Nematic main-chain elastomers: Coupling and orientational behavior

Abstract

We summarize investigations on four different nematic main-chain elastomer systems. In the first part, the synthetic approaches towards nematic elastomers with clearing temperatures suitable for mechanical investigations are described. In the second part, the coupling between the liquid crystalline order and the chain conformation is quantified by the Landau-de Gennes coefficient U. Comparing different types of elastomers shows that the coupling depends on the type of mesogens forming the polymer backbone, and on the elastic modulus of the polymer network. In the third part, we compare the orientation behavior of the different systems under strain.

Characterization of Main-Chain Liquid Crystal Elastomers Using X-ray Diffraction Method

“…Mechanical properties of the LCEs can be controlled by selection of liquid crystal phase, density of crosslinkers, their flexible polymer backbones, merger of the backbones, the group of liquid crystals and external stimuli [1,2,4]. The MCLCE materials were synthesized by the reaction of vinyl-or vinoloxy-end mesogens under condition hydrosilylation with crosslinker agent was pentamethylcyclopentasiloxane (C 5 H 20 O 5 Si 2 ) and the mesogen unit was monomer 2-ethyl-1,4-phenylen bis [4 -[4 -(viniloxy) [4,5]. Some studies conducted by previous researcher to show that the MCLCEs have more promising properties compared SCLCEs because of its response to external stimuli such as heat and magnetic field [6].…”

Functional liquid-crystalline polymers and supramolecular liquid crystals

“…211,212 Dense cross-linked nematic and cholesteric materials still exhibit glass transitions (between 40 and 120°C) that are also accompanied by shape deformations. 45,184,213 These properties have been exploited to prepare densely cross-linked nematic or cholesteric polymer networks with intriguing programmable stimuli-responsive properties after their careful alignment. 46,47 The orientation of the LC mixtures is typically induced prior their polymerization by different strategies such as patterned command surfaces or electric fields.…”

“…224 These materials exhibit phase transitions that are often accompanied by shape deformations. 45,217,218,[225][226][227] The basic principle behind the deformation in LC elastomers is depicted in Figure 12. 217 The polymer backbones experience an anisotropic environment in the presence of mesogenic groups.…”

“…When the nematic or smectic LC elastomers are macroscopically aligned, selective shrinkage strain along the director vector is observed during the LC-isotropic phase transitions. 45,47,[219][220][221][222][223][224][225][226][227] Light-induced deformations have been widely explored in crosslinked azobenzene-based LC networks. 220,228 The stimuli response of these materials rely on the light driven cis-trans/trans-cis photoisomerizations of azobenzene groups that act as photochromic molecules Functional liquid-crystalline polymers T Kato et al and as mesogens.…”

“…45 Highly cross-linked side-chain-type polymers [45][46][47] and network polymerizable functional molecules 48,49 have been prepared to develop free-standing and mechanically tough functional polymers.…”