Room‐Temperature Phosphorescence From Films of Isolated Water‐Soluble Conjugated Polymers in Hydrogen‐Bonded Matrices

It is well known that luminescent conjugated polymers suffer serious loss of photoluminescence quantum yield (PLQY) in the solid state compared to dilute solution. This is due to efficient exciton migration in the solid, which enables the excitons to readily find low energy quenching sites. Here a new method to fabricate solid films with densely packed non‐interacting luminescent polymer chains, which yield very high PLQY and more astonishingly room temperature phosphorescence, is reported. Using water‐soluble conjugated polymers (WSCP) and polymeric surfactants such as poly(vinyl alcohol) (PVA) and poly(vinyl‐pyrrolidone) (PVP), films at 1:1 wt% or higher WSCP are produced and show room temperature phosphorescence; such behavior has never been observed before and clearly shows the very high degree of chain isolation that can be achieved in these hosts. The PVA or PVP not only breaks up WSCP aggregates in solution as an effective surfactant, PVA‐PVA or PVP‐PVP hydrogen bond formation upon drying locks in the isolation of the WSCP, avoiding segregation and yielding long time stability to these polymer/polymer nanomixtures. The method is found to work with a wide variety of WSCPs.     

Optical assessment of a fouling-resistant surface (PHEMA/ benzalkonium chloride) after exposure to a marine environment

A hydrogel based on poly(2-hydroxyethyl methacrylate) (PHEMA) containing benzalkonium chloride (BAK) can be used as an environmentally acceptable, fouling-resistant material in the marine environment. The loaded hydrogel system is transparent and has the potential to be used in the protection of optical ports in underwater instruments. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of the material after a marine exposure period. The optical transmittance of PHEMA/ BAK was higher for 10 weeks than that detected for poly(methyl methacrylate) (PMMA), a material currently used in commercial instruments, which confirmed the superior fouling resistance of the PHEMA/ BAK combination. The UV–vis spectroscopic method was quick, relatively cheap and accurate enough to allow the effects of the development of marine fouling on transparent surfaces for use in marine underwater optical applications to be monitored. © 1998 John Wiley & Sons, Ltd.     

Blood‐Inert Surfaces via Ion‐Pair Anchoring of Zwitterionic Copolymer Brushes in Human Whole Blood

A strategy to create blood‐inert surfaces in human whole blood via ion‐pair anchoring of zwitterionic copolymer brushesand a systematic study of how well‐defined chain lengths and well‐controlled surface packing densities of zwitterionic polymers affect blood compatibility are reported. Well‐defined diblock copolymers, poly(11‐mercaptoundecyl sulfonic acid)‐block‐poly(sulfobetaine methacrylate) (PSA‐b‐PSBMA) with varying zwitterionic PSBMA or negatively charged PSA lengths, are synthesized via atom‐transfer radical polymerization (ATRP). PSA‐b‐PSBMA is grafted onto a surface covered with polycation brushes as a mimic polar/hydrophilic biomaterial surface via ion‐pair anchoring at a range of copolymer concentrations. Protein adsorption from single‐protein solutions, 100% blood serum, and 100% blood plasma onto the surfaces covered with PSA‐b‐PSBMA brushes is evaluated using a surface plasmon resonance sensor. Copolymer brushes containing a high amount of zwitterionic SBMA units are further challenged with human whole blood. Low protein‐fouling surfaces with >90% reduction with respect to uncoated surfaces are achieved with longer PSA blocks and higher concentrations of PSA‐b‐PSBMA copolymers using the ion‐pair anchoring approach. This work provides a platform to achieve the control of various surface parameters and a practical method to create blood‐inert surfaces in whole blood by grafting ionic‐zwitterionic copolymers to charged biomaterials via charge pairing.     

Engineering a Robust,Versatile Amphiphilic Membrane Surface Through Forced Surface Segregation for Ultralow Flux‐Decline

Unlike biofoulants/pollutants, oil foulants/pollutants are prone to coalesce, spread and migrate to form continuous fouling layer covering on the surfaces. Therefore, such kind of fouling can not be simply alleviated by hydrophilic modification with currently extensively used antifouling materials such as poly(ethylene glycol) (PEG)‐based or zwitterionic polymers etc. In the present study, an amphiphilic porous membrane surface, comprising hydrophilic fouling resistant domains and hydrophobic fouling release microdomains, is explored via a "forced surface segregation" approach. The resultant membranes exhibit both superior oil‐fouling and bio‐fouling resistant property: membrane fouling is exquisitely suppressed and the permeation flux‐decline is decreased to an ultralow level. It can be envisaged that the present study may open a novel avenue to the design and construction of robust, versatile antifouling surfaces.     

Tunable Chemical and Topographic Patterns Based on Binary Colloidal Crystals (BCCs) to Modulate MG63 Cell Growth

More effective and diversified surface modification strategies are required for materials used in biomedical engineering. Combining surface modification involving bioactive signals or nonfouling polymers with tunable topography has the potential to meet this need. Here, a method is reported to generate bioactive surfaces having tunable topographies based on self‐assembled binary colloidal crystals (BCCs), where the colloids are premodified with nonfouling molecules or cell adhesive peptides. The BCCs are fabricated from silica (Si) microspheres and polymer nanospheres. The Si microspheres are either modified with poly(ethylene glycol) (PEG) or with the cell adhesive arginine–glycine–aspartic acid (RGD) peptide prior to BCC fabrication. Four types of BCCs are explored in cell studies using MG63 cells. BCC surfaces coupled with PEG or RGD peptides are found to significantly modulate cell adhesion, spreading, and morphology, which is attributed to the combination of BCC topography and the molecules at the particle surface within the BCC. PEG‐modified BCCs are expected to find applications where limited cell adhesion is required, while the RGD‐modified BCCs have the potential for enhancing cell growth on medical devices such as bone implants. More advanced cell biology applications such as controlled stem cell differentiation are also anticipated to find use from BCCs.     

Towards Thermoconductive,Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers

Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20‐fold thermal conductivity improvement in BNNT‐containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT‐loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat‐releasing materials.     

Removal of Microparticles by Ciliated Surfaces—an Experimental Study

Biological cilia are versatile hair‐like organelles that are very efficient in manipulating particles for, e.g., feeding, antifouling, and cell transport. Inspired by the versatility of cilia, this paper experimentally demonstrates active particle‐removal by self‐cleaning surfaces that are fully or partially covered with micromolded magnetic artificial cilia (MAC). Actuated by a rotating magnet, the MAC can perform a tilted conical motion, which leads to the removal of spherical particles of different sizes in water, as well as irregular‐shaped sand grains both in water and in air. These findings can contribute to the development of novel particulate manipulation and self‐cleaning/antifouling surfaces, which can be applied, e.g., to prevent fouling of (bio)sensors in lab‐on‐a‐chip devices, and to prevent biofouling of submerged surfaces such as marine sensors and water quality analyzers.     

Active Enzyme Nanocoatings Affect Settlement of Balanus amphitrite Barnacle Cyprids

Balanus amphitrite cyprids produce complex adhesive substances that enable their attachment to surfaces and impart a strong detachment resistance from most immersed substrata. The colonization of man‐made structures by barnacle cyprids and other marine organisms is a troublesome and costly phenomenon, for which controlling strategies are actively sought. In this work, we expand previous investigations about the susceptibility of cyprid adhesives to unpurified proteases in solution by evaluating the interplay between these secreted biomolecules and a surface‐confined purified protease. The strategy involved the covalent immobilization of the enzyme Subtilisin A to maleic anhydride copolymer thin films through the spontaneous reaction of anhydride moieties with lysine side chains. This enabled the production of bioactive layers of tunable enzyme surface concentration and activity, which were utilized to systematically evaluate the effect of the immobilized enzyme on cyprid settlement and exploratory behavior. Surfaces of increasing enzyme activity displayed a gradual decrease in cyprid settlement levels (approaching inhibition) as well as an increase in post‐settlement adhesion failure (evidenced by significant numbers of detached metamorphosed individuals). High activities of the bound enzyme also affected pre‐settlement behavior of cyprids, reducing the velocity and total distance moved while increasing the amount and speed of meander compared to the controls. The here‐reported low enzyme surface concentrations found to be remarkably effective at reducing cyprid settlement hold promise for the use of immobilized enzymes in the control of marine biofouling.     

Dynamic Fluoroalkyl Polyethylene Glycol Co‐Polymers: A New Strategy for Reducing Protein Adhesion in Lab‐on‐a‐Chip Devices

Non‐specific adsorption of biomolecules (or “biofouling”) is a major problem in microfluidics and many other applications. The problem is particularly pernicious in digital microfluidics (DMF, a technique in which droplets are manipulated electrodynamically on an array of electrodes coated with a hydrophobic insulator), as local increases in surface energy that arise from fouling can cause droplet movement to fail. We report a new solution to this problem: a device coating bearing a combination of fluorinated poly(ethylene glycol) functionalities (FPEG) and perfluorinated methacrylate (FA) moieties. A range of different FPEG‐FA copolymers were synthesized containing varying amounts of FPEG relative to the fluorinated backbone. Coatings with low%FPEG were found to result in significant reductions in protein adsorption and improvements in device lifetime (up to 5.5‐fold) relative to the state of the art. An analysis of surface topology and chemistry suggests that FPEG‐FA surfaces undergo a dynamic reconstruction upon activation by applying DMF driving potentials, with FPEG groups forming vertical protrusions out of the plane of the device surface. An analysis of changes in surface wettability and adhesion as a function of activation supports this hypothesis. This innovation represents an advance for digital microfluidics, and may also find use in other applications that are currently limited by biofouling.     

Vertically Segregated Structure and Properties of Small Molecule–Polymer Blend Semiconductors for Organic Thin‐Film Transistors

A comprehensive structure and performance study of thin blend films of the small‐molecule semiconductor, 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene (diF‐TESADT), with various insulating binder polymers in organic thin‐film transistors is reported. The vertically segregated composition profile and nanostructure in the blend films are characterized by a combination of complementary experimental methods including grazing incidence X‐ray diffraction, neutron reflectivity, variable angle spectroscopic ellipsometry, and near edge X‐ray absorption fine structure spectroscopy. Three polymer binders are considered: atactic poly(α‐methylstyrene), atactic poly(methylmethacrylate), and syndiotactic polystyrene. The choice of polymer can strongly affect the vertical composition profile and the extent of crystalline order in blend films due to the competing effects of confinement entropy, interaction energy with substrate surfaces, and solidification kinetics. The variations in the vertically segregated composition profile and crystalline order in thin blend films explain the significant impacts of binder polymer choice on the charge carrier mobility of these films in the solution‐processed bottom‐gate/bottom‐contact thin‐film transistors.     

Siloxane Copolymers for Nanoimprint Lithography

Presented here is the novel use of thermoplastic siloxane copolymers as nanoimprint lithography (NIL) resists for 60 nm features. Two of the most critical steps of NIL are mold release and pattern transfer through dry etching. These require that the NIL resist have low surface energy and excellent dry‐etching resistance. Homopolymers traditionally used in NIL, such as polystyrene (PS) or poly(methyl methacrylate) (PMMA), generally cannot satisfy all these requirements as they exhibit polymer fracture and delamination during mold release and have poor etch resistance. A number of siloxane copolymers have been investigated for use as NIL resists, including poly(dimethylsiloxane)‐block‐polystyrene (PDMS‐b‐PS), poly(dimethylsiloxane)‐graft‐poly(methyl acrylate)‐co‐poly(isobornyl acrylate) (PDMS‐g‐PMA‐co‐PIA), and PDMS‐g‐PMMA. The presence of PDMS imparts the materials with many properties that are favorable for NIL, including low surface energy for easy mold release and high silicon content for chemical‐etch resistance—in particular, extremely low etch rates (comparable to PDMS) in oxygen plasma, to which organic polymers are quite susceptible. These properties give improved NIL results.     

Printed,Flexible, Organic Nano‐Floating‐Gate Memory: Effects of Metal Nanoparticles and Blocking Dielectrics on Memory Characteristics

The effects of using a blocking dielectric layer and metal nanoparticles (NPs) as charge‐trapping sites on the characteristics of organic nano‐floating‐gate memory (NFGM) devices are investigated. High‐performance NFGM devices are fabricated using the n‐type polymer semiconductor, poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2)), and various metal NPs. These NPs are embedded within bilayers of various polymer dielectrics (polystyrene (PS)/poly(4‐vinyl phenol) (PVP) and PS/poly(methyl methacrylate) (PMMA)). The P(NDI2OD‐T2) organic field‐effect transistor (OFET)‐based NFGM devices exhibit high electron mobilities (0.4–0.5 cm² V^?1 s^?1) and reliable non‐volatile memory characteristics, which include a wide memory window (≈52 V), a high on/off‐current ratio (I_on/I_off ≈ 10⁵), and a long extrapolated retention time (>10⁷ s), depending on the choice of the blocking dielectric (PVP or PMMA) and the metal (Au, Ag, Cu, or Al) NPs. The best memory characteristics are achieved in the ones fabricated using PMMA and Au or Ag NPs. The NFGM devices with PMMA and spatially well‐distributed Cu NPs show quasi‐permanent retention characteristics. An inkjet‐printed flexible P(NDI2OD‐T2) 256‐bit transistor memory array (16 × 16 transistors) with Au‐NPs on a polyethylene naphthalate substrate is also fabricated. These memory devices in array exhibit a high I_on/I_off (≈10^{4 ± 0.85}), wide memory window (≈43.5 V ± 8.3 V), and a high degree of reliability.     

The Fabrication and Characterization of Single‐Component Polymeric White‐Light‐Emitting Diodes

By using Ni⁰‐mediated polymerization, we have systematically synthesized a series of fluorene‐based copolymers composed of blue‐, green‐, and red‐light‐emitting comonomers with a view to producing polymers with white‐light emission. 2,7‐Dibromo‐9,9‐dihexylfluorene, {4‐(2‐[2,5‐dibromo‐4‐{2‐(4‐diphenylamino‐phenyl)‐vinyl}‐phenyl]‐vinyl)‐phenyl}‐diphenylamine (DTPA), and 2‐{2‐(2‐[4‐{bis(4‐bromo‐phenyl)amino}‐phenyl]‐vinyl)‐6‐tert‐butyl‐pyran‐4‐ylidene}‐malononitrile (TPDCM) were used as the blue‐, green‐, and red‐light‐emitting comonomers, respectively. It was found that the emission spectra of the resulting copolymers could easily be tuned by varying their DTPA and TPDCM content. Thus with the appropriate red/green/blue (RGB) unit ratio, we were able to obtain white‐light emission from these copolymers. A white‐light‐emitting diode using the polyfluorene copolymer containing 3 % green‐emitting DTPA and 2 % red‐emitting TPDCM (PG3R2) with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/PG3R2/Ca/Al was found to exhibit a maximum brightness of 820 cd m^–2 at 11 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33,0.35), which are close to the standard CIE coordinates for white‐light emission (0.33,0.33).     

Graphite Oxide as an Olefin Polymerization Carbocatalyst: Applications in Electrochemical Double Layer Capacitors

Graphite oxide (GO) is shown to be an efficient heterogeneous catalyst for the polymerization of various olefin monomers, including n‐butyl vinyl ether, N‐vinylcarbazole, styrene, and sodium 4‐styrenesulfonate. The GO‐catalyzed polymerization of n‐butyl vinyl ether (0.1–5.0 wt% GO relative to monomer) proceeds rapidly under solvent‐free conditions and affords polymers with moderate number average molecular weights and broad polydispersities. Analysis of the carbon recovered at the conclusion of the polymerization reactions reveals that the material's catalytic activity is retained and multiple polymerization cycles can be performed without regenerating the catalyst. GO also catalyzes the polymerization of N‐vinylcarbazole and styrene, although only low molecular weight polymers are obtained. Sodium 4‐styrenesulfonate polymerizes in the presence of GO to afford poly(sodium 4‐styrenesulfonate) (PSS) composites. After thermal treatment, the composites can be fabricated into electrodes for use in electrochemical double layer capacitors (EDLCs). The devices display high specific capacitances (25–120 F g^?1) and low equivalent series resistances (14–27 Ω).     

Stalking the Materials Genome: A Data‐Driven Approach to the Virtual Design of Nanostructured Polymers

Accelerated insertion of nanocomposites into advanced applications is predicated on the ability to perform a priori property predictions on the resulting materials. In this paper, a paradigm for the virtual design of spherical nanoparticle‐filled polymers is demonstrated. A key component of this “Materials Genomics” approach is the development and use of Materials Quantitative Structure‐Property Relationship (MQSPR) models trained on atomic‐level features of nanofiller and polymer constituents and used to predict the polar and dispersive components of their surface energies. Surface energy differences are then correlated with the nanofiller dispersion morphology and filler/matrix interface properties and integrated into a numerical analysis approach that allows the prediction of thermomechanical properties of the spherical nanofilled polymer composites. Systematic experimental studies of silica nanoparticles modified with three different surface chemistries in polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(2‐vinyl pyridine) (P2VP) are used to validate the models. While demonstrated here as effective for the prediction of meso‐scale morphologies and macro‐scale properties under quasi‐equilibrium processing conditions, the protocol has far ranging implications for Virtual Design.     

Organic Thin‐Film Transistors: Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers (Adv. Funct. Mater. 8/2011)

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

Slippery Liquid‐Infused Porous Surfaces that Prevent Microbial Surface Fouling and Kill Non‐Adherent Pathogens in Surrounding Media: A Controlled Release Approach

Many types of slippery liquid‐infused porous surfaces (‘SLIPS’) can resist adhesion and colonization by microorganisms. These ‘slippery’ materials thus offer approaches to prevent fouling on commercial and industrial surfaces. However, while SLIPS can prevent fouling on surfaces to which they are applied, they can currently do little to prevent the proliferation of non‐adherent organisms. Here, multi‐functional SLIPS are reported that address this issue and expand the potential utility of these materials. The approach is based on the release of antimicrobial agents from the porous matrices used to host the infused oil phases. It is demonstrated that SLIPS fabricated from nanoporous polymer multilayers can prevent colonization and biofilm formation by four common fungal and bacterial pathogens, and that the polymer and oil phases comprising these materials can be used to sustain the release of triclosan, a model antimicrobial agent, into surrounding media. This approach improves the inherent anti‐fouling properties of these materials and endows them with the ability to kill non‐adherent pathogens. This strategy has the potential to be general; the strategies and concepts reported here will enable the design of SLIPS with improved anti‐fouling properties and open the door to new applications of slippery liquid‐infused materials that host or release other active agents.     

Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

Electron‐Rich Alcohol‐Soluble Neutral Conjugated Polymers as Highly Efficient Electron‐Injecting Materials for Polymer Light‐Emitting Diodes

We report the design and synthesis of three alcohol‐soluble neutral conjugated polymers, poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF‐OH), poly[9,9‐bis(2‐(2‐(2‐diethanol‐aminoethoxy)ethoxy)ethyl)fluorene‐alt‐4,4′‐phenylether] (PFPE‐OH) and poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene‐alt‐benzothiadizole] (PFBT‐OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light‐emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron‐deficient polymer (PFBT‐OH) shows very poor electron‐injecting ability compared to polymers with electron‐rich main chain (PF‐OH and PFPE‐OH). This phenomenon is quite different from that obtained from conventional electron‐injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs.     

Uniformly Shaped Poly(p‐phenylenediamine) Microparticles: Shape‐controlled Synthesis and Their Potential Application for the Removal of Lead Ions from Water

A novel method for the shape‐controlled synthesis of uniformly‐shaped poly(p‐phenylenediamine) (PpPD) microparticles with different morphologies under ambient condition has been developed using HAuCl₄ as an oxidant and poly(N‐vinylpyrrolidone) (PVP) as a surfactant. The results demonstrate that the morphologies of these microparticles can be varied from symmetrical spindle‐like to diamond‐like, centrosymmetric leaf‐like, and parallelogram‐like by tuning the concentration of reactants and their molar ratios. The length of these microparticles varies from 6 to 8 µm while the width can be tuned from 2 to 4 µm. The results demonstrate that PVP as a surfactant only plays a role in controlling the morphology of the polymer particles but has no influence on the polymer structures. UV‐Vis absorption spectroscopy shows the formation of a complex between polymer ligands and lead ions by detection of new absorption peaks. Even though the as‐prepared PpPD microparticles are only partly soluble, they still show an adsorptive affinity for lead ions.