Polymer Light Research Articles

Thiophene substituted phenothiazine polymers: Design, synthesis and characterization

In this paper, the polymers containing phenothiazine were synthesized via oxidative polymerization reaction by FeCl3 as oxidant. These polymers contain ether unit, aliphatic chain and aromatic groups as bridges in their structures. The effects of the groups on the optical, thermal, morphological properties of the polymers were investigated. The physical and chemical properties of the monomers and the polymers were identified by FT-IR, NMR, UV–Vis, thermogravimetry (TG), cyclic voltammetry (CV), fluorescence analysis. According to the fluorescence analyses, polymer containing aliphatic ether bridge emitted yellow colour based on the turning of excitation wavelength. The yellow solution of polymer containing aliphatic ether bridge turned into turquoise when excited with the wavelength of 365 nm. Thermal analyses demonstrated that polymer containing phenyl bridge compound had 38% residue amount. Due to fluorescent and thermal properties, these polymers could be used in various applications such as spectrofluorometric ion sensor and polymeric light emitting diodes (PLEDs) with yellow and turquoise emissions.

To inhibit coffee ring effect in inkjet printing of light-emitting polymer films by decreasing capillary force

Polymer thin film with uniform thickness and flat surface profile is the key point for polymer light emitting diodes (PLEDs) by inkjet printing. However, the coffee ring effect is usually observed due to the mismatch between the evaporation of the solvent and the decrease of solution volume, which promotes the formation of radial flow from the interior of the drop to the edge. In this paper, coffee ring effects of inkjet printed poly(spirobifluorene) films were proposed to be restrained by decreasing capillary force by adding co-solvent with high boiling point and high viscosity to the main solvent. The low evaporation rate of the co-solvent can reduce the driving force of the radial flow; meanwhile the high viscosity of the co-solvent can increase the resistance of the radial flow. Thus, polymer films with improve uniformity can be obtained due to the suppression of the radial flow. The device performance was greatly improved under the condition of proper film thickness and film uniformity and the maximum luminous efficiency of devices with inkjet printed poly(spirobifluorene) can reach 80% of the spin-coated devices.

Double network shape memory hydrogels activated by near-infrared with high mechanical toughness, nontoxicity, and 3D printability

In this work, near-infrared (NIR)-responsive double network shape memory hydrogels were formed by chemically cross-linking Pluronic F127 diacrylate macromer (F127DA) and physical blending of poly(lactide-co-glycolide) (PLGA) with graphene oxide (GO, an energy convertor to convert NIR irradiation to thermal energy). The hydrogels were manufactured with 3D-printing technology using ultraviolet light polymerization. The morphologies and crystalline structure of the hydrogels were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The NIR and thermal activated shape memory properties, mechanical toughness, and cytotoxicity were investigated. The shape memory properties were improved by incorporating GO into the hydrogels and the mechanical properties were enhanced by the addition of PLGA, which served as a second network. The cytotoxicity was assessed by the CCK-8 assay, which revealed no cytotoxicity. The nontoxicity, high mechanical toughness (3.45 MPa in the swollen state), and biosafety at the shape recovery temperature (36 ± 1 °C), which was achieved by NIR stimuli, indicates that shape memory hydrogels can be used in biomedical materials safely. The practical potential of the F127DA/PLGA/GO hydrogels was further revealed by their 3D-printing performance, their shape fixity ratio greater than 85%, and their shape recovery time under 300 s. Our results propose that F127DA/PLGA/GO hydrogels will be a promising material in biomedical applications as a drug carrier and an antibacterial scaffold.

Amphiphilic fluorinated block-copolymer coating for the preparation of hydrophobic porous materials

A new approach to the preparation of hydrophobic porous polymers has been proposed. Three series of porous polymers which pores equally well-absorbed as water and organic liquids (benzene and iso-octane) were synthesized by visible light polymerization from compositions based on three different dimethacrylic esters with n-butanol. Three block copolymers based on N-vinylpyrrolidone and 2,2,3,3-tetrafluoropropyl methacrylate, differing in the length of the poly-(2,2,3,3-tetrafluoropropyl methacrylate) block, were synthesized for the purpose of hydrophobization of such porous polymers. A distinctive feature of synthesized block copolymers is that they are soluble only in methanol. It has been found that the treatment of porous polymers only with 2 wt.% of block copolymer methanol solution leads to a decrease water uptake by an order of magnitude, and the absorption of organic liquids does not change. In the course of the study it was possible to obtain a hydrophobic porous polymer sample that has water contact angle θ = 121° and a low value of the polar component of the surface Gibbs energy ( $$ {\gamma}_s^p=0.2 $$ mJ·m−2). The fundamental possibility of using such material for purification of organic liquids from water is shown.

Ultrafast Energy Transfer Followed by Electron Transfer in a Polymeric Nanoantenna-Based Light Harvesting System

A polymeric nanoantenna-based light harvesting system is prospective because of it captures more number of photons by a multichromophoric donor and subsequently transfers its energy to the acceptor. Here, we have designed an aqueous solution-based polymeric nanoantenna, where conjugated polymer nanoparticles (donor) are attached with Au nanoparticle-capped porphyrin (acceptor)-encapsulated bovine serum albumin protein for both energy transfer and electron transfer processes. Ultrafast fluorescence upconversion and transient absorption spectroscopic studies reveal that the ultrafast energy transfer occurs from the conjugated polymer nanoparticle to porphyrin in 130 fs, followed by the electron transfer from porphyrin to Au nanoparticles in 70 ps after photoexcitation. Furthermore, the antenna effect of this light harvesting system is found to be 79 at the donor to acceptor ratio of 16:1. Analysis reveals that this polymeric nanoantenna opens up a new avenue for designing a highly efficient aqueous solution...

Facile preparation of microscale hydrogel particles for high efficiency adsorption of bisphenol A from aqueous solution.

Hydrogel microparticles (HMPs) were synthesized via reverse emulsion/UV light polymerization and employed as adsorbents for removing bisphenol A (BPA) from aqueous solution. Results demonstrated the smooth surface of HMPs, with particle size ranging from 137 to 535μm. Functional groups, including -OH, C-O, C=O, and C-H, are all involved in BPA adsorption confirmed by FTIR. Effect of solution pH, contact time, and initial BPA concentration on adsorption process was examined. The adsorption capacity was found pH independent below pH8.0 and decreased when pH values greater than 8.0. The maximum adsorption capacity of the HMPs for BPA was 174.77mg/g. The adsorption process achieved an equilibrium state within 30min by the pseudo-second-order kinetic rather than the other kinetic models and was fitted well with the Freundlich linear isotherm model. Also, the obtained isotherms reflected the formation of S-type isotherm curve according to Giles's classification. The BPA loaded on the HMPs could be totally regenerated by methanol/dimethylsulfoxide and can be used for five cycles maintaining 100% of adsorption capacity. When the HMPs were applied for the treatment of spiked real surface water, excellent results were also achieved indicating the high efficiency and potential of the adsorbent.

Microwave-assisted synthesis of colloidal ZnO nanocrystals and their utilization in improving polymer light emitting diodes efficiency

Zinc oxide nanoparticles were synthesized via microwave-assisted reactions from a zinc acetate dihydrate. The reactions were performed in diethylene glycol (DEG) at 220 °C and 250 °C while using oleic acid as the surfactant. The ZnO precipitates obtained were washed with methanol and dried or kept as colloidal solutions redispersed in toluene. The size of the nanoparticles ranged from ca. 5 to 12 nm and they could be modified by the concentration of Zn precursor. Different morphologies due to the function of oleic acid concentration were observed. The resulting ZnO nanocolloids were mixed with the poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to obtain MEH-PPV/ZnO nanocomposites. The nanocomposite layers exhibited optoelectronic properties which were found to be beneficial for being applied as the active layer in the polymer light emitting diodes. The intensity of the electroluminescence of the prepared PLED devices was enhanced by one order of magnitude keeping all other parameters constant and powered as the same operation voltage. As additional step the effect of active layer thickness on optoelectronic performance of PLED devices was investigated as well.

Single mode waveguiding effect of ZnO nanorods to enhance the luminance of conjugated polymer based light emitting diodes

In the present work, a unique strategy to improve light emission from poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) based polymer light emitting diodes (PLEDs) has been reported. It was observed that integration of vertical ZnO nanorods (NRs) in the PLED structure drastically enhances the luminance (more than 20 times) as compared to that of basic MEH-PPV device. The analysis reveals that the waveguiding effect of NR structure is responsible for this phenominal enhancement. ZnO NRs possess large acceptance angle and are able to direct the collected light perpendicular to the ITO plane through single mode propagation. This rectifies the problem of undesired total internal reflection at ITO/glass and glass/air interfaces, which is the root cause of reduced light extraction from PLEDs.

Effect of (meth)acrylates on in situ visible light polymerization of dimethacrylamide

This study reports in situ visible light copolymerization of a synthesized dimethacrylamide with the selected (meth)acrylates. The effects of these selected comonomers with different functional groups on the polymerization rate, degree of conversion, gel time and compressive strength were investigated. The results showed that in situ copolymerization of the dimethacrylamide with the comonomers having an electron-withdrawing and/or acrylate group could significantly increase the polymerization rate, degree of conversion and compressive strength. Contrarily, an electron-donating group on either carbon–carbon double bond or ester linkage could slow down the polymerization. In comparison, its methacrylate counterpart, triethylene glycol dimethacrylate-based system did not show a clear pattern. The formed H-bonds between (meth)acrylamide and organic acid groups may be responsible for higher compressive strengths. Within the limitation of this study, it is concluded that in situ polymerization of dimethacrylamide under visible light can be accelerated by copolymerization with monomers having electron-withdrawing and/or acrylate groups and vice versa.

Does the Translucency of Novel Monolithic CAD/CAM Materials Affect Resin Cement Polymerization with Different Curing Modes?

The translucency of CAD/CAM blocks influences the polymerization efficiency of resin cement used underneath. The aim of this study is to evaluate the influence of the translucency parameters (TPs) of current monolithic CAD/CAM blocks on the microhardness of light-cured or dual-cured resin cement. 100 specimens were prepared from five types of CAD/CAM blocks (Mark II, Suprinity, Enamic, e.max, Ultimate), and their TP values were measured by spectrophotometry; 100 resin cement specimens (Duolink) were cured underneath five ceramic specimen groups by indirect LED light for 40 seconds with dual-cure (with catalyst) and light-cure (without catalyst) polymerization modes. Control group resin cement specimens (n = 20) were cured with both polymerization modes by direct LED light without any ceramic disc, making 120 resin cement specimens in total. The specimens were then stored in a dry environment for 24 hours before measurement of the polymerization depth with a digital micrometer. Vickers hardness measurements were performed at different resin cement sections. The results were statistically analyzed with 1-, 2-, and 3-way ANOVA, Student's t-test and Tukey's HSD test (α = 0.05). The highest TP values occurred for Suprinity and Ultimate, whereas the lowest TP value occurred for Enamic (p < 0.01). The depth of cure and Vickers hardness values changed proportionally with TP value. In all specimens, dual polymerization provided higher depth of cure and Vickers hardness values than those obtained using light polymerization (p < 0.01). In all specimens except Enamic, the hardness value differences between the sections were statistically insignificant (p > 0.05). In Enamic, the hardness values for both polymerization types decreased significantly in the deeper sections (p < 0.01). Lower depth of cure was observed as the amount of transmitted light decreased in the investigated materials. In clinical practice, light-cured resin cements may result in inadequate polymerization for ceramic materials with lower TP values. Zirconia-reinforced lithium silicate and nanoceramic resins may be reliable restorative materials for a restoration with both optimal esthetics and sufficient mechanical strength resulting from proper polymerization.

TiO2 nanorod arrays induced broad-band reflection in chiral nematic liquid crystals with photo-polymerization network

ABSTRACTA series of TiO2 nanorod arrays were obtained by hydrothermal reaction, then the morphologies were characterized and analysed. In the light polymerization condition, different morphologies of TiO2 nanorod arrays and chiral nematic liquid crystalline (N*-LCs) media were combined to prepare broad-band reflectors. By adjusting the length and interval size of the TiO2 nanorod arrays, the reflection spectra and the positions of the reflected spectrum and the reflected bandwidth can be controlled accordingly. As a result, the effect of polymerization temperatures and morphologies of TiO2 nanorod arrays on the broad-band reflection in the N*-LC composite system has been investigated. Potential applications of the composite were related to brightness enhancement films, bandwidth-controllable reflective polarizers and near-infrared light blocking films.

Growth of thiophene based oligomers using Stille and direct arylation methods for optoelectronic applications

Palladium catalyzed Stille coupling reactions are extensively used for the preparation of functionalised thiophene based polymers. In addition, polycondensation via direct C-H arylation produces alternating copolymers in moderate yields. In the present work, we report the synthesis and optoelectronic properties of thiophene based compounds having rigid cycloalkanone and a novel hexhydro-2H-indazole spacers in between. X-ray diffraction analysis shows the semi-crystalline nature of the synthesized materials with extensive side chain crystallinity. Band-gap energy of the synthesized materials has been obtained experimentally via optical and electrochemical methods and theoretically via computational studies. Open aperture Z-Scan results confirm the competence of these materials as optical limiters (NLO) while the photoluminescence emission characteristics and Schottky diode characteristics indicate their application prospects in Polymer Light Emitting Diodes (PLEDs). Polymers having hexhydro-2H-indazole spacers appear to be promising candidates for optoelectronic applications.

Electrical and optical numerical modeling of DP-PPV based polymer light emitting diode

Abstract In this paper, an in-depth study of the electrical and optical characteristics of Polymer Light Emitting Diodes ITO/PEDOT: PSS/DP-PPV derivatives/Al(Ca) is presented. Three polymer materials are considered; poly(2,3-diphenyl-5-(4-heptyloxy-4'-oxytrimethylenediphenyl)-phenylenevinylene) (P1), poly(2,3-diphenyl-5-[4-(4-pentylcyclohexyl)phenoxy]-propyl-p-phenylene vinylene) (P2) and poly(2,3-diphenyl-5-(2-(1, 4, 5-triphenyl-1H-2-imidazoloyl)-1-oxytrimethylene phenyl) phenylene vinylene) (P3). The J-V characteristics are investigated using a device model which includes the injection, transport, and recombination mechanisms. The electron and hole mobility of each material are fitted to experimental data. The charge balance factor CBF, the external quantum efficiency EQE, the Langevin recombination rates and the singlet exciton densities profiles are studied. The results are found to be in a good agreement with experimental data especially in the low current densities region, indicating that these PLEDs electrons mobility affects greatly the J-V characteristics compared with holes mobility, and that is because electrons band offset smaller than that of holes. The best performance is obtained with P1 device with a CBF value of almost unity and an EQE still low (4.7 %) but similar to other PPVs and MEH-PPVs based devices.

Colloidal cobalt-doped ZnO nanoparticles by microwave-assisted synthesis and their utilization in thin composite layers with MEH-PPV as an electroluminescent material for polymer light emitting diodes

Abstract CoxZn1-xO (x = 0.01, 0.05 and 0.1) nanoparticles were prepared by microwave-assisted polyol method from zinc acetate dihydrate and Co(II) acetylacetonate. The reactions were performed in diethylene glycol (DEG) at 250 °C with the use of oleic acid as a surfactant. Resulting nanoparticle (ca. 10 nm) precipitates were washed with methanol and dried or kept as colloidal solutions redispersed in toluene. Colloidal solutions were mixed with the Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to produce thin nanocomposite layers with specific optoelectronic properties. The electronic structure in terms of density of states (DOS) of MEH-PPV and MEH-PPV/nanocomposite layers was investigated by recently proposed energy resolved electrochemical impedance spectroscopy method. The MEH-PPV polymer and its nanocomposites with ZnO or CoxZn1-xO nanoparticles were used as thin active layers in polymer light emitting diodes (PLED). The nanocomposite layers exhibited optoelectronic properties which were found to be beneficial as the active layer in PLEDs, exhibiting an order of magnitude enhancement in electroluminescence intensity. A pronounced effect on the opening bias voltage of final devices with CoxZn1-xO nanoparticles was also observed.

Parametric analysis of thin multifunctional elastomeric optical sheets

Abstract Flexible optical sheets are thin large-area polymer light guide structures that can be used to create innovative passive light-harvesting and illumination systems. The optically transparent micro-patterned polymer sheet is designed to be draped over arbitrary surfaces or hung like a curtain. The light guidance sheet is fabricated by bonding two or more micro-patterned layers with different indices of optical refraction. By imprinting micro-optical elements on the constituent layers, it is possible to have portions of the optical sheet act as a light concentrator, near ‘lossless’ transmitter, or diffuser. However, the performance and efficiency of the flexible optical sheet depends on the overall curvature (κ) of the optical sheet and the relative orientation of incident light source. To illustrate this concept, the impact of key design parameters on the controlled guidance of light through a two-layer polydimethylsiloxane (PDMS) concentrator-transmitter-diffuser optical sheet is investigated using ray tracing simulation software. The analysis initially considers a flat (κ=0) PDMS optical sheet exposed to a collimated light source. The impact of sheet curvature (κ&gt;0) on both system efficiency and illumination uniformity is then briefly explored. Critical design guidelines for creating multifunctional monolithic optical sheets are also summarized.

Enhancement in fluorescence quantum yield of MEH-PPV:BT blends for polymer light emitting diode applications

We have investigated the effect of blending electron deficient heterocycle Benzothiadiazole (BT) on the photo-physical properties of conjugated polymer Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Quantum yield (QY) value has been found to increase from 37% for pure MEH-PPV to 45% for an optimum MEH-PPV:BT blend ratio of 1:3. This can be attributed to the efficient energy transfer from the wide bandgap BT (host) to the small bandgap MEH-PPV (guest). The FTIR spectrum of MEH-PPV:BT blended thin film indicates suppression of aromatic C-H out-of-plane and in-plane bending, suggesting planarization of the conjugated polymer chains and, hence, leading to increase in the conjugation length. The increase in conjugation length is also evident from the red-shifted PL spectra of MEH-PPV:BT blended films. Single layer MEH-PPV:BT device shows lower turn-on voltage than single layer MEH-PPV alone device. Further, the effect of electrical conductivity of PEDOT:PSS on the current-voltage characteristics is investigated in the PLED devices with MEH-PPV:BT blend as the active layer. PEDOT:PSS with higher conductivity as HIL reduces the turn on voltage from 4.5 V to 3.9 V and enhances the current density and optical output in the device.

P‐209: Late‐News Poster: Ordered and Coplanar Chain Conformation of Polyfluorenes by Adopting Solvent Vapor Treatment Process for Enhanced Color Purity in Polymer Light Emitting Diode

We investigated molecular chain conformation effect in polyfluorenes (PFO) according to film preparation conditions. By using solvent vapor annealing and introducing anisotropic alignment interface, the molecular conformation of the β phase could be effectively enhanced. The electroluminescence properties of the alterative current driven PLED with the β phase‐enhanced PFO layer exhibited improved color purity for blue, polarized light emission, and more reliable light‐emitting operation owing to the ordered and coplanar molecular chain conformation effects.

Synthesis of hydroxyl-terminated polybutadiene bearing pendant carboxyl groups by combination of anionic polymerization and blue light photocatalytic thiol-ene reaction and its pH-triggered self-assemble behavior

Polybutadiene with the simultaneous presence of hydroxyl end-groups and pendant carboxyl side groups was successfully synthesized by combination of living anionic polymerization and blue light photocatalytic thiol-ene “click” reaction. Firstly, hydroxyl-terminated polybutadiene (HTPB) with high content of 1,4-butadiene unit was synthesized by living anionic polymerization using hydroxy-protected initiator, and followed by de-protection. Then, double bonds in backbone of HTPB were modified into pendant carboxyl side groups by blue light photocatalytic thiol-ene “click” reaction using Ru(bpy)3Cl2 and p-toluidine as photoredox catalysts. The blue light photocatalytic thiol-ene reaction exhibit high-efficiency, and all the unsaturated bonds were modified after reacting for 5 h, in spite of that in-chain double bonds in 1,4-butadiene units are much less reactive than vinyl groups in 1,2-butadiene units. When all the double bonds were modified, the structure of resulting polymer can be deemed as carboxyl functionalized hydroxyl-terminated polyethylene. Furthermore, the solution properties of resulting polymer have been investigated by various technologies. The results showed carboxyl functionalized hydroxyl-terminated polyethylene experience a dissolution-assembly-aggregation transition process with pH value of solution decreased from 12.0 to 2.0. The mechanism of this pH-triggered phase transition behavior was supposed to depend on the ionization of carboxyl side groups at varying pH values.

Remotely Phototriggered, Transferrin-Targeted Polymeric Nanoparticles for the Treatment of Breast Cancer.

Triple-negative breast cancer (TNBC) has the worst prognosis among all subtypes of breast cancer. Currently, no targeted treatment has been approved for TNBC. The goal of this study was to design a remotely triggered, targeted therapy for TNBC using polymeric nanoparticles and light. Active targeting of TNBC was achieved by conjugating the nanoparticles to a peptide (hTf) that binds to the transferrin receptor, which is overexpressed in TNBC. Photodynamic therapy (PDT) was explored for TNBC treatment by remotely triggering benzoporphyrin derivative monoacid (BPD), a photosensitizer, using near-infrared light. In this study, we investigated the use of actively targeting polymeric nanoparticles for PDT against TNBC using in vitro imaging and cytotoxicity studies. Fluorescence imaging confirmed that the BPD-loaded nanoparticles showed greater fluorescence in TNBC cells compared to free BPD, but more importantly, actively targeted nanoparticles displayed stronger fluorescence compared to passively targeted nanoparticles. Moreover, fluorescence imaging following competition with empty targeted nanoparticles validated the specificity of the targeted nanoparticles for TNBC cells. The PDT killing results were in line with the fluorescence imaging results, where actively targeting nanoparticles exhibited the highest phototriggered cytotoxicity in TNBC cells, making them an attractive nanoplatform for TNBC treatment.

Highly efficient solution-processed inverted polymer light emitting diodes with uniformly coated poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) layers on a hydrophobic emission layer using a dilution method

Inverted polymer light emitting diodes (PLEDs), where solution-processed multi-layers were sandwiched between indium tin oxide and thermally evaporated aluminum electrodes, were fabricated and their characteristics were measured. In order to achieve high performance in the inverted PLEDs, there is a need for additional functional layers such as a hole transport layer and hole injection layer (HIL) on an emission layer (EML), but formation of the solution-processed layers on the hydrophobic EML have been rarely reported due to the extremely poor wetting property of a poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) solution, which is a widely used HIL. Non-wetting phenomena such as the formation of islands or radiation patterns in PEDOT:PSS films on the EML caused by their poor wetting property have been completely removed using a dilution method. By diluting PEDOT:PSS solutions with ethanol and analyzing a wetting envelope, we found the optimized dilution condition (10:1) and fabricated highly efficient inverted PLEDs with the uniformly coated PEDOT:PSS HIL, showing a current efficiency of 9.73 cd/A at 1000 cd/m2 and uniform light emission simultaneously.