Side-chain Liquid Crystalline Polymers Research Articles

Supramolecular Structure and Photo-Thermo-Electric Property of Hydrogen-Bonded Liquid Crystalline Polymer Containing Poly(4-vinylpridine) and Cyanostilbene Side Chains.

A series of side-chain liquid crystalline polymers P4VP(CN-DBE)x , where x is the molar ratio of cyanostilbene (CN-DBE) to poly(4-vinylpyridine) (P4VP) repeating unit, was synthesized based on the intermolecular hydrogen bonding between P4VP and CN-DBE. Their luminescent property, liquid crystalline structure and photo-thermo-electric property were elucidated using photoluminescence spectra, X-ray diffraction, thermal imaging and thermoelectric experiments. With the increase of x, the supramolecular system can be changed from lamellar structure to hexagonal columnar structure. Moreover, the P4VP(CN-DBE)x polymer with columnar structure exhibits more efficient photothermal effect. The temperature of P4VP(CN-DBE)0.6 can rise to 130 °C within 10 s under the irradiation of ultraviolet lamp. In addition, the supramolecular system possesses unique photo-thermo-electric conversion ability, and 25 mA current can be detected in the circuit coupled with the thermoelectric module. This work broadens the potential applications of hydrogen-bonded polymer, and provides a simple and facile strategy to prepare liquid crystalline polymers with photo-thermo-electric property.

Alignment Control of Smectic Layer Structures in Liquid-Crystalline Polymers by Photopolymerization with Scanned Slit Light.

Photoalignment control of hierarchical structures is a key process to enhance the properties of optical and mechanical materials. We developed an in situ molecular alignment method, where photopolymerization with the scanned slit light causes molecular flow, leading to two-dimensional precise alignment of molecules over large areas; however, the alignment control has been explored only on a molecular scale. In this study, we demonstrate this photopolymerization-induced molecular flow, enabling mesoscopic alignment of smectic layer structures composed of anisotropic molecules. Side-chain liquid-crystalline polymers were obtained from two different monomers with or without alkyl spacers by photopolymerization with one-dimensionally scanned slit light. The polymer with an alkyl spacer displayed mesogens aligned parallel to the scanning direction, while the polymer with no alkyl spacer resulted in perpendicular alignment of mesogens to the scanning direction, regulated by the alignment of the polymer main chain along the light scanning direction. Moreover, the polymerization with the scanned light aligned not only the mesogens but also mesoscopic smectic layer structures over large areas, depending on the structure and scanning pattern of light. We envision that such a simple polymerization technique could become a powerful and versatile alignment platform of anisotropic materials in a wide range of scales.

The Effect of a Topcoat with Amorphous Polymer Layers on the Mesogen Orientation and Photoalignment Behavior of Side Chain Liquid Crystalline Polymer Films

The mesogen orientations of liquid crystals are sensitive to the nature of the contacting surface. For side chain liquid crystalline polymer (SCLCP) films, most investigations have been conducted for thin films formed on a solid substrate surface such as glass, quartz and metal oxides, and little knowledge has been accumulated for SCLCP films whose top surface is covered by amorphous polymers. This work presents the effect of a topcoat with amorphous polymers placed on SCLCP films on the mesogen orientation and photoalignment behavior. When an SCLCP film that adopts a homeotropic mesogen orientation is covered with a glass plate or polymer layer, the mesogens turns to a random planar orientation. This planar orientation is favorable for efficient in-plane photoalignment by irradiation with linear polarized light. An in-plane order parameter exceeding 0.5 is readily obtained. Unexpectedly, a significant stabilization of the liquid crystal phase by over 10 °C is observed above the isotropization temperature of the SCLCP. These fundamental sets of knowledge should be significant in the fabrication of various polymer LC devices.

Synthesis and Phase Behavior of (Semifluorinated Alkane)-Based Side-Chain Liquid Crystalline Copolymers.

Side-chain liquid crystalline polymer (SCLCP) usually contains a simple and flexible homopolymer as main chain, while its effect on the self-assembly behavior is often ignored. In this work, in order to increase the structural complexity and investigate the interaction between the main chain and mesogens, perfluorinated segments are introduced into the main chain using a photoinduced Step Transfer-Addition & Radical-Termination polymerization method, producing a novel series of SCLCPs containing 4-methoxyphenyl benzoate mesogens, soft hydrocarbon spacers, and a strictly alternating perfluoroalkyl and alkyl backbone. By adjusting the length of spacers or perfluoroalkyl segments, several mesophases with complex chain packing structures are achieved. This design strategy that constructing highly ordered liquid crystalline (LC) structures from SCLCPs with precise chemical structure provides a facile way toward novel LC nanomaterials.

Experimental study on thermotropic side-chain liquid crystalline photo-sensitive polymers

When the chalcone moiety and methylene spacers are bonded to polymer backbone, they are expected to incorporate photosensitive and liquid crystalline properties, respectively. The thermotropic side-chain liquid crystalline photosensitive polymers were synthesized using 4-phenyl styryl carbonyl (phenyl-4-oxy-4-hexyl) methacrylate (PSCPOHMA) and 4-phenyl styryl carbonyl (phenyl-4-oxy-4-decyl) methacrylate (PSCPODMA) monomers by free-radical polymerization using benzoyl peroxide (BPO) as an initiator. The structures of the synthesized monomers and polymers were confirmed by FT-IR, 1H NMR and 13C NMR techniques. The thermal stability and glass transition temperature of the poly (PSCPOHMA) were higher than that of the poly (PSCPODMA). The photocrosslinking of the polymers on irradiation with UV light established that the polymers followed 2π + 2π cyclo addition. The rate of crosslinking increased with increase in the length of the methylene chain. The mesophase of the polymers was also characterized using x-ray diffraction analysis. The liquid crystalline behavior of the polymers was confirmed by DSC and Hot stage optical polarized microscopy (HOPM).The polymers exhibited nematic phase in HOPM. So the polymers have high potential for application in photo resists and electro optic technology.

Amphiphilic Liquid Crystalline Polymer Micelles That Exhibit a Phase Transition at Body Temperature

Liquid crystalline polymers (LCPs), which exhibit unique structures and properties intermediate between those of liquids and solids, are widely utilized as functional and advanced materials for fabricating optical devices and high-performance fibers. This utility stems from their ability to abruptly change their organized structures and mobilities at their liquid crystalline-isotropic phase transition temperatures, similar to the properties of biological membranes. Despite these numerous potential applications of LCPs, no study on their use in medical applications such as drug delivery has been reported. In the present study, we synthesized amphiphilic side-chain LCPs (LCP-g-OEGs, where OEG is oligo(ethylene glycol)) for medical applications, where the LCP-g-OEGs undergo a nematic-isotropic phase transition at body temperature. The LCP-g-OEGs formed micelles with a diameter of approximately 130 nm in aqueous media. The micelles were stable and did not dissociate in aqueous media even when the temperature exceeded the nematic-isotropic phase transition temperature (TNI). Although the release of a dye as a model drug from micelles was suppressed at temperatures lower than TNI, their dye release was drastically enhanced at temperatures higher than TNI. The LCP-g-OEG micelles regulated dye release reversibly in accordance with stepwise changes in temperature, without undergoing dissociation, differing from the behavior of standard temperature-responsive micelles. The temperature-responsive dye release behavior is induced by dramatic changes in their well-organized and dynamic structures as a result of the nematic-isotropic phase transition. These results demonstrate that the LCP-g-OEG micelles have a lot of medical applications as reversibly stimuli-responsive drug carriers.

Main-chain side-chain combined liquid crystalline polymers bearing azobenzene and biphenyl-based mesogens – segregation of the mesogens within two distinct layers

ABSTRACT Two different mesogenic units, namely biphenyl and azobenzene, were installed centrally within the polymer backbone and pendant alkylene segments; the purpose was to examine if chain folding of the backbone occurs so as to segregate the azobenzene and biphenyl units in adjacent layers of a smectic-type ordering. Two sets of isomeric main-chain side-chain liquid crystalline polymers (MCSC-LCPs), namely SC-AzoCx-MC-BPCx and SC-BPCx-MC-AzoCx (x=6 or 10), were synthesised; the former series has biphenyl in the backbone and azobenzene in the side-chain, while their locations are switched in the latter. It was observed that all four polymers were semicrystalline at room temperature and exhibited a smectic mesophase upon melting. DSC and X-ray scattering studies revealed that switching the locations of the azobenzene and biphenyls had little effect on; the phase transition temperatures and smectic layer spacings. A second series, namely SC-AzoCx-MC-BPCy and SC-BPCx-MC-AzoCy, where the length of alkylene spacers in the side-chain (Cx) and backbone (Cy) is different, was also studied; this was done to examine the influence of unequal alkylene segment lengths on the mesophase structure and interlayer spacing, and importantly, whether the zigzag folding-induced formation of a layered structure is retained, despite their unsymmetrical nature.

Correlation of self-assembly and thermal conducting properties of PEG-backbone polyether with a room temperature mesophase

A series of side chain liquid crystalline polymers with a cyanobiphenyl moiety was synthesized, and it showed considerably high thermal conductivity (∼0.46 W m−1 K−1) based on self-assembled microstructure developed by room temperature mesophase.

Photoswitchable Configuration of Nematic Liquid Crystal Droplets Embedded in a Honeycomb‐Patterned Film

AbstractHoneycomb‐patterned polymer films prepared by the breath figure method exhibit unique shape features. These films have potential in various applications, but functional materials are rarely embedded into the arrayed cavity. Here, a photoswitchable function of a compartmented nematic liquid crystal (NLC) in a honeycomb array is proposed. Surface segregation and liquid crystal self‐assembly processes cover curved honeycomb walls of polystyrene (PS) with a high‐density polymer brush of an azobenzene side chain liquid crystalline polymer (SCLCP), producing honeycomb polymer films with isolated cavities. Spherical confinement of the cavities with the SCLC brush provides a bipolar nematic director (planar anchoring), whereas UV light irradiation induces a radial configuration (homeotropic anchoring) of NLC droplets. Photoisomerization of azobenzene UV and visible light irradiation repeatedly induces a photoswitchable change between the bipolar and radial modes.

Competition of Lamellar Crystal and Smectic Liquid Crystal in Precise Polyethylene Derivative Bearing Mesogenic Side-Chains

For side-chain liquid-crystalline polymers (SCLCPs) bearing calamitic mesogens, nematic and typical smectic (Sm) phases are expected. Here, using a precise polyethylene derivative with the biphenyl...

Effect of local electric field on trans to cis photo-isomerization of azobenzene containing polymer

We report the effect of local electric field on the rate of photo-isomerization of azobenzene containing poly ethylene glycol-itaconate based side chain liquid crystalline polymer (PEGIA) in the ultra-thin film at air–water interface. The local electric fields were realised by adding polar polyvinylidene difluoride (PVDF) molecules in the PEGIA thin film. The ultra-thin film of PEGIA mixed with PVDF in different weight percentages were formed at air–water interface and are characterized using surface manometry technique. The rate constant of trans-cis photo-isomerization (k1) of azobenzene moieties in the presence of different amounts of PVDF were obtained from the surface pressure measurements. We find that the k1 exponentially increases with the percentage composition of PVDF which can be attributed to the effect of electric field due to the dipole moment of the PVDF molecules. The change in the activation energy of the photo-isomerization as a function of percentage composition of PVDF is calculated.

Effect of iron-iron oxide particles on the rate of isomerization of azobenzene moieties in polymeric liquid crystals at air-water interface

We have studied the effect of iron-iron oxide particles on the trans-cis isomerization of azobenzene moieties in the novel polyethylene glycol itaconate-azobenzene based side chain liquid crystalline polymer (PEGIA). Langmuir monolayers of the PEGIA molecules are spread at air-water interface, with water subphase containing different concentrations of iron-iron oxide particles. The kinetics of the isomerization of azobenzene moieties in the polymer was studied by surface manometry technique. We find that the presence of iron-iron oxide particles in the subphase affects the rate constant of trans-cis photoisomerization and it decreases exponentially as a function of concentration of particles in the subphase. The critical concentration of iron-iron oxide particles above which the rate constant of photoisomerization negligibly changed was found to be about 2.468 μg cm− 3.

Initiation of RAFT Polymerization: Electrochemically Initiated RAFT Polymerization in Emulsion (Emulsion eRAFT), and Direct PhotoRAFT Polymerization of Liquid Crystalline Monomers

We report on two important advances in radical polymerization with reversible addition–fragmentation chain transfer (RAFT polymerization). (1) Electrochemically initiated emulsion RAFT (eRAFT) polymerization provides rapid polymerization of styrene at ambient temperature. The electrolytes and mediators required for eRAFT are located in the aqueous continuous phase separate from the low-molar-mass-dispersity macroRAFT agent mediator and product in the dispersed phase. Use of a poly(N,N-dimethylacrylamide)-block-poly(butyl acrylate) amphiphilic macroRAFT agent composition means that no added surfactant is required for colloidal stability. (2) Direct photoinitiated (visible light) RAFT polymerization provides an effective route to high-purity, low-molar-mass-dispersity, side chain liquid-crystalline polymers (specifically, poly(4-biphenyl acrylate)) at high monomer conversion. Photoinitiation gives a product free from low-molar-mass initiator-derived by-products and with minimal termination. The process is compared with thermal dialkyldiazene initiation in various solvents. Numerical simulation was found to be an important tool in discriminating between the processes and in selecting optimal polymerization conditions.

Photo-triggered large mass transport driven only by a photoresponsive surface skin layer

Since the discovery 25 years ago, many investigations have reported light-induced macroscopic mass migration of azobenzene-containing polymer films. Various mechanisms have been proposed to account for these motions. This study explores light-inert side chain liquid crystalline polymer (SCLCP) films with a photoresponsive polymer only at the free surface and reports the key effects of the topmost surface to generate surface relief gratings (SRGs) for SCLCP films. The top-coating with an azobenzene-containing SCLCP is achieved by the Langmuir–Schaefer (LS) method or surface segregation. A negligible amount of the photoresponsive skin layer can induce large SRGs upon patterned UV light irradiation. Conversely, the motion of the SRG-forming azobenzene SCLCP is impeded by the existence of a LS monolayer of the octadecyl side chain polymer on the top. These results are well understood by considering the Marangoni flow driven by the surface tension instability. This approach should pave the way toward in-situ inscription of the surface topography for light-inert materials and eliminate the strong light absorption of azobenzene, which is a drawback in optical device applications.

A Novel Side-Chain Liquid Crystal Elastomer Exhibiting Anomalous Reversible Shape Change.

Liquid crystalline elastomers (LCEs) have been actively investigated as stimuli-controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)-isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side-chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC-disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side-group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit.

A Novel Side‐Chain Liquid Crystal Elastomer Exhibiting Anomalous Reversible Shape Change

AbstractLiquid crystalline elastomers (LCEs) have been actively investigated as stimuli‐controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)‐isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side‐chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC‐disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side‐group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit.

Fabrication of re-shapeable liquid crystalline elastomers with dynamic C–N bonds and investigation of their reversible photoresponsive bending behaviors

<p indent=0mm>Liquid crystalline elastomers (LCEs) spontaneously change their dimensions and shapes in response to external stimuli, such as heat or light irradiation; however, LCEs based on conventional covalent crosslinks are thermosetting materials and thus unable to remold or fabricate into complex three-dimensional (3D) soft actuators. In this work, we prepared polysiloxane side-chain liquid crystalline polymers with both <italic>p</italic>-methoxyphenyl benzoate (PB) and azobenzene (Azo) mesogens introduced as side groups through thiol-ene click reaction. Then a monodomain liquid crystalline elastomer LCE-M film was fabricated by fixing the macroscopic alignment of mesogens induced by uniaxial stretching upon heating to a higher temperature through C–N dynamic covalent bonds via highly efficient transalkylation between alkyl bromide and triazole from azide-alkyne click reaction to achieve rearrangement and regeneration of the crosslinked networks. The introduction of Azo mesogen with <italic>trans</italic>-<italic>cis</italic> isomerization characteristics endowed the LCE-M thin films with reversible photoresponsive deformation properties of bending-stretching recovery upon alternate irradiation of UV and visible light. With the separation of alignment method and driving mode of such liquid crystalline elastomer material, the monodomain liquid crystalline elastomer LCE-M thin films can be repeatedly and stably driven by light irradiation at room temperature, which is expected to be employed for the fabrication of reshapeable flexible LCE actuators with faster photo response.

Induction of Highly Ordered Smectic Phases in Side Chain Liquid Crystalline Polymers by Means of Random Copolymerization

The glass transition and melting temperatures of binary random copolymers are mostly observed as nearly the average of each homopolymer with moderate deviations. However, copolymerization of binary...

Phase Structure Recording in a Nematic Side-Chain Liquid-Crystalline Polymer.

Dye-doped nematic side-chain liquid-crystalline polymers possess extraordinary large optical nonlinearity and ability to store the induced orientational deformations in a glassy state, which makes them a very promising material for photonic applications. In this study, the phase structures were generated and recorded in the bulk of a 50-μm layer of a nematic liquid-crystalline side-chain polymer, containing polyacrylate backbone, spacer having five methylene groups, and phenyl benzoate mesogenic fragment. The polymer was doped with KD-1 azodye. The director field deformations induced by the light beam close to the TEM01 mode were studied for different geometries of light–polymer interaction. The phase modulation depth of 2π was obtained for the 18-μm spacing between intensity peaks. The experimental data were analyzed based on the elastic continuum theory of nematics. The possibility to induce and record positive and negative microlenses in the polymer bulk was shown experimentally.

Preparation, performances and applications of multi-functional photoluminescence form-stable phase change materials

Up to now, most of the reported phase change materials only show a single application in thermal energy storage and can not satisfy the increasing demand for multifunctional materials. In this study, we first designed and prepared a novel multi-functional photoluminescence form-stable phase change materials (FSPCMs) using photoluminescence side chain liquid crystalline polymers with different flexible spacers length as gelators, and using paraffin as phase change materials. The properties, and the effect of flexible spacer length on the properties of photoluminescence FSPCMs were studied in detail by “tube test” method, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier-transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), rheometry test, ultraviolet spectroscopy (UV) and photoluminescence instruments (PL). Experiment results showed that the prepared photoluminescence FSPCMs showed high thermal energy storage density and solid fluorescence quantum yield. The phase transition enthalpy for our prepared photoluminescence FSPCMs can reach 193.1 J g−1 and the solid fluorescence quantum yield can achieve 16.54%. The prepared photoluminescence FSPCMs can also absorb UV light and can be used as UV shielding materials. The properties of photoluminescence FSPCMs varied with the spacer length of polymer gelators. With increasing spacer length, the thermal stability and mechanical property of prepared photoluminescence FSPCMs showed the trend of deterioration. However, the solid fluorescence quantum yield of them increased with the increasing spacer length of polymer gelators.