Swelling dynamics of liquid crystal elastomers swollen with low molecular weight liquid crystals

Abstract

We experimentally investigated the swelling behavior of thin films (approximately 150 microm) 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 empty set 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 axially n empty set than radially n empty set. Second, only the LSCE dimensions radially n empty set expanded, while that axially n empty set 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.

Main Chain Liquid-Crystalline Elastomers: Swelling Dynamics and Electromechanical Effects

“…No dimension changes parallel to the director n could be observed during the swelling in 8A2 [6]. We believe this is because the crosslinkers in that LCE system order essentially parallel to the tethered mesogenic side chains due to their chemical constitution (the mesogenic units are oriented parallel to the stretching direction, fix a length scale in kn n), resulting in networks with 'equasi-smectic' ordering, i.e., larger frozen-in orientational order (FOO) [6]. In contrast, V3LSCE swells in kn n because its cross-linker (trifunctional type) has isotropic-like property which reducing the degree of FOO [7], comparing to the bifunctional cross-linker which has anisotropic property.…”

“…They were swollen with a low molecular weight liquid crystals, 4-n-pentyl-4-cyanobiphenyl (5CB), an anisotropic solvent. In particular, we found that the swelling properties and temperature behavior (thermomechanical property) of volume changes were also anisotropic [5][6][7]. The magnitude of the swelling anisotropy depended on the cross-linking concentration.…”

“…In previous studies [6,7] we used the side-chain LCE (SCLCE) with different cross-linking agents, i.e., bifunctionally (8A2) and trifunctionally (V3) cross-linked LCEs; monodomain (LSCE, liquid single crystal elastomers) and polydomain LCEs. They were swollen with a low molecular weight liquid crystals, 4-n-pentyl-4-cyanobiphenyl (5CB), an anisotropic solvent.…”

“…[1][2][3][4]. On the other hand, a liquid-crystal elastomer (LCE), an anisotropic gel, has been recently synthesized, for which swelling properties and temperature behavior in an anisotropic solvent such as low molecular weight liquid crystals (LMWLC) are different from the well-known isotropic case [5][6][7][8][9][10].…”

Loading effect on swelling of nematic elastomers

“…If the solvent has nematicity, the nematic order of the surrounding solvent also influences the swelling. [9][10][11][12] These swelling behaviors are governed by the orientational orders of the constituent LCs, and they are described by a mean field theory. [13][14][15][16] The characteristic swelling dynamics was also revealed by the temperature-jump experiments.…”