Side-chain Liquid Crystalline Research Articles

Phase Behaviors and Photoresponsive Thin Films of Syndiotactic Side-Chain Liquid Crystalline Polymers with High Densely Substituted Azobenzene Mesogens.

Azobenzene-containing polymers (azopolymers) are a kind of fascinating stimuli-responsive materials with broad and versatile applications. In this work, a series of syndiotactic C1 type azopolymers of Pm-Azo-Cn with side-chain azobenzene mesogens of varied length alkoxy tails (n = 1, 4, 8, 10) and different length alkyl spacers (m = 6, 10) have been prepared via Rh-catalyzed carbene polymerization. The thermal properties and ordered assembly structures of thus synthesized side chain liquid crystalline polymers (SCLCPs) have been systematically investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM) and variable-temperature small/wide-angle X-ray scattering (SAXS/WAXS) analyses. P10-Azo-C1 and P10-Azo-C4 with shorter alkoxy tails exhibited hierarchical structures SmB/Colob and transformed into SmA/Colob at a higher temperature, while P10-Azo-C8 and P10-Azo-C10 with longer alkoxy tails only displayed side group dominated layered SmB phase and transformed into SmA phase at higher temperatures. For P6-Azo-C4 with a shorter spacer only showed a less ordered SmA phase owing to interference by partly coupling between the side chain azobenzene mesogens and the helical backbone. More importantly, the series high densely substituted syndiotactic C1 azopolymer thin films, exhibited evidently and smoothly reversible photoresponsive properties, which demonstrated promising photoresponsive device applications.

Studies of thermoluminescence properties of liquid crystalline N-phenyl substituted phenyl polysiloxane hydroxamic acids.

The investigation of thermoluminescence (TL) glow curves in liquid crystalline side chain N-phenyl-substituted phenyl polysiloxane hydroxamic acids (PHAs) has yielded significant insights. These polymers demonstrated TL behavior when exposed to β-radiation between 0 and 220°C, indicating inherent luminescent properties when irradiated. Notably, a dose-dependent relationship was observed in reported derivatized polymers; this study elucidates the diverse TL characteristics exhibited by various liquid crystalline side chain N-phenyl-substituted phenyl PHAs when exposed to β-radiation. Understanding these dose-dependent and dose-independent behaviors enhances the knowledge of their luminescent properties and potential applications in radiation detection.

Synthesis and Characterization of Side-Chain Liquid-Crystalline Block Copolymers Containing Cyano-Terminated Phenyl Benzoate Moieties

Block copolymers, known for their capacity to undergo microphase separation, spontaneously yield various periodic nanostructures. These precisely controlled nanostructures have attracted considerable interest due to their potential applications in microfabrication templates, conducting films, filter membranes, and other areas. However, it is crucial to acknowledge that microphase-separated structures typically exhibit random alignment, making alignment control a pivotal factor in functional material development. To address this challenge, researchers have explored the use of block copolymers containing liquid-crystalline (LC) polymers, which offer a promising technique for alignment control. The molecular structure and LC behavior of these polymers significantly impact the morphology and alignment of microphase-separated structures. In this study, we synthesized LC diblock copolymers with cyano-terminated phenyl benzoate moieties and evaluated the microphase-separated structures and molecular alignment behaviors. The LC diblock copolymers with a narrow molecular weight distribution were synthesized by atom transfer radical polymerization. Small angle X-ray scattering measurements revealed that the block copolymers exhibit smectic LC phases and form cylinder structures with a lattice period of about 18 nm by microphase separation. The examination of block copolymer films using polarized optical microscopy and polarized UV-visible absorption spectroscopy corroborated that the LC moieties were uniaxially aligned along the alignment treatment direction.

Design and Investigation of a Side-Chain Liquid Crystalline Polysiloxane with a Ntb-Phase-Forming Side Chain

A new mesogenic non-symmetric dimeric monomer with a terminal olefin function, forming a twist bend nematic (Ntb) as well as a nematic (N) phase, was synthesized, using an enhanced synthetic methodology, which avoids isomerization of the terminal double bond in the preparation of the dimer. This monomer was attached to a pentamethyldisiloxane group, resulting in the SmA LC phase behavior of the ensuing material. Linking the monomer to a siloxane main chain resulted in nematic phase behavior. Detailed studies with the Ntb phase forming dimer DTC5C7 show full miscibility of the dimer and the new LC polymer in the LC state, suggesting that the side-chain LC polymer forms a Ntb phase as the low-temperature nematic phase. Copolymerizing the monomer with a cyanobiphenyl-based monomer allows us to tune the glass transition and phase behavior further.

Synthesis and characterization of dendronized side chain liquid crystalline Poly(2-oxazoline)s towards biomimetic ion channels

The polymerization of dendronized monomers is an attractive option to synthesize liquid crystalline columnar polymers with side chain dendrons. Following this approach, we report for the first time in the present study the synthesis of a family of side chain liquid crystalline (SCLC) poly(2-oxazoline)s, poly(2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-2-oxazoline) (PTOx) from its oxazoline monomer precursor, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole) (TAPOx), by cationic ring-opening polymerization (CROP). The optimisation of the reaction parameters (temperature, type of initiator, terminating agent, solvent and monomer concentration), combined with the nature of the CROP allowed us to obtain high molecular weight SCLC poly(2-oxazoline)s. NMR investigations were consistent with the targeted molecular weights of the synthesized PTOx and the living nature of TAPOx polymerization. Regarding the mesomorphic characterization, all synthesized acyl-substituted poly(ethyleneimine)s exhibited liquid crystalline mesophases in a broad temperature range. XRD studies demonstrated that these dendronized poly(2-oxazoline)s self-assemble into columnar structures. Mesomorphic and thermal properties suggest that these family of poly(2-oxazoline)s could be excellent candidates to build up membranes for proton transport applications.

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.

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.

Tunable Thin Film Periodicities by Controlling the Orientation of Cylindrical Domains in Side Chain Liquid Crystalline Block Copolymers

A facile approach to block copolymer (BCP) domain orientation control in thin films has been demonstrated by employing a BCP with liquid crystalline semifluorinated side chains by tuning the composition of the copolymers of the bottom surface layer (BSL). 1H,1H,2H,2H-Perfluorodecanethiol was attached to a precursor polymer, polystyrene-block-poly(glycidyl methacrylate) (PS-b-PGMA), to obtain a novel BCP with a C8F17-containing liquid crystal (LC) side chain (PS-b-P8FMA). Anisotropic hexagonally packed cylinder domains in a bulk state were first characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The observed morphology transition of BCPs with different fluorinated side chain lengths of –CF3, –C4F9, and –C6F13 suggested the decisive effects of LC side chain ordering on the anisotropic nanostructures. In the thin film study, poly(methyl methacrylate-random-2,2,2-trifluoroethyl methacrylate-random-methacrylic acid) (PMMA-ran-PTFEMA-ran-PMAA) solution was used as BSLs for tuning the desired periodicities. The surface free energy (SFE) of BSL was simply tailored by changing the composition of comonomers. In atomic force microscopy (AFM) characterization, long-range ordered perpendicularly oriented BCP domains in a hexagonally packed array or parallel oriented BCP domains as striation patterns were easily fabricated on non-preferential or preferential BSL, respectively. The study presents a novel approach to tunable thin film periodicities without changing or modifying BCPs, which is desired in next-generation BCP lithography.

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.

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.

Liquid crystalline oligomers with a central core unit containing urethane groups

ABSTRACT Here, we show a generic approach to synthesis of oligomers which include modelling LC main chain polymers, LC side chain polymers or LC dendrimers. Four new families of LC oligomers derived from 1,6-hexamethylene diisocyanate and their di- or trimers (uretdione, biuret or isocyanurate) and ω-hydroxyalkylated cyanobiphenyls were prepared. Their mesomorphic and optical properties were investigated by differential scanning calorimetry and polarised optical microscopy. Mesomorphic properties were crucially impacted by the structure of the central core spacer (urethane, uretdione, biuret or isocyanurate). Stabilisation of the LC state of synthesised oligomers was attributed to the H-bonding interactions confirmed by FTIR spectra.

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.

Unconventional Approaches to Prepare Triazine-Based Liquid Crystal Dendrimers.

Most triazine-based liquid crystalline (LC) dendrimers reported thus far are the main-chain LC macromolecules with long flexible chains at their periphery and attached to internal rigid or semi-rigid frameworks. Their formation of mesogenic phases often depends on the intermolecular face-to-face π–π interactions between dendritic molecules, which are unusual. Their mesogenic phases can also be formed by incorporation of mesogenic units to the dendritic skeletons through long flexible chains, as most side-chain LC dendrimers, in which the peripheral mesogenic units generally play the important roles. For main-chain triazine-based dendrimers, their morphology is maintained by restricted freedom of rigid or semi-rigid connecting units, and their formations of LC phases are therefore not straightforward to be controlled. In this review, we thus describe modulating of the intermolecular face-to-face π–π interactions between the triazine-based dendritic molecules, with the aim of forming LC phases through molecular design.

Photoresponsive thin films of well-synthesized azobenzene side-chain liquid crystalline polynorbornenes as command surface for patterned graphic writing

Azobenzene-containing polymers (azopolymers) are a kind of intensively explored fascinating photoresponsive materials, liquid crystalline (LC) azopolymers with excellent film-forming, ordered structure and self-repairing capability are endowed with enhanced photoisomerization and photoalignment characteristics capable of developing into photo-modulated smart surfaces. Here in this work, two azobenzene side-chain LC polynorbornenes of PNB-Azo-n with different DP of n = 50 and 100 have been well synthesized through ring-opening metathesis polymerization (ROMP). The polynorbornene backbone of less flexibility with larger spacing between adjacent azobenzene side groups endows stronger inhibition for H-aggregation and better photoresponsiveness. The high-DP azopolynorbornene of PNB-Azo-100 thin films well behave as command surface for the upper layer nematic LC molecules thanks to their better performance in photoisomerization and photoalignment, together with their good compatibility and dissolution-resistance to the nematic LC mixture of E7. Selectively optically readable LC graphic writings at normal size through various photomasks have been demonstrated, and higher grid resolution up to sub-ten micrometer with a digital micromirror device (DMD) based dynamic photopatterning system has been achieved. Therefore, such kind of LC azopolynorbornenes demonstrate promising applications in LC photoalignment system and photoresponsive devices for potential anti-forgery document security and smart card technology.

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.

The Role of Liquid Crystalline Side Chains for Long-range Ordering in the Block Copolymer Thin Films

The Role of Liquid Crystalline Side Chains for Long-range Ordering in the Block Copolymer Thin Films

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...

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.

Effect of grafting density on the self-assembly of side-chain discotic liquid crystalline polymers with triphenylene discogens.

The self-assembly of triphenylene (TP)-based side-chain discotic liquid crystalline polymers (SDLCPs) with different grafting densities was investigated by using the dissipative particle dynamics (DPD) method. We explored the coupling effect between the main chain and the side-chain TP discogens with various length alkyl tails, and how the rigidity of the main chain, grafting density and spacer lengths affect the self-assembled morphologies of SDLCPs. By changing the above factors, we have obtained nine phases. It is deduced that a moderate grafting density, a polymer backbone with sufficient length and alkyl tails with medium length ensure SDLCPs form ordered columnar mesophases. It is worth noting that double columnar phases (Colne-Col and Colh-Col) were obtained with high grafting densities and sufficiently long backbones. All these results provide an effective basis and helpful guidance for the in-depth research of such kinds of fascinating organic semiconducting materials, SDLCPs, from the perspective of grafting density.