An Azoester-containing Photoresponsive Linear Liquid Crystal Polymer with Good Mesophase Stability

Recent Developments of Photodeformable Polymers: From Materials to Applications

Photodeformable polymer materials have a far influence in the fields of flexibility and intelligence. The stimulation energy is converted into mechanical energy through molecular synergy. Among kinds of photodeformable polymer materials, liquid crystalline polymer (LCP) photodeformable materials have been a hot topic in recent years. Chromophores such as azobenzene, α-cyanostilbene, and 9,10-dithiopheneanthracene have been widely used in LCP, which are helpful for designing functional molecules to increase the penetration depth of light to change physical properties. Due to the various applications of photodeformable polymer materials, there are many excellent reports in intelligent field. In this review, we have systematized LCP containing azobenzene into 3 categories depending on the degree of crosslinking liquid crystalline elastomers, liquid crystalline networks, and linear LCPs. Other structural, typical polymer materials and their applications are discussed. Current issues faced and future directions to be developed for photodeformable polymer materials are also summarized.

Three-dimensional liquid crystal polymer actuators assembled by athermal photo-welding

Photodeformable liquid crystal polymers (LCPs) exhibit shape changes of different modes like bending, twisting, and oscillation, which depend on the orientation of liquid crystals. However, it is challenging to create a three-dimensional (3D) actuator with distinct actuation modes due to the difficulty of local orientation in a complex bulk architecture. Here we propose a strategy based on athermal photo-welding to integrate different orientations into a single flexible actuator by the photofluidization of azobenzene-containing linear LCPs. Stretch-induced uniaxial films are cut in different directions and subsequently welded via local photofluidization, during which the LCP transitions from a high-modulus glassy state to a rubbery state upon photoisomerization of azobenzene at room temperature. As a consequence, a cucumber vine-like structure with the opposite handedness and a lifting gripper are constructed by such a cut-and-weld process, demonstrating diverse deformation modes of winding, unwinding, and curling. This strategy provides an athermal process for the fabrication of seamless 3D flexible actuators without structural defects, which have potential applications in micromechanical systems, soft robotics, and artificial muscles.

New Self-Organizing Optical Materials and Induced Polymorphic Phases of Their Mixtures Targeted for Energy Investigations

Herein, a new homologues series of fluorinated liquid crystal compounds, In, 4-(((4-fluorophenyl)imino)methyl)-2-methoxyphenyl 4-alkoxybenzoate were synthesized and its mesomorphic properties were investigated both experimentally and theoretically. The synthesized compounds were characterized by elemental analyzer, NMR, and FT-IR spectroscopy to deduce the molecular structures. The differential scanning calorimetry was employed to examine mesophase transitions whereas the polarized optical microscopy was used to identify the mesophases. The obtained results revealed that the purely nematic phase observed in all terminal side chains. All homologues showed to possess monotropic nematic mesophases except the derivative I8 exhibits enantiotropic property. The optimized geometrical structures of the present designed groups have been derived theoretically. The experimental data was explained using density functional theory computations. The estimated values of dipole moment, polarizability, thermal energy, and molecule electrostatic potential demonstrated that the mesophase stability and type could be illustrated. Binary phase diagram was constructed and addressed in terms of the mesomorphic temperature range and obtained polymorphic phases. It was found that incorporation of the terminal F-atom and lateral CH3O group influence both conformation and steric effect in pure and mixed states. The absorption and fluorescence emission spectra of fabricated films were recorded to elucidate the impact of terminal side chain on photophysical properties of synthesized liquid crystal. It was noted that the increase of terminal side chain length lead to reduction of optical band gap, whereas charge carrier lifetime increases.

Multi-photoresponsive triphenylethylene derivatives with photochromism, photodeformation and room temperature phosphorescence

A series of triphenylethylene derivatives exhibited multi-photoresponsive properties, including photochromism, photodeformation and room temperature phosphorescence (RTP), which are strongly related to molecular conformations and packing in the aggregated states. Accordingly, these properties can be subtly adjusted by substituents to the center double bond and/or peripheral phenyl moieties. The introduction of bromine atom was beneficial to photochromism and photodeformation properties as a result of the additional C-H⋯Br interactions and electron-withdrawing property. Also, it can promote the RTP effect via heavy atom effect, resulting in persistent afterglow lasting up to 150 min as detected by chemiluminescent imaging system.

Photodeformable Azobenzene-Containing Polyimide with Flexible Linkers and Molecular Alignment

Azobenzene-containing polyimides (azo-PIs) as photodeformable materials have attracted scientific attention in view of combining photoresponse and high performance (such as excellent mechanical and thermal properties). In the previously reported photodeformation of azo-PIs, polarized blue-green light was utilized to produce concerted motion of azobenzene moieties based on the mechanism of photoinduced reorientation. Herein, we explored a designed azo-PI undergoing photodeformation upon unpolarized light irradiation. The azo-PI film aligned by the hot-stretching process exhibited fast and reversible bending behavior under alternate ultraviolet (UV) and visible (vis) light irradiation, indicating the efficient nano-to-macroscopic propagation of molecular deformation of azobenzene. Besides, the aligned azo-PI film even bent in hot water (80 °C) and hot silicone oil (100 and 120 °C) with UV light irradiation.

Polymer Complex Fiber for Linear Actuation with High Working Density and Stable Catch-State

Fiber-based linear actuators (FLAs) are a key module in microrobots and biomimetic devices. It has been a great challenge to develop linear actuators that can balance output stress and output strain and hence provide high working density. Herein, we report the preparation and performance of a FLA system made from commercially available materials and allowed mass production at relatively low cost. The FLAs can lift up or lay down objects more than 1000 times of its own weight during active contraction and expansion under environmental stimuli. The contraction ratio and output stress can reach 30% and 0.24 MPa, respectively, and the sustainable work density is about 80 J/kg, which is 10 times the typical value of human skeletal muscles. Especially, the FLAs show stable catch-state (lock-up state) with no creeping and no further energy consumption.