Photomechanical Motion of Liquid-Crystalline Fibers Bending Away from a Light Source

Abstract

A series of photomechanical fibers was fabricated with a thermal drawing method by using liquid-crystalline random copolymers containing azobenzene and biphenyl groups in side chain. After being post-cross-linked under mild conditions, these fibers showed photoinduced bending motion away from the light source even though homogeneous alignment of mesogens was observed along the drawing direction. This abnormal photoinduced deformation of the obtained fibers is far different from previously reported light-directed motions about liquid-crystalline fiber and film materials. The interesting photomechanical deformation can be ascribed to the surface volume expansion caused by photoisomerization of azobenzene moieties. Then the photoinduced bending behaviors of these fibers containing different azobenzene concentrations and cross-linking densities were systematically investigated, suggesting that the location of photoresponsive azobenzene played an important role in deciding their photomechanical behaviors. This provides one convenient way of controlling over the photoinduced bending direction through the location of light-active moieties in side chain or cross-linker. In addition, irradiation of visible light accelerated the recovery of bent fibers. These fibers possess quick response, large deformation, and good thermal stability, indicating their promising applications for smart devices and energy conversion devices.

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

“…Moreover, the alignment direction of the mesogens can be spatially configured or patterned as homeotropic or twisted and in splay–bend, azimuthal or radial alignments, which endow the LCEs with complex shape morphing capabilities. Recently, monodomain liquid crystal elastomers or networks have been prepared by postphotocrosslinking or dynamic covalent bonding because of their improved processability. In addition, LCEs can be reshaped to form various 3D structures and achieve reversible complex 3D shape morphing or motion by reshaping dynamic 3D structures and via dynamic covalent bonds …”

A Light‐Activated Polymer Composite Enables On‐Demand Photocontrolled Motion: Transportation at the Liquid/Air Interface

“…In addition, the fast recovery process indicates that the deformation should be related to the dynamics of tans-to-cis and cis-to-trans isomerization rather than the trans/ cis ratio of azobenzene. [17] As ar esult, the photomechanical deformation could originate from the increase in molecular voids during the dynamic process,a nd eventually leads to macroscopic volume change as demonstrated by Barrett et al [17,18] After the removal of light, the dynamic isomerization processes stop and thermodynamic instability dictates the fast relaxation of free volume,and plays an important role in the deformation recovery.T oc onfirm this mechanism, photoinduced density changes were investigated. As shown in Figure S2 and Movie S1, the film in liquid floated upward upon UV irradiation and sunk as soon as light was switched off,a nd thus strongly supports the emergence of the photoinduced volume expansion.…”

Photomobile Polymer Materials with Complex 3D Deformation, Continuous Motions, Self‐Regulation, and Enhanced Processability

“…For a crosslinked polyacrylate system with modified concentration and location of azobenzene moieties, photoinduced stress was enhanced as much as 2.6 MPa . It is also proposed that the change in local volume along with the isomerization of azobenzene moieties plays a significant role in the deformation of CLCP samples …”