Polymer Network Films Research Articles

Large-area preparation of rainbow cholesteric liquid crystal polymer network films using a photoisomerizable chiral dopant

ABSTRACT Since the cholesteric liquid crystal polymer network (CLCN) films with a structural colour have been applied for decoration, those with colourful patterns become more attractive. They have been successfully prepared using photochromic cholesteric liquid crystals with the addition of photoisomerizable chiral dopants. Herein, two isosorbide derivatives with benzoate and cinnamate groups were synthesised using isomannide through chirality inversion and without using protecting groups. CLCN films were prepared using these two isomers as the chiral dopants. The structural colour of the films can be tuned by the photoisomerisation of the chiral dopants. Colourful patterns were also prepared using photomasks, which were suitably applied for decoration and anti-counterfeiting. Although the isomer with a higher melting point tended to induce the crystallisation of the CLC mixtures, the CLC mixtures prepared using the isomer with a lower melting point were stable at room temperature. Rainbow CLCN films were prepared using photomasks on a coating line.

Polymer Network Film with Double Reflection Bands Prepared Using a Thermochromic Cholesteric Liquid Crystal Mixture.

Cholesteric liquid crystal polymer network (CLCN) films with a single reflection band have found applications for decoration and anticounterfeiting. The CLCN films with double reflection bands were more suitable for these applications. Herein, they were prepared by using thermochromic cholesteric liquid crystals (CLCs) through a two-step photopolymerization approach. At the first step, due to oxygen inhibition, the CLC monomers near the substrate surface were polymerized at a certain temperature. At the second step, those near the air were polymerized at another temperature. The wavelengths of these two reflection bands of the CLCN film were dominated by the two polymerization temperatures. Based on this approach, patterns with composite colors were prepared, which were suitably applied for decoration. Moreover, a double-layered CLCN film with a broad reflection band was prepared that could potentially be applied for displays.

Color-tunable circularly polarized luminescence from liquid crystalline polymer networks

Chiroptical materials with circularly polarized luminescence (CPL) activities have attracted increasing interest because of their promising applications in optoelectronics, biosensing and imaging. Nevertheless, the construction of CPL-active materials with large luminescence dissymmetry (glum) factors and high emission efficiency is still challenging. Herein, a series of liquid crystalline polymer network films have been prepared by photopolymerization of cholesteric liquid-crystalline mixtures doped with aggregation-induced emission-active luminogens, TPE-TA and BDABFN. Through adjustment of the mass ratio of the two luminogens, the resultant films exhibit multicolour CPL from blue to red to white with absolute glum values up to 0.71 and fluorescence quantum yields up to 44 %. This work provides a strategy for fabricating polymeric film materials with color-tunable CPL properties and high fluorescence efficiency.

A cinnamate liquid crystal for rapid optical recording

ABSTRACT Photorecording materials have been applied for information recording. Herein, a cinnamate liquid crystal with an enantiotropic nematic phase was synthesised, which can be isomerised and polymerised under the irradiation of the 365-nm UV light. Cholesteric liquid crystal polymer network (CLCN) films were prepared using the mixtures of it, LC242, a chiral dopant and a photoinitiator. The CLCN films possess a slight gradient helical pitch which increases from the bottom to the top of the films. The formation of this structure should be driven by the photoisomerisation of the cinnamate. Under the irradiation of 365-nm UV light with a low intensity, the CLC mixtures show a photochromic behaviour which is proposed to be driven by the formation of oligomers. Based on this, the CLC mixtures can be applied for optical recording.

Handedness inversion of the Bragg reflection light of cholesteric liquid crystal polymer network film using a half-wave plate

Colourful cholesteric liquid crystal polymer network (CLCN) film can selectively reflect circularly polarized light whose handedness is consistent with that of the CLCN film. The CLCN patterns have been applied...

Structural coloured epoxy resin patterns prepared using thermochromic epoxy liquid crystal mixtures

Chiral epoxy liquid crystals were synthesized, which could be applied for the preparation of colourful cholesteric liquid crystal polymer network patterns. These patterns were suitably applied for decoration and anti-counterfeiting.

Upconversion circularly polarized luminescence of cholesteric liquid crystal polymer networks with NaYF4:Yb,Tm UCNPs.

Upconversion circularly polarized luminescence (UC-CPL) exhibits promising potential for application for anti-counterfeiting and displays. Upconversion nanoparticles (UCNPs), NaYF4:Yb,Tm, with uniform morphology and high crystallinity, were prepared via a simple solvothermal method. These UCNPs were embedded into cholesteric liquid crystal polymer network (CLCN) films. The UC-CPL performance of these films was investigated using left- and right-handed circular polarizers. After calibration, the |gcallum| values (up to 0.33) were obtained for the free-standing CLCN-UCNPs films, while a |gcallum| value of 0.43 was achieved for the CLCN-UCNPs-coated PET film. Moreover, a combined system comprising a PMMA-UCNPs layer and a CLCN layer yielded an ultra-large |gcallum| value of up to 1.73. Flexible and colourful patterned CLCN films were fabricated using photomasks, offering potential applications in anti-counterfeiting. This study not only successfully prepared UC-CPL-active materials based on CLCNs and UCNPs, but also demonstrated the chiral filtering effect of CLCN films in upconversion luminescent materials.

Efficient multicolour and white circularly polarized luminescence from liquid crystalline polymer networks.

Twelve liquid crystalline polymer network films were fabricated through photopolymerization of cholesteric liquid-crystalline mixtures containing two aggregation-induced emissive-active luminogens. The films exhibit multicolour and white circularly polarized luminescence with dissymmetry factors up to 0.85 and fluorescence quantum yields up to 90%.

Real-time visual humidity response films of interpenetrating polymer network based on cholesteric liquid crystal and poly (acrylic acid)

ABSTRACT Humidity sensors play a critical role in diverse fields such as agricultural production, medical equipment, and weather forecasting. However, the majority of existing humidity sensors rely on batteries or are relatively costly to construct. In this study, a simple, efficient, and battery-free visual humidity sensor was developed by combining cholesteric liquid crystal (CLC) with acrylic acid (AA) and subsequently curing it to form an interpenetrating polymer network (IPN) film. The IPN film changes colour with relative humidity (RH). Moreover, it has been confirmed that the film exhibits excellent repeatability, and its performance remains relatively unaffected by temperature fluctuations. Additionally, the relationship between film thickness and response time is explored in this research. Through orthogonal experiments involving various proportions of CLC, the study also scrutinises the influence of each component on the humidity response performance of the IPN films. During the transition from 40% RH to 90% RH, IPN film sample 3 experienced a remarkable redshift of 123.05 nm in the reflected wavelength. As for sample 9, its humidity response demonstrated an outstanding linearity of 0.9986. Consequently, the experimental outcomes provide strong evidence that this IPN film exhibits superior humidity response capabilities and holds considerable promise for practical applications.

Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback.

Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.

Development of thin film coatings with polypyrrole (ppy) by physical plasma deposition technique (PAPVD) for electrochemical capacitor

In this study, new polypyrrole films (ppy) were synthesized using a physical plasma deposition (PAPVD) system; where the equipment design and methodology for plasma-assisted pyrrole polymerization were improvement. The morphology, functional groups, and thermal stability of the polymer network films were characterized by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) techniques, respectively. The electrochemical properties of the films as capacitor were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The results observed by SEM showed that the ppy 100W-1 and ppy 100W-2 films present uniformity in their structure. The analyses of TGA and DSC confirmed the improvement in stability; meanwhile for 100W-1 film, the presence of ppy bonds was corroborated by XPS. Plasma-activated ppy 100W-1 film exhibited higher capacitance and minor Rct resistance than that obtained for ppy 100W-2 film. The specific capacitances values of ppy 100W-1 and ppy 100w-2 films are 196 and 150 F/g in 1 M KCl. After charging and discharging tests of 1000 cycles at 5 mA cm−2 current density of ppy 100W-1 film retains 89% of its initial capacitance. Therefore, ppy 100W-1 film showed to be a promising material for use as an electrochemical capacitor.

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.

Mesoporous ionic liquid functionalized nanozeolite: Synthesis and high efficient material to improving pseudocapacitance performance of conductive polymer

Supercapacitors are emerging as a competitive candidate for electrochemical energy storage owing to their greater power outputs and longer cycle life than rechargeable batteries. In this work, a chloropropyl grafted zeolite-NaY modified with imidazolium chloride ionic liquid (Im-Cl IL@ZY) has been successfully synthesized by a chemical method. Notably, the imidazolium chloride ionic liquid enhances the electrical contact between zeolite network and conductive polymer film (poly ortho aminophenol) because of its high conductivity and good compatibility with different substances. The synergistic effect of the most efficient composite endows the hybrid electrode with a high specific capacitance of 665 F/g F g−1 at 1 A g−1 and reliable cycling stability of 88 % capacitance retention after 8000 cycles. Moreover, a symmetric supercapacitor based on the composite electrodes achieves a high energy density of 36.7 W h kg−1 at a power density of 485 W kg−1. Results highlight that POAP/Im-Cl IL@ZY composites are promising materials for energy storage devices with long cycling stability.

Enhancing the CO2-H2S corrosion resistance of oil well cement with a modified epoxy resin

The primary function of cement ring is to support and hang the casing, seal formation fluids and prevent interlayer channeling. However, in high-acid oil and gas fields, the cement ring is susceptible to corrosion by acidic media such as CO2 and H2S, which seriously shortens the production life of oil and gas wells and causes substantial economic losses. Therefore, it is very important to study the anti-corrosion performance of cement ring. Given the excellent bonding performance, high mechanical properties, and good corrosion resistance of epoxy resin, in this study, water-based modified epoxy resin was used as the anti-corrosion material to improve the anti-corrosion performance of oil well cement. The corrosion resistance of cement stone with modified epoxy resin was evaluated in acidic media in gas phase and liquid phase under simulated formation environment, and the corrosion resistance mechanism was analyzed. Studies have shown that the corrosion resistance of cement stone added with modified epoxy resin was significantly improved. After 30 days of corrosion in liquid and gas phase acidic medium, the strength loss rates were 9.8 % and 1.2 %, and the corrosion depths were 3.1 mm and 10.6 mm, respectively. Compared with cement stone without modified epoxy resin, the strength loss rates were as high as 32.1 % and 17.6 %, and the corrosion depths were 16.1 mm and 36.6 mm under the same corrosion conditions. SEM analysis shows that modified epoxy resin improves the corrosion resistance of cement stone mainly by filling pores to improve the compactness of cement stone structure and forming three-dimensional network polymer film to isolate acidic medium.

Programmable Liquid Crystal Defect Arrays via Electric Field Modulation for Mechanically Functional Liquid Crystal Networks.

The arrangement of mesogenic units determines mechanical response of the liquid crystal polymer network (LCN) film to heat. Here, we show an interesting approach to programming three-dimensional patterns of the LCN films with periodic topological defects generated by applying an electric field. The mechanical properties of three representative patterned LCN films were investigated in terms of the arrangement of mesogenic units through tensile testing. Remarkably, it was determined that LCN films showed enhanced toughness and ductility as defects increased in a given area, which is related to the elastic modulus mismatch that mitigates crack propagation. Our platform can also be used to modulate the frictional force of the patterned LCN films by varying the temperature, which can provide insight into the multiplex mechanical properties of LCN films.

Security use of bilayer dichroic films made of liquid crystal polymer networks

ABSTRACT We report on bilayer dichroic dye-doped liquid crystal (BDLC) films for patternable color codes, which can be used in anti-counterfeiting applications such as security codes and, unlike the conventional single-layer LC color films, show unique color changes depending on the direction of the polarization of the incident light that passes through them. This is a facile way to enhance the security level of security codes. BDLC films are fabricated by laminating two single-layer LC polymer network films with crossed optical axes. We believe that BDLC films can be used as a new platform for a security-enhanced anti-counterfeiting code that can replace complex chiral materials or expensive plasmonic particles.

Photosynthesis of polymer networks with controlled properties by dimerization of cinnamoyl groups

AbstractPhotosensitive monomers/polymers/copolymers containing a variable amount of cinnamoyl (Ci) groups ranging from 3 up to 480 per molecule were synthesized. These precursors were photocrosslinked by irradiation with UV light of wavelength 320–380 nm via the photodimerization of the Ci units. The evolution of conversion, gel fraction, modulus and Tg during irradiation was followed. Two types of photosensitive systems were studied: (i) a blend of photosensitive precursors of different functionality fCi and (ii) copolymers with a different content of Ci units and Tg. The control of the precursors' structure and composition as well as photocuring time period make it possible to finely tune the properties of the formed polymer network films. The prepared photocrosslinked networks show a very broad range of thermomechanical properties with Tg from −25 °C up to 135 °C and moduli over a range of three orders of magnitude. © 2021 Society of Chemical Industry

Development of leftover rice/gelatin interpenetrating polymer network films for food packaging

Abstract Waste biomass can be used as a raw material for food packaging. Different concentrations of gelatin (GEL) were introduced into the leftover rice (LR) system to form an interpenetrating polymer network (IPN) for improving the properties of the films. The structure and morphology of films were evaluated by Fourier transform infrared, scanning electron microscopy, and atomic force microscopy, which showed good compatibility between LR and GEL. The moisture content and oil absorption rate of IPN films were down by 105% and 182%, respectively, which showed better water and oil resistance than the LR film. In addition, increasing GEL concentration led to enhancement in the tensile strength of films from 2.42 to 11.40 MPa. The water contact angle value of the IPN films (117.53°) increased by 147% than the LR film (47.56°). The low haze of IPN films was obtained with the increment of the mutual entanglement of LR and GEL. The 30–50% GEL addition improved the water vapor barrier and thermal stability properties of the IPN films. This study highlights that LR as waste biomass can have a practical application in food packaging.

Ligand-Controlled Electrochromic Diversification with Multilayer Coated Metallosupramolecular Polymer Assemblies.

Designing surface-confined molecular systems capable of expressing changes in functional properties as a result of slight variations in chemical structure under the influence of an external stimulus is of contemporary interest. In this context, we have designed three tetraterpyridine ligands with variations in their core architecture (phenyl vs tetraphenylethynyl vs bithiophene) to create spray-coated electrochromic assemblies of iron(II)-based metallosupramolecular polymer network films on transparent conducting oxide substrates. These assemblies exhibited molecular permeability and spectroelectrochemical properties that are in turn dictated by the ligand structure. Electrochromic films with high coloration efficiencies (up to 1050 cm2/C) and superior optical contrast (up to 76%) with a concomitant color-to-color redox transition were readily achieved. These functional switching elements were integrated into sandwich-type electrochromic cells (CE up to 641 cm2/C) that exhibited high contrast ratios of up to 56%, with attractive ON-OFF ratios, fast switching kinetics, and high operational stability. Every measurable spectroelectrochemical property of the films and devices is an associated function of the ligand structure that coordinates the same metal ion to different extents. While exhibiting a ligand-structure induced differential metal coordination leading to porosity and spectroelectrochemical diversification, these assemblies allow the creation of electrochromic patterns and images by a simple spray-coating technique.

Development of sustainable and antimicrobial film based on polybenzoxazine and cellulose

A new class of bio based polymer blends have been prepared from a modified chitosan based benzoxazine precursor (E-ch) and amino cellulose (AC). AC was derived from cellulose with excellent film-forming, biocompatibility and biodegradability property. E-ch was synthesized from eugenol, modified chitosan and paraformaldehyde. The chemical structure was confirmed by FT-IR and 1H NMR analyses. Bio films were prepared by mixing E-ch and AC with diluted acetic acid, in different ratios. These films were further cross-linked by applying heat, via ring-opening polymerization of benzoxazine without any curing agent. FT-IR and DSC were used to study the effects of AC on E-ch to form cross-linked network polymer films [poly(E-ch)/AC]. Hydrogen bonding interactions were found to exist between poly(E-ch) and AC. These kinds of interactions considerably improve the mechanical and thermal properties and char yield of the polymer films. Additionally, these biofilms; poly(E-ch) and poly(E-ch)/AC have been examined for bio-activity with S. aureus. It is confirmed that these bio-films are effective in inhibiting bio-film related infection. In a similar way, both the bio-films act against C. albicans and thus avoid the formation of mycological infection. These results expose that poly(E-ch) and AC bio-films are capable to act as anti-microbial and anti-fungal agents.