Metallo-, Thermo-, and Photoresponsive Shape Memory and Actuating Liquid Crystalline Elastomers

Abstract

A liquid crystalline elastomer incorporating a mesogenic derivative of the 2,6-bisbenzimidazolylpyridine (Bip) ligand has been prepared, and its shape memory and actuating properties have been studied. The reversible liquid crystal to isotropic transition is utilized as the switching mechanism for these stimuli-responsive materials. As such, this material exhibits soft shape memory; that is, flexibility is retained in both the permanent and temporary shapes. In addition to the thermal shape memory/actuating properties exhibited by most liquid crystalline elastomers, the incorporation of the metal ion-binding Bip mesogen into the backbone of the network imparts both (i) photoresponsive properties, via a photothermal conversion process, and (ii) metal-ion-triggered shape recovery/actuation to the material. For the latter process, it is proposed that the metal-binding event induces liquid crystalline to isotropic transition in this material at room temperature, resulting in actuation/recovery of the permanent shape.

Physio- and chemo-dual crosslinking toward thermoand photo-response of azobenzene-containing liquid crystalline polyester

“…For PBHPS-3%PTA, the peaks in the small angle range were negligible, because the relative high content of PTA influenced the chain folding or arrangement, thus destroyed the orderly structure between the layers. For PBHPS, there was a peak at the angle of 28.1°(0.32 nm) which indicated the π-π interactions between the phenyl rings exiting in the polymer chains as reported previously [23,26]. When 1% of PTA was incorporated, peaks in this area still existed, impling the π-π interactions remained in PBHPS-1%PTA.…”

“…4 shows the liquid crystalline textures of PBHPS and PBHPS-x%PTA on the first cooling process, which were observed and captured at 40°C by using a POM. All the slightly crosslinking samples showed the typical focal conic textures as PBHPS did [26], which implied the small quantity of PTA incorporated into the PBHPS chains did not change the molecular mobility and regular packing, as illustrated in DSC test. WAXD analysis was also used to determine the microstructure of the polyesters.…”

“…[24][25][26][27][28][29], where different secondary bonds might be another answer, including hydrogen bond, π-π interaction, coordination linkage, and so on. For example, Ikeda et al [30] prepared azo based liquid crystalline films using hydrogen bond as crosslinking points, obtaining the reversible bending/unbending properties under UV/visible light as well.…”

Preparation of liquid crystalline polymer networks containing a cinnamyl group in the main chain with tunable thermal actuation behavior

“…As early as 1975, P. G. de Gennes predicted that liquid crystal elastomers (LCEs) could realize the functions of human muscles. LCEs are soft materials that can produce a large mechanical actuation and reversible shape change when subjected to various external stimuli, and they have potential applications in artificial muscles, soft robots, and dynamic functional architectures . An LCE can be obtained by moderately crosslinking a liquid crystalline copolyester (LCP) and exhibits elasticity in the isotropic or liquid crystal state while having the dual characteristics of an elastomer and a liquid crystal.…”

Liquid crystal elastomer actuators: Synthesis, alignment, and applications

“…LCE synthesis via the use of LC polymer as a starting material has been widely used for the synthesis of a variety of LCEs . The synthesis of LCE incorporated with metal ion‐binding Bip mesogen will be another unique example that used this synthetic route . However, the higher viscosity of the starting material largely limits alignment techniques to mechanical alignment to generate monodomain LCEs.…”