Side-chain Liquid Crystalline Polymers Research Articles

Alignment Control of Nematic Liquid Crystal using Gold Nanoparticles Grafted by the Liquid Crystalline Polymer with Azobenzene Mesogens as the Side Chains.

The gold nanoparticles highly grafted by a liquid crystalline polymer (LCP) with azobenzene mesogens as the side chain (denoted as Au@TE-PAzo NPs) are successfully designed and synthesized by the two-phase Brust-Schiffrin method. The chemical structures of the monomer and polymer ligands have been confirmed by nuclear magnetic resonance, and the molecular weight of the polymer is determined by gel permeation chromatography. The combined analysis of transmission electron microscopy and thermogravimetric analysis shows that the size of the nanoparticles is 2.5(±0.4) nm and the content of the gold in the Au@TE-PAzo NPs is ca. 17.58%. The resultant Au@TE-PAzo NPs can well disperse in the nematic LC of 5CB. The well-dispersed mixture with appropriate doping concentrations can automatically form a perfect homeotropic alignment in the LC cell. The homeotropic alignment is attributed to the brush formed by Au@TE-PAzo NPs on the substrate, wherein the Au@TE-PAzo NPs gradually diffuse onto the substrate from the mixture. On the contrary, the pure side chain LCPs cannot yield vertical alignment of 5CB, which indicates that the alignment of 5CB is ascribed to the synergistic interaction of the nanoparticles and the grafted LCPs. Moreover, Au@TE-PAzo NPs show excellent film-forming property on account of their periphery of high densely grafted LCPs, which can form uniform thin film by spin-coating. The resultant thin film also can prompt the automatical vertical alignment of the nematic 5CB. Further, upon alternative irradiation of UV and visible light, the alignment of 5CB reversibly switches between vertical and random orientation because of the trans-cis photoisomerization of the azobenzene group on the periphery of Au@TE-PAzo NPs. These experimental results suggest that this kind of nanoparticles can be potentially applied in constructing the remote-controllable optical devices.

Surface and interface designs in side-chain liquid crystalline polymer systems for photoalignment

In side-chain liquid-crystal (SCLC) polymer systems, the liquid crystalline (LC) mesogenic groups preferentially orient normal to the substrate plane due to the excluded volume effect (homeotropic alignment). Photoresponsive azobenzene (Az) mesogens have a transition moment parallel to the molecular long axis. Light irradiation for photoreactions is generally applied perpendicular to the film surface. Therefore, a homeotropic orientation inhibits efficient photoreactions and photoalignments in Az SCLC polymer systems. This review focuses on new approaches to induce a random planar orientation in Az SCLC polymer systems by interface and surface molecular design. The mesogens in a high-density SCLC polymer brush formed by surface-initiated living radical polymerization adopt a random planar orientation. In the film of an SCLC block copolymer with an amorphous block, a random planar orientation is induced via surface segregation of either of the blocks. The random planar orientations of SCLC polymer systems are thermally stable and offer efficient in-plane photoalignment and photoswitching with hierarchical LC molecular architectures, forming, e.g., microphase-separated (MPS) SCLC block copolymers and layered polymer LC systems. These surface and interface molecular designs are expected to provide new concepts and possibilities for LC polymer devices. The liquid crystalline (LC) rod-like mesogens preferentially orient normal to the substrate plane due to the excluded volume effect (homeotropic alignment) in side-chain liquid-crystal (SCLC) polymers free-standing films. For in-plane alignment, a homeotropic orientation is unsuitable because the mesogens are in a direction opposite to the in-plane directions. This review focuses on new approaches to induce a random planar orientation in SCLC polymer systems by interface and surface molecular design utilizing a high-density polymer brush structure and surface segregation structures of block copolymers.

Synthesis of novel core-shells of PMMA with coumarin based liquid crystalline side chains and PMMA shell as electro-optical materials

The synthesis and electro-optical properties of novel side-chain liquid crystalline polymers (SCLCPs) is described. The polymers were liquid crystalline polymers with mesogenic coumarin based side groups separated from the poly (methyl methacrylate) backbone by flexible alkyl spacers of varying lengths. The effect of the flexible spacer length on the phase properties and electric field effects as well as effect of polymer structure on the electro-optical properties of liquid crystalline polymers is investigated. Considering the results of analysis such as DSC and POM, the sample with longer spacer length and more liquid crystal properties was subjected to further characterizations. The particles of sample with longer spacer was covered with a PMMA shell of different thicknesses and their electro-optical properties were studied showing an 80% of change in transmittance by change of applied potential from 0 to 14 V. To the best of our knowledge this is the first study in its kind on this type of structures.

Polarization modulation by means of tunable polarization gratings in an azobenzene side-chain liquid-crystalline polymer film.

Polarization modulation was achieved by means of a new type of grating recorded with two 532nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged. With the polarization angle changing from 0 to 90deg, the ± first-order diffraction efficiency increased from 5.15% to 10.53%. Diffraction properties of the recorded gratings were attributed to the combination of polarization holographic gratings and amplitude gratings based on the calculation of Jones matrices and polarization holographic theory.

High performance liquid crystalline physical gels prepared by side chain liquid crystalline polymers

Liquid crystalline physical gels (LCPGs) with stable mechanical properties and fast electro-optical response properties were prepared through the self-assembly of side chain liquid crystalline polymers (SCLCPs) with different spacer length poly [ω-4′-cyano-(1, 1′-biphenyl)] acrylate (PmACB, m is the spacer length of SCLCP, m = 0, 2, 4) as gelators in a nematic liquid crystal, 4-pentyl-4′-cyanobiphenyl (5CB). The gel-sol phase transition temperature (TGS), micro morphology, mechanical properties and electro-optical properties of LCPGs (SCLCPs/5CB) were systematically studied. The results show that only P0ACB can form stable liquid crystalline physical gels in 5CB and show excellent thermal stability, good self-supporting ability and fast electro-optical response properties. The TGS of 6 wt% P0ACB/5CB gel is 192 °C, and it also showed stable mechanical properties, its storage modulus is about 1.0 × 104 Pa. The threshold voltage (Vth) and saturation voltage (Vsat) of P0ACB/5CB gel with 3 wt% concentration are 0.29 V μm−1and 3.906 V μm−1 respectively, and the off state response time is only 6.748 ms. Moreover, the addition of the polymer does not affect the electro-optical response of the LCPGs.

Multiple Effects Tailoring the Self-organization Behaviors of Triphenylene Side-chain Liquid Crystalline Polymers via Changing the Spacer Length

Long-alkyl tail triphenylene (TP) side-chain liquid crystalline polymers (SCLCPs) with different spacer length (P-m-TP, m = 2, 3, 4, 6, 8, which is the number of carbon atom in the flexible alkyl spacers) have been successfully synthesized via free radical polymerization. The differential scanning calorimetry (DSC), polarized light microscopy (POM), ultraviolet-visible spectroscopy (UV-Vis), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements were performed to investigate the influence of multiple effects on the self-organization behaviors of P-m-TP, including steric effect, decoupling effect and π-π stacking effect. The experimental results revealed that P-m-TP (m = 2, 3, 4) formed the columnar phase which was developed by the TP moieties and the main chain as a whole, suggesting that the side-chains had strong steric effect even though the number of spacer length (m) exceeded 4. In addition, the clearing points (Tis) of the polymers were above 300 °C. When m = 6 and 8, the polymers displayed hexagonal columnar phase and exhibited the low Tis (91 and 80 °C respectively), originating from the self-assembly of triphenylene due to the decoupling effect and π-π stacking effect. This work offers a viable and inspiring pathway to control the phase transition temperature and phase structure of TP SCLCPs via simply tailoring the spacer length and increasing the alkyl tail length of TP.

Photocontrol of mesogen alignment in a side chain LC polymer film by means of random copolymerization of two mesogens of opposing orientation nature

ABSTRACTIn general, photoreorientive azobenzene (Az) mesogens in side chain liquid crystalline polymers (SCLCPs) adopt a homeotropic orientation in a thin film state, which can be a drawback for the azimuthal photoalignment. We report herein a SCLCP that shows a planar orientation of Az mesogen achieved by random copolymerization with a planarly orienting cyanobiphenyl (CB) mesogen. Using this planarly orienting SCLCP film, a homogeneous in-plane orientation can be readily achieved by irradiation with linearly polarized light, and further a metastable homeotropic orientation is attained by normal irradiation by non-polarized light. Thus, 3D mesogen alignment controls are achievable on demand. We propose here the utility of the random copolymerization strategy to extend the possibility of photoalignment procedures.

Preparation and properties of side chain liquid crystalline polymers with aggregation-induced emission enhancement characteristics

A series of polymers with aggregation-induced emission enhancement characteristics and stable liquid crystalline properties were prepared.

Novel application of a classical side-chain liquid crystalline polymer as a gelator for common solvents

A classical side-chain liquid crystalline polymer (SCLCP) named poly [ω-(4′-n-octadecyloxybiphenyl-4-oxy) hexyl methacrylate (PM6BiC18) have been synthesized. The polymer and its monomer (M6BiC18) organogels were prepared by introducing PM6BiC18 or M6BiC18 into common organic solvents. The minimum gelation concentration (MGC) and gel-to-sol transition temperature (TGS) were tested by the “tube-testing method”. In the same organic solvent, it was found that the TGS of gels based on PM6BiC18 was higher than the gels formed by M6BiC18. The microscopic morphology of the gels was carefully investigated by SEM and polarizing microscope. Experimental results revealed that the M6BiC18 gels are formed by the crystallization of fibers. However, the polymer gels are formed by uniform spherical self-assembly structures. Further studies discussed by UV–vis spectroscopy, the results implied that the π–π stacking interaction of the biphenyl mesogens might be the key factor for guiding the self-assembly processes and the polymer gel formation.

Functional liquid-crystalline polymers and supramolecular liquid crystals

The design and functions of liquid-crystalline (LC) polymers with classifying them into conventional-, supramolecular-, dendritic- and network-type LC polymers are described. LC polymers show new functions as new devices in the field of energy and environment by incorporating mesogenic moieties exhibiting photonic, electronic and ionic functions. Supramolecular LC polymers show dynamic and unique properties because the mesogenic moieties are built with non-covalent interactions. Dendritic-type LC polymers exhibit liquid crystallinity by nanosegregation of aromatic and aliphatic moieties. Dendritic fork-like mesogens have also been prepared. A variety of nonmesogeic functional building blocks including fullerene, π-conjugated moieties, catenane, rotaxane and others can be incorporated into LC phases by attaching these dendritic moieties. LC networks are constructed in situ polymerization of polymerizable nematic or nanostructured liquid crystals. The specific characteristics of the LC networks have generated new research trends to develop well-defined polymers that exhibit optical, transport and separation properties. In these materials, through suitable design of LC monomers, the preservation of smectic, columnar and bicontinuous cubic phases has been successfully used for the development of membranes with one-dimensional, two-dimensional and three-dimensional nanostructures. The design and functions of various liquid-crystalline (LC) polymers including main-chain, side-chain and network LC polymers as well as dendritic structures are described. These polymeric LC materials can be applied for electro-, ion-, photo-active materials as well as mechanically tough materials. The introduction of supramolecular design has also generated a new category of functional LC materials.

Methacrylate based side chain liquid crystalline polymers with pendant cholesterol group: Preparation and investigation of electrical conductivity mechanism

ABSTRACTMethacrylate based side‐chain liquid crystalline polymers (SCLCP) bearing cholesterol pendant moieties with various lengths of aliphatic spacer were synthesized and their electrical conductivity mechanism was studied for their possible applications in elastic microelectronic devices. All the polymers exhibited liquid crystalline behavior of broken focal‐conic fan texture of smectic phase. The dielectric properties of polymers were investigated by impedance spectroscopic technique in the frequency range of 100 Hz to 15 MHz at room temperature. Alternating current (AC) conductivity ( ) of the liquid crystalline polymeric films was observed to vary with angular frequency, ω as ωS with s < 2. Detailed conductivity analysis revealed that the conductivity of the polymeric films follows quantum mechanical tunneling and correlated barrier hoping conductivity mechanisms at low frequency regime, whereas it obeys super linear power law and direct current conductivity mechanisms at high frequency region. The investigation of the SCLC polymeric films helped to propose a model system for their possible potential applications. In the light of this study, the SCLC polymers will be employed as the gate insulator for organic field effect transistor applications, such as large area flexible arrays or as other advanced microelectronic devices that have superior performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45207.

Self-Assembly Behavior of Triphenylene-Based Side-Chain Discotic Liquid Crystalline Polymers

We constructed a generic coarse-grained model of triphenylene-based side-chain discotic liquid crystalline polymers (SDLCPs). Then dissipative particle dynamics (DPD) simulation was employed to systematically study how composition and structural factors of SDLCPs such as molecular weight, main chain, spacer and aliphatic tails, and the incompatibility between mesogenic core and its substituents influence their mesophases and self-assembly behavior. Eight mesophases were obtained by changing the factors mentioned above. The eight phases are hexagonal columnar–amorphous (Colh-Am), nematic columnar–amorphous (Colne-Am), nematic columnar–clustered (Colne-Clu), nematic columnar–columnar (Colne-Col), random columns–amorphous (Colran-Am), random columnar–clustered (Colran-Clu), amorphous–amorphous (Am-Am), and sphere–amorphous (Sph-Am). The name of mesophase is denoted as “assembly of discogens-aggregation of backbone”. By checking conformation of molecules, the intracolumnar self-assembling patterns based on the discrete columnar stack (DCS) were observed in Colh-Am, Colne-Am, and Colne-Clu, while Colne-Col and Sph-Am adopted different packing modes. Moreover, molecular weight effect and positive coupling of spacer were discolosed, which matches well with experiments. Moderate or strong incompatibility between mesogenic cores and substituents and proper peripheral aliphatic tails are needed for SDLCPs to form ordered mesophases. The in-depth understranding of their superstructures may offer inspiring guidance for rational polymer design, preparation, and further exploration in optoelectronic field.

Photoalignment of Vertically Oriented Microphase Separated Lamellae in LC-LC Diblock Copolymer Thin Film.

The microphase separation and photoalignment behavior of a diblock copolymer consisting of two kinds of side chain liquid crystalline (LC) polymers are investigated. Here, the mesogens of photoresponsive azobenzene and non-photoresponsive cyanobiphenyl are introduced in the side chains. The azobenzene and cyanobiphenyl mesogens orient homeotropically and planarly, respectively, in a thin film state. The combination of these contrasting orienting properties leads to a formation of vertically oriented lamella in the microphase separation structure. Irradiation with linearly polarized light onto this polymer film induces a highly oriented microphase separation structure having regularly elongated stripe morphology with 30 nm periodicity. The nearly defect-free morphology of this LC-LC diblock copolymer after the photoalignment is a distinct feature when compared with those of coil (amorphous)-LC diblock copolymer films possessing the same azobenzene side chain.

Photoresponsive liquid crystalline polymer single-chain nanoparticles

Single-chain nanoparticles prepared from a side-chain liquid crystalline polymer bearing azobenzene moieties can be multifunctional.

Densely grafted liquid crystalline copper phthalocyanine side chain polymer: synthesis and characterization

Synthesis and characterization of a liquid crystalline polymer with pendant copper phthalocyanine side chains (PCuPc).

Self-assembled helical columnar superstructures with selective homochirality

Helical columnar polymeric complexes with selective homochirality have been achieved from side-chain discotic liquid crystalline polymers doped with chiral acceptors.

Self-organization behaviours of hemiphasmidic side-chain liquid-crystalline polymers with different spacer lengths

The influence of flexible spacers on unusual self-organization behaviours of side-chain liquid-crystalline polymers containing biphenyl hemiphasmidic mesogens.

Influence of main chain on the phase behaviors of side‐chain liquid‐crystalline polymers with triphenylene mesogens of long alkyl tail substituents

ABSTRACTA series of side‐chain liquid‐crystalline polymers (SCLCPs) containing triphenylene mesogen, in which the long alkyl tail Tp connected directly with main chain, were synthesized successfully. The chemical structures of the monomers were confirmed by 1H NMR and mass spectrometry. The phase behaviors of polymers were investigated by a combination of techniques, including DSC, POM, 1D/2D WAXD, and SAXS. The experimental results suggested that the type of main chain played an important role in the LC phase structures of these polymers. Because of the steric effects of side chains and the coupling effects between the Tp moieties and the main chains, all the polymers exhibited columnar phase. However, the SCLCPs with poly(vinyl benzene methyl ether) or polynorbornene backbone displayed hexagonal columnar phase, while those with polyacrylate or polymethacrylate backbone presented columnar nematic phase, and the one with poly(vinyl benzoate) main chain showed rectangular columnar phase. Moreover, the clearing temperatures (Ti) changed with change in main chain. Especially, the Ti of the SCLCP with polymethacrylate backbone was above 300 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 754–766

Unimodal Nematic Liquid Crystalline Random Copolymers Designed for Accepting Chiral Dopants

Abstract The miscibility of chiral molecules to unimodal side-chain nematic liquid crystalline (LC) polymers was studied to generate chiral nematic phases. Chiral dopants, a phenyl benzoate derivative S-811 and an isosorbide dibenzoate derivative ISO-(6OBA)2 were miscible to the nematic LC polymer PMA(4OPB) tethering phenyl benzoate moieties as side-chain mesogens by preparing mixtures in solutions rather than directly melting the powders together. Nematic LC random copolymers containing non-LC side chains were designed to promote the interaction between mesogens and chiral molecules. The introduction of hexyl chains as side chains randomly into nematic LC polymers improved the miscibility of chiral molecules of an isosorbide dibenzoate derivative with hexyl tails. The hexyl chains of the polymer provided spaces for the chiral molecules and caused alkyl–alkyl interactions. We demonstrated that the randomly introduced hexyl chains promoted the interaction of chiral molecules with LC mesogens to generate chiral nematic phases.

Influence of alkyl tail length on self-organisation of side-chain liquid crystalline polymers with biphenyl hemiphasmidic mesogens

ABSTRACTA new and simple series of side-chain liquid crystalline polymethacrylates containing biphenyl hemiphasmidic mesogens based on 4-[(3,4,5-trialkan)-1-carbonylbenzoate]biphenyl (denoted as PTmBMA, m = 6, 8, 10, 12, 14, 16, 18, m refers to the carbon number of alkoxy tails) groups was designed and successfully synthesised via free radical polymerisation. The phase structures and transitions of the polymers were investigated by the combination of techniques including differential scanning calorimetry, polarizing microscope, one-dimensional/two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental results revealed that the liquid crystalline phase structures and behaviours of the polymers were found to be strongly dependent on the alkyl tail length (m). When m = 6, the PTmBMA formed a stable smectic phase above Tg. When m = 8, 10, 12, 14, 16, 18, the sample presented a hexagonal columnar mesophase (Φh), suggesting that the alkyl length has played an important role in the phase behaviours of hemiphasmidic side-chain liquid crystalline polymers.