Azobenzene Liquid-crystalline Polymer Research Articles

Dual-Regulation of Supramolecular Chirality in Achiral Side-Chain Azobenzene Liquid-Crystalline Polymers.

Azobenzene (Azo) liquid-crystalline polymers are intriguing due to their unique photo-induced isomerization and supramolecular chirality. However, clarification on multicomponent chiral induction towards Azo polymers remains ambiguous and challenging. Herein, chiral solvents and amines were employed to control the chiroptical activity of achiral Azo polymers. Methyl L-/D-lactate was added as the poor solvent and chiral inducer to achieve the first chiral induction in Azo aggregates. Chiral amines were utilized for the second chiral induction based on the acid-base interactions between the carboxyl groups of polymers and amines. The chiral enhancement and inversion of Azo units could be observed through the synergistic or antagonistic effect between solvents and amines. The impacts of solvent, chemical structures, feed ratio, enantiomeric excess, and temperature on supramolecular chirality were systematically studied. Furthermore, this system displayed the chiroptical switching property and chiral recovery under reversible irradiation.

Non-volatile optical memory based on cooperative orientation switching: improvement of recording speed and contrast by utilizing out-of-plane orientation mode.

Herein, we report a novel strategy toward non-volatile optical memory with high-contrast, high-speed recording, and non-destructive readout capability based on the cooperative out-of-plane orientation of a fluorescent dye doped into azobenzene liquid crystalline polymer film. By employing the out-of-plane orientation switching upon irradiation with UV light and thermal heating, high-contrast turn-on fluorescence switching was successfully achieved and the optical recording was demonstrated with non-destructive fluorescence readout capability. Furthermore, the recording speed and the fluorescence on/off contrast in the present system were dramatically improved compared to the previous in-plane orientation mode.

Shape programming and photoactuation of interpenetrating polymer networks containing azobenzene moieties

The shape memory effects and photoinduced deformation behaviour of interpenetrating polymer network (IPN) films containing azobenzene liquid-crystalline polymers were investigated.

Synthesis and phase behaviour of a class of comb-like cholesteric azobenzene liquid crystalline polymers

ABSTRACT In this paper, we designed and synthesised two azo liquid crystal monomers (M1 and M2) and a chiral liquid crystal monomer N, followed by side-chain graft copolymerisation with polymethylhydrosiloxane (PMHS) to synthesize comb-like liquid crystalline polymers PN1 and PN2. The structures of all liquid crystal monomers and polymers conform to the molecular designs by FT-IR and 1H NMR. The liquid crystal properties were tested by DSC and POM, and the results showed that M1 and M2 were thermotropic enantiotropic nematic liquid crystals and N was a thermotropic enantiotropic cholesteric liquid crystal. Both the PN1 and PN2 series were amorphous polymers. The PN1 and PN2 series exhibited a typical Grand-jean texture. The glass transition temperature and isotropic temperature of the PN1 and PN2 series decreased first and then increased with the increase of azo monomer M content. And the glass transition temperature and isotropic temperature of the PN1 series were higher than the PN2 series. Both the PN1 and PN2 series had good thermal stability. The mesophase range of the PN1 series was 173.5°C~181.5°C, and the PN2 series was 162.5°C~172.9°C.

Liquid crystallinity and thermal properties of polyhedral oligomeric silsesquioxane/side-chain azobenzene hybrid copolymer

Abstract Acrylic acid-modified polyhedral oligomeric silsesquioxane (AC-POSS) was synthesized by the reaction between the amine groups in polyhedral oligomeric silsesquioxane (POSS) and acrylic acid, which could dissolve in water and can be easily purified. Free-radical copolymerization was applied to synthesize azobenzene liquid crystalline polymer silsesquioxane (LCP-POSS) with different proportions of AC-POSS and liquid crystalline monomers. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing ultraviolet irradiation time. The photoisomerization reaction of liquid crystalline polymer (LCP) and LCP-POSS showed the first-order dynamic reaction. Compared with the LCP, the photoisomerization rate constant of LCP-POSS was decreased due to the space steric hindrance of the POSS as a rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increased with increasing POSS content, and the liquid crystalline texture in LCP-POSS became smaller under the polarized light. With further increasing the POSS content (>50 wt%) in LCP-POSS, the ordered structure of the liquid crystalline phase was gradually affected, resulting in one-way liquid crystal (LC) phase behavior. The synthesized LCP-POSS has LC properties, light-responsive properties, and thermal stability. When the POSS is introduced into the LC material, the phase state of the LC material will become more abundant and the LC phase will become more stable. The significance of this study is to develop and extend its applications as stimuli-responsive materials and devices.

Remolding of Photoresponsive Polymer Materials by Means of Dynamic Covalent Bonds In a Main Chain

We prepared crosslinked azobenzene main-chain liquid-crystalline polymers (MCLCPs), in which the exchange of crosslinks can be brought about by transesterification reactions. The exchangeable crosslinks enable reshaping and self-healing of the MCLCPs upon heating. Furthermore, the stress generated by stretching the MCLCP film is completely relaxed at 180 °C through rearrangement of networks. The film after hot-drawing shows reversible bending behavior upon irradiation with UV and visible light.

Photoinduced deformation and isomerization of azobenzene liquid-crystalline polymer films at cryogenic temperature

We prepared 2 types of crosslinked liquid-crystalline polymers (CLCPs) (polyacrylates) with the same side-chain length but a different position of an azobenzene moiety in the side chain. We evaluated photoinduced deformation behavior of the CLCP films and photoisomerization behavior of azobenzene in the films at cryogenic temperature. Azobenzene moieties in both CLCP films showed no trans-cis isomerization and neither film exhibited bending behavior upon irradiation with UV light in liquid nitrogen [77 K]. On the other hand, when the film included azobenzene with a long spacer and a short tail, cis-trans isomerization of azobenzene and photoinduced deformation were observed in liquid nitrogen.

Fabrication of photomobile polymer materials with phase-separated structure of crosslinked azobenzene liquid-crystalline polymer and poly(dimethylsiloxane)

ABSTRACTComposite systems of liquid crystals (LCs) and polymers have been extensively studied in various forms such as polymer-dispersed LCs and polymer-stabilised LCs. Blending LCs and polymers is an effective approach to design functional materials with stimuli responsiveness and durability. Here, we show the development of a novel composite material with crosslinked azobenzene LC polymer (PAzo) and poly(dimethylsiloxane) (PDMS) aiming at the improvement of photomobile polymer materials in mechanical properties. The composite films were prepared by photopolymerisation of azobenzene monomers in PDMS elastomers. By forming phase separated structure, in which PAzo chains were dispersed in PDMS matrix, fracture strain of photomobile polymer materials was significantly enhanced. The composite film showed macroscopic bending upon irradiation with UV light. This result implies that PAzo domains in polymer matrix can work as microactuators to afford macroscopic deformation of the whole film. The further improvement of this system in photomechanical properties would be feasible through adequate control of composition and the alignment of mesogens.

Photo-modulations of surface wrinkles formed on elastomer sheets

ABSTRACTSurface wrinkle formation is ubiquitous in nature, and has become of great importance from the technological viewpoints of surface patterning and fabrications. To date, most of studies on the surface wrinkle formation have been achieved with surface thin films of fixed physical properties formed by deposition or lamination on elastomeric sheets such as poly(dimethyl siloxane) films. This article introduces our recent results on tunable surface wrinkle formation in response to light using azobenzene-containing liquid crystalline polymers. Two strategies are proposed: i) anisotropic wrinkle formation using a photoalignable radical initiator in UV-curable liquid crystal films, and ii) modulations of wrinkle formation using a series of azobenzene liquid crystalline polymers.

3C01 エステル交換反応による動的共有結合性架橋アゾベンゼン液晶高分子の創製(液晶フォトニクス・光デバイス,口頭発表,2015年日本液晶学会討論会)

3C01 エステル交換反応による動的共有結合性架橋アゾベンゼン液晶高分子の創製(液晶フォトニクス・光デバイス,口頭発表,2015年日本液晶学会討論会)

PA48 極低温における架橋アゾベンゼン液晶高分子の光運動プロセス(液晶フォトニクス・光デバイス,ポスター発表,2015年日本液晶学会討論会)

PA48 極低温における架橋アゾベンゼン液晶高分子の光運動プロセス(液晶フォトニクス・光デバイス,ポスター発表,2015年日本液晶学会討論会)

Interpenetrating polymer networks of liquid-crystalline azobenzene polymers and poly(dimethylsiloxane) as photomobile materials.

We developed photomobile polymer materials with interpenetrating polymer network (IPN) structures composed of crosslinked liquid-crystalline azobenzene polymer (PAzo) and poly(dimethylsiloxane) (PDMS). By introducing PDMS into a PAzo template network, IPN was formed without disturbing the alignment of mesogens in the PAzo network. The films showed macroscopic bending behavior upon irradiation with UV and visible light. Although the IPN film showed a phase separated structure, the bending speed was significantly enhanced compared with the pristine film of PAzo, thanks to the soft nature of PDMS. The present method of preparing IPNs can be a promising approach to combine PAzo with various polymers and enhance the mechanical and photoresponsive properties.

Photo-responsive polysiloxane-based azobenzene liquid crystalline polymers prepared by thiol-ene click chemistry

ABSTRACTIn this work, a novel polysiloxane-based azobenzene-containing liquid crystalline polymer (LCP) PMMS-A44V6 has been designed and synthesized via a facile thiol-ene click chemistry method by grafting a side-on azobenzene mesogenic group A44V6 onto poly-[3-mercaptopropylmethylsiloxane] (PMMS) backbone. 1H NMR, 13C NMR, GPC, TGA, DSC, POM and WAXS were used to investigate the mesogenic properties and photo-responsive behaviour of PMMS-A44V6. Taking advantage of the azobenzene’s trans–cis isomerization effect, PMMS-A44V6 can perform an isotropization process under UV irradiation in its nematic phase. Initially, the isotropization process starts in a linearly decreasing manner with a rate of ca −6.5 × 105 intensity/s, and eventually finishes in an exponential decrease regime to form cis-azobenzene moieties. The reversible UV-response behaviour of PMMS-A44V6 can be performed in a relatively low temperature range of 30 ~ 75°C, which might help this azobenzene-containing LCP material to find potential application in control devices.

Photomobile materials with interpenetrating polymer networks composed of liquid-crystalline and amorphous polymers

Interpenetrating polymer networks composed of a crosslinked azobenzene liquid-crystalline polymer and poly(alkyl methacrylate)s were developed to enhance the photoresponsive and mechanical properties of photomobile polymer materials.

Polarization-controlled images based on double-exposure polarization holography in an azobenzene liquid-crystalline polymer.

Polarization-controlled optical image operations were demonstrated based on the double-exposure polarization holographic method. Two images were stored in the same volume of an azobenzene liquid-crystalline polymer by recording superimposed holograms, a pair of polarization gratings with one spatial frequency, using two orthogonal circularly polarized 532nm beams and were reconstructed with a 650nm laser. The recorded polarization holographic gratings were investigated to show distinctive polarization selectivity, high diffraction efficiency, and good stability. The brightness and the polarization of the diffracted images were found to be dependent on the polarization of the readout beam, and two images could be reconstructed individually or simultaneously.

Synthesis and Characterization of Azobenzene Liquid Crystalline Polymers Containing Cholesteryl Groups

Synthesis and Characterization of Azobenzene Liquid Crystalline Polymers Containing Cholesteryl Groups

Free Surface-Induced Planar Orientation in Liquid Crystalline Block Copolymer Films: On the Design of Additive Surface Active Polymer Layer

We recently demonstrated that addition of a surface active polymer (SAP) that segregates on the free (air) surface in liquid crystalline (LC) block copolymer films crucially alters the orientation of the mesogens and microphase separation domains. A block copolymer of poly(butyl methacrylate) (PBMA) combined with an azobenzene LC polymer has been blended as SAP in a polystyrene-based LC block copolymer films possessing similar structure. The present work reveals that the polymer design, the blend ratio, and molecular weight of the surface active polymer significantly affect the orientational alternation for the block copolymer film. The orientational alternation effect by the free surface segregation becomes significantly efficient when SAPs with higher molecular weight is employed.

Photomobile Polymer Materials with Double Network Structures: Crosslinked Azobenzene Liquid-Crystalline Polymer/Methacrylate Composites

We prepared photomobile polymer materials composed of crosslinked azobenzene liquid-crystalline polymers (LCPs) and methacrylates with interpenetrating polymer network (IPN) structures, and explored their photoresponsive behavior. The IPN films exhibited reversible bending upon photoirradiation. In addition, the durability of the IPN films was much higher than that of the pristine crosslinked azobenzene LCP films.

Photomobile Properties of Interpenetrating Polymer Network Films Composed of Azobenzene Liquid Crystalline Polymer and Polymethacrylates

Various fabrication methods of photomobile polymer materials containing photochromic moieties have been developed to improve their photoresponsive and mechanical properties. Here, we newly prepared photomobile polymer materials with interpenetrating polymer network (IPN) structures. The IPN films, which are composed of azobenzene liquid crystalline polymer (LCP) and polymethacrylates, showed reversible bending behavior upon exposure to UV and visible light. Bending speed of the IPN films became higher with decreasing glass-transition temperature of polymethacrylate components. The IPN film containing poly(dodecyl methacrylate) showed faster bending than the pristine azobenzene LCP film.

Photoinduced bending behavior of cross-linked azobenzene liquid-crystalline polymer films with a poly(oxyethylene) backbone.

Cross-linked azobenzene liquid-crystalline polymer films with a poly(oxyethylene) backbone are synthesized by photoinitiated cationic copolymerization. Azobenzene moieties in the film surface toward the light source are simultaneously photoaligned during photopolymerization with unpolarized 436 nm light and thus form a splayed alignment in the whole film. The prepared films show reversible photoinduced bending behavior with opposite bending directions when different surfaces of one film face to ultraviolet light irradiation.