature variations, but also by application of electric fields. 254,255 LC physical gels are formed by micro-phase separation of liquid crystal solvents and supramolecular gelators forming fibrous aggregates. 241,242 Liquid crystals exhibiting nematic, cholesteric, smectic and columnar phases have been used to prepare LC gels.…”