Drying stability enhancement of red-perovskite colloidal ink via ligand-derived coating for inkjet printing

Today, inkjet printing techniques has many merits such as high printing yield and mask-free process for the various field. As one of the candidate ink materials, the perovskite is appropriate for inkjet printing due to the colloidal state and excellent optoelectronic properties such as high photoluminescence quantum yield (PLQY) and narrow full width at half maximum (FWHM). Those characteristics are an advantage to fabricating ink and realize wide color-gamut in the small area with micro-patterning. However, perovskite application in inkjet printing with various color has limitations due to the low drying stability of mixed halide perovskite.Herein, we report on improving the drying stability of red perovskite by inducing aggregation during the drying process. Silane ligand has applied to induce the aggregation, and we confirmed that the thin coating layer has formed on the perovskite surface. The synthesized red-perovskite using silane ligands is well dispersed in the solvent as a colloidal state. And it maintained the emission intensity over 50% after drying. As-prepared perovskite ink has successfully printed on the ethyl cellulose film with 338 dpi with maintaining transparency of the film. These results are beneficial not only display applications but also security applications such as double anti-counterfeiting.     

Construction of Micro-Patterned Polymer Structures by Piezoelectric Inkjet Printing

It is not simple to accurately deposit minute quantities of polymeric materials by inkjet printing systems. High viscosity, nozzle clogging, agglomeration, precipitation, and uncontrollable drying patterns are serious problems which are frequently encountered in polymer inkjet printing. In this study, we investigated how inkjet printability of polymers correlates with the polymer ink formulations and inkjet process variables. After a systematic study with different variables, various patterns such as dots, cross stripes, and honeycombs were fabricated on flexible polyimide (PI) films and the pattern morphology and spatial distribution of the resulting polymer deposits after solvent drying were characterized.     

Optimizing inkjet printing process to fabricate thick ceramic coatings

This article describes the use of Taguchi optimization and ANOVA techniques on inkjet printing process to determine optimal parameters for fabrication of thick ceramic coatings over glass substrates. Stable nanoparticle suspensions are synthesized through high energy milling of precursor powders with adequate quantities of binder and suspending solvent. Most often, inkjet printing process is being used for developing fine and thin layers (<10 µm). However, an attempt is made to fabricate thick ceramic films by varying only IJP process parameters and without multiple layer deposition, thereby reducing efforts in ink synthesis and processing time of coated substrates. Three parameters of IJP were varied for developing a model that was used for precisely predicting the printed layer thickness under varying process parameters. ANOVA technique showed that open time interval in combination with nano particle concentration in the ink could potentially lead to thick coatings. The higher volume % of solvent in the diluted suspension ink under the influence of substrate heating contributed significantly to coffee stain effect with irregular surface coatings. However, increasing the concentration of nanoparticles in the diluted ink resulted in substantial improvement in thickness of the layer with simultaneous control of coating defects.     

The nanostructure and dewetting of block copolymer thin films annealed in different neutral solvents

The morphology of polystyrene‐b‐poly(2‐vinyl pyridine) thin films annealed under various neutral solvents was investigated. The morphological transition depends on the vapor pressure of the solvent, the quantity of the solvent in the film, and annealing time. We introduced the volume fraction of solvent in a film (Q) to correlate these factors to the morphology. At low Q, the amount of solvent that penetrates into the film is limited and it cannot induce enough chain mobility. Thus, thin film shows short stripes or a worm‐like structure. At high Q, the great diffusion of solvent into the film facilitates polymer mobility, leading to an ordered structure. Our results also suggested that the dewetting mechanism of thin film depends on Q. At low Q, dewetting develops via the nucleation and growth. At high Q, the condensation of solvent on the surface removes some polymer and dewetting is dominated by spinodal mechanism. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Formation and characterization of perfluorocyclobutyl polymer thin films

Perfluorocyclobutyl (PFCB) polymers are a new class of materials that show promise as selective layer materials in the development of composite membranes for gas separations, such as carbon dioxide/methane (α_{pure gas} = 38.6) and oxygen/nitrogen (α_{pure gas} = 4.8) separations. In many of the flat sheet applications, a thin film of the selective layer that is free of major defects must be coated onto a support membrane. A focus of this study was to elucidate the impacts of solvents, polymer concentration, and dip‐coating withdrawal speed on PFCB thin film thickness and uniformity. An extension was proposed to the Landau–Levich model to estimate the polymer film thickness. The results show that the extended model fits the thickness‐withdrawal speed data well above about 55 mm/min, but, at lower withdrawal speeds, the data deviated from the model. This deviation could be explained by the phenomenon of polymer surface excess. Static surface excesses of polymer solutions were estimated by applying the Gibbs adsorption equation using measured surface tension data. Prepared films were characterized by ellipsometry. Refractive index was found to increase with decreasing film thickness below about 50 nm, indicating densification of ultrathin films prepared from PFCB solutions below the overlap concentration. Atomic force microscopy was used to characterize surface morphologies. Films prepared from tetrahydrofuran and chloroform yielded uniform nanolayers. However, films prepared using acetone as solvent yielded a partial dewetting pattern, which could be explained by a surface depletion layer of pure solvent between the bulk PFCB/acetone solution and the substrate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Novel Insights into Inkjet Printed Silver Nanowires Flexible Transparent Conductive Films

Silver nanowire (AgNWs) inks for inkjet printing were prepared and the effects of the solvent system, wetting agent, AgNWs suspension on the viscosity, surface tension, contact angle between ink droplet and poly(ethylene) terephthalate (PET) surface, and pH value of AgNWs ink were discussed. Further, AgNWs flexible transparent conductive films were fabricated by using inkjet printing process on the PET substrate, and the effects of the number printing layer, heat treatment temperature, drop frequency, and number of nozzle on the microstructures and photoelectric properties of AgNWs films were investigated in detail. The experimental results demonstrated that the 14-layer AgNWs printed film heated at 60 °C and 70 °C had an average sheet resistance of 13 Ω∙sq⁻¹ and 23 Ω∙sq⁻¹ and average transparency of 81.9% and 83.1%, respectively, and displayed good photoelectric performance when the inkjet printing parameters were set to the voltage of 20 V, number of nozzles of 16, drop frequency of 7000 Hz, droplet spacing of 15 μm, PET substrate temperatures of 40 °C and nozzles of 35 °C during printing, and heat treatment at 60 °C for 20 min. The accumulation and overflow of AgNWs at the edges of the linear pattern were observed, which resulted in a decrease in printing accuracy. We successfully printed the heart-shaped pattern and then demonstrated that it could work well. This showed that the well-defined pattern with good photoelectric properties can be obtained by using an inkjet printing process with silver nanowires ink as inkjet material.     

Carbazole‐based electroluminescent devices obtained by vacuum evaporation

Transparent conductive oxide (SnO₂)/organic layers/aluminum thin film sandwich structures were obtained by vacuum evaporation. The organic component was either a thin carbazole film or a bilayer. In that case, the carbazole film was deposited onto a thin insulating polymer film. The polymer used was the poly(tetrabromo‐p‐phenyleneselenide) (PBrPDSe). Photoluminescence measurements have shown that the carbazole thin films emit blue light. (I‐V) measurements have shown that the structures exhibit diode characteristics. The forward direction is obtained when the transparent conductive oxide (TCO) is positively biased. However, the reproducibility of the results obtained with a single carbazole layer is poor. It appears that the stability of the sample is improved when a thin PBrPDSe film (40 nm) is introduced between the carbazole and the SnO₂. The polymer film avoids the short circuit effect. In that case, the turn‐on voltage of the diode is about 3 V, when the thickness of the carbazole film is around 250 nm and the electroluminescence appears at a voltage of about 5 V. It is shown that the thermionic effect cannot be used to explain the I‐V characteristics, which are interpreted with the help of the Fowler–Nordheim tunnel effect. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2042–2055, 2001     

Amorphous silicon–carbon based nano-scale thin film anode materials for lithium ion batteries

The buffering effect of carbon on the structural stability of amorphous silicon films, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin film (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin films, denoted as a-C/Si, has been investigated. In comparison to pure amorphous Si thin film (a-Si) which shows a rapid fade in capacity after 30 cycles, the a-C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 μA/cm² (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a-Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a-Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a-C/Si thin film during the alloying/dealloying process with lithium has been confirmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin film battery systems.     

The morphology, electrical conductivity and vapour sensing ability of inkjet-printed thin films of single-wall carbon nanotubes

Thin films containing single-wall carbon nanotubes (SWCNTs) have been prepared using the inkjet printing (IJP) technique. Atomic force microscopy (AFM) has been used to investigate the morphology of these layers. The inkjet printed films consisted of small, randomly-oriented islands of nanotubes, the topography of which was dependent on the nature of the substrate surface. The in-plane electrical characteristics of the films were measured at room temperature. The current versus voltage data exhibited non-linear behaviour, which could be fitted to the theoretical model for Poole-Frenkel conductivity. Preliminary measurements are also reported on the use of the thin layers to detect alcohol vapour.     

Reactive inkjet printing of polyethylene glycol and isocyanate based inks to create porous polyurethane structures

Reactive inkjet printing offers a direct way to create polymeric structures in situ on a substrate. Therefore, two component polyurethane formulations can be utilized to be used in multicomponent inkjet printing. In this contribution, the use of polyethylene glycol (M = 200 g mol⁻¹), glycerol ethoxylate (M = 1,000 g mol⁻¹), and water (blowing agent) in combination with aliphatic 1,6-hexamethylene diisocyanate or aromatic methylene diphenyl diisocyanate for reactive inkjet printing is evaluated. The inks are jettable on a Dimatix DMP-3000 inkjet printer using a 10 pL piezo driven drop-on-demand printhead showing stable droplet formation. Solid films on glass are formed using a drop-by-drop printing strategy. Layer-by-Layer strategy gives best results on polycarbonate substrates forming porous polyurethane structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46977.     

Fumaryl chloride and maleic anhydride–derived crosslinked functional polymers for nonlinear optical waveguide applications

The synthesis, processing, and characterization of new crosslinked functional polymer thin films derived from fumaryl chloride and maleic anhydride is presented. Experimental data demonstrated that this is a versatile, convenient, and cost‐effective method of fabricating ultrastructure crosslinked and functional polymer thin films for potential nonlinear optical (NLO) or other applications where molecular orientation is required. The unsaturated and processable polyester thin films are capable of crosslinking in air to form a hardened lattice under a variety of conditions, including both thermal and photoinitiated crosslinking. The thermal stability of the second harmonic (SHG) signal for a crosslinked NLO thin film was stable at temperatures up to 150°C, which is in contrast to uncrosslinked polymers whose SHG signals typically decreased over 50% below 100°C. Because of the lack of NH/OH groups and their vibrational overtones in the polymer, these crosslinked polyester systems have a great potential for low optical loss applications at 1550 nm communication wavelength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 317–322, 2004     

The synthesis and evaluation of cyclic olefin sulfone copolymers and terpolymers as electron beam resists

Poly(cyclopentene sulfone) (PCPS) and poly(bicycloheptene sulfone) (PBCHS) copolymers have been evaluated as potential positive electron beam resists which have good thermal properties and which show high sensitivity to ionizing radiation. It was found that thin copolymer films could be processed as resists but that films greater than 3000 Å thick cracked in the solvents used to dissolve the radiation-exposed regions. Incorporation of plasticizing additives did not improve the film properties. Films from low molecular weight polymer fractions cracked less in solvents, but higher radiation doses were required to offset the reduced sensitivity. This resulted in the formation of intractable residues in the exposed regions which appear to be crosslinked polymer. Bicycloheptene monomers with specific functional groups did not improve the properties of the copolymer films. Terpolymerization with α-olefins such as butene-1 and cis-2-butene plasticized these films and reduced their tendency to crack in solvents. Poly(cyclopentene sulfone–co–butene-1 sulfone) films were found to have the best properties, and 1.25-μ resist images could be etched in SiO₂ layers at an exposure dose of 4 × 10^?6 C/cm² at 25KV. However, one important limitation of this terpolymer was the low dissolution rate ratio between the exposed and unexposed regions. Since straight-walled relief images are essential to the formation of high-resolution patterns, the usefulness of this terpolymer as an electron beam resist appears to be hindered by the limited choice of good solvents to maximize the dissolution rate ratio. PBCHS block terpolymers containing methyl methacrylate (MMA) or methacrylic acid (MAA) were synthesized to improve the solubility in solvents and to incorporate the properties of methacrylates. PBCHS–MMA films cracked in solvents after irradiation; PBCHS–MAA polymers were too insoluble to form resist films.     

Solvent penetration and photoresist dissolution: A fluorescence quenching and interferometry study

A novel method, based upon fluorescence quenching measurements, is described for the study of the mechanistic details of solvent penetration into thin polymer films. Here poly(methyl methacrylate) (PMMA) labelled with phenanthrene (Phe) groups was coated as a film (0.8 μm thick) onto quartz disks. Diffusion of solvent (1 : 1 2-butanone/2-propanol) into the film was followed by a decrease in Phe fluorescence, while film dissolution was monitored simultaneously by laser interferometry. In the case of PMMA (M_w = 411,000, films annealed at 160°C) both processes occur at approximately the same rate and exhibit non-Fickian (relaxation-controlled) diffusion behavior. Correlating the results of these two experiments shows that, once the steady state is reached, the dissolution rate is controlled by the advance of the solvent front into the PMMA film. The “transition layer,” an important dissolution parameter, increases its thickness from 50 to 90 nm during the plasticization stage of solvent penetration and maintains its thickness until the solvent front reaches the quartz substrate.     

Preparation and characterization of carboxymethyl konjac glucomannan/sodium montmorillonite hybrid films

Carboxymethyl konjac glucomannan (CKGM)/ sodium montmorillonite (MMT) hybrid films of various compositions were prepared by casting from a polymer/silicate water suspension. The structure and properties of the hybrid films were investigated by wide angle X‐ray diffraction (WAXD), transmission electron microscopy (TEM), attenuated total reflection infrared spectroscopy (ATR‐IR), differential scanning calorimetry (DSC), and tensile tests. The results from WXRD and TEM indicated that an intercalated CKGM/MMT nanocomposite film was obtained by polymer solution intercalation. WXRD and DSC showed that the high‐T_m crystal phase was induced by the presence of lower MMT loading, but the T_m of the hybrid films became weak with the increase of MMT content due to the polymer confinement. The hybrid films showed higher thermal stability and mechanical properties than that of the neat polysaccharide due to the strong interaction between hydroxyl and carbonyl group of CKGM and the silicate layer of MMT. Furthermore, the degree of swelling of the hybrid films was investigated in acidic buffer solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2954–2961, 2007     

Insoluble porous conjugated polymer films via phase separation and photo‐crosslinking for the trace detection of 2,4‐dinitrotoluene

A novel conjugated polymer film with microscale/submicroscale porous morphology fabricated from crosslinked poly(fluorene‐co‐carbazole) (PFC1) was developed for the detection of 2,4‐dinitrotoluene (DNT). The fluorescent conjugated polymer PFC1 with pendant photo‐crosslinkable coumarin groups was synthesized by Suzuki coupling polymerization. Taking advantage of the phase separation of PFC1/polystyrene (PS) blends in the film and the solvent‐resistant network, porous structured films were prepared by removal of PS. Films with porous morphologies exhibited marked responsive sensitivity to trace DNT vapor due to the unique porous structure favoring the diffusion of and association with DNT molecules. The formation of a crosslinked network by dimerization of the coumarin moieties may be beneficial for isolating the polymeric backbones, thus to some extent preventing chain aggregation. This facile fabrication method enabled the crosslinked porous films to be efficient fluorescence chemosensors towards the detection of trace amounts of DNT vapor.© 2012 Society of Chemical Industry     

General formula for bending beam determination of case II diffusion in polymer-containing bilayer structures

An exact formula has been presented to correlate the bending curvature cariation ratio, Ω, of any given bilayer structure comprising a solvent-swellable polymer layer with diffusion time, t, under case II diffusion. The formula can be used to determine the diffusion front velocity, v, for layered structures comprising a thick polymer film on a thin substrate or vice versa when subjected to solvent diffusion. According to this formula, there is little effect from plasticization or swelling in the transverse direction on the diffusion curve of Ω vs. t if the polymer layer to be investigated is relatively thin and its intrinsic hygroscopic strain ratio is less than unity. By using this model, the diffusion of N-methyl pyrollidinone (NMP) in a 18-μm rodlike pyromellitic dianhydride p-phenylene-diamine (PMDA-PDA) polymide film, coated on a 75-μm silicon substrate, is found to be case II with a diffusion front velocity of 1.84 × 10^-7 cm/s. © 1995 John Wiley & Sons, Inc.     

Surface modification of coil coatings with thin plasma polymer films structure and stability

Plasma deposition of a thin top layer with tailored properties is an effective strategy of modification of the organic coating surface. Thin plasma polymer layers are candidates and can provide superior hardness, scratch resistance, modified surface hydrophobicity and easy to clean properties.The present work studies the stability of thin plasma polymer films deposited as top layer on polyurethane coil coating systems. Microwave, hollow cathode and radio frequency plasma polymerization reactors were employed in order to deposit a thin SiO_x based plasma polymer layer.The plasma film stability was studied using surface analysis techniques, ex situ and in situ atomic force microscopy and scanning electron microscopy. Energy dispersive spectroscopy, FTIR spectroscopy and optical measurements confirm the composition and plasma layer properties. The structure of the plasma layers was investigated by means of transmission electron microscopy.The surface morphology together with composition evolution allows the study of the stability of the different coatings. The structure examination of the formed plasma polymer film offers good clarification for coating failure. Decrease of the operating pressure during plasma polymerization and oxygen concentration in precursor mixture lead to formation of compacter layer with higher stability. Introduction of fluorine-containing precursor also increases the anti-weathering performance of the plasma polymer films.     

Hygienic coatings by UV curing of diacrylic oligomers with added triclosan

Hygienic coatings have been obtained by UV photopolymerization of mixtures of urethane-diacrylate, tri-propylene-glycol diacrylate and 2,4,4′-trichloro-2′-hydroxydiphenylether (Triclosan). UV-dried coatings containing a weight fraction of Triclosan as low as 0.001 submitted to tests for antimicrobial activity evaluation with Escherichia coli colonies have shown the complete elimination of living bacteria in the thin liquid layer in contact with the film surface. A persistent biocide activity can also be observed after a prolonged water treatment of the coating. The biocide release from the coating has been studied through contact with water–ethanol mixtures of different compositions. The maximum release rate has been observed at an ethanol weight fraction of 0.85, where the crosslinked films show the maximum swelling. The phenomena can be explained on the basis of the interaction between the liquid and the polymer network through the Hansen solubility parameters.     

A Novel Polymeric Substrate with Dual-Porous Structures for High-Performance Inkjet-Printed Flexible Electronic Devices

Inkjet printing has emerged as a promising low-cost and high-performance method for manufacturing printing-based devices. However, the development of optimized substrates for inkjet printing using novel materials is limited. In this study, a novel polymeric substrate optimized for flexible electronic devices is fabricated using thin-film processing and phase inversion of polyethersulfone (PES). The PES film consists of two layers of pores; the upper layer has nano-sized pores that filter the nanoparticles in the conductive ink and allow for high-density aggregation on the substrate, while the lower layer contains micro-scale pores that quickly absorb and drain the ink solvent. The two porous structures lead to higher conductivity and high-resolution printed patterns by minimizing solvent lateral diffusion. Additionally, the PES printing substrate can undergo high-temperature curing of metal nanoparticles, enabling high-resolution pattern printing with low resistance. The PES substrate is highly transparent and flexible, allowing for the fabrication of various printed electronic patterns and the production of high-performance flexible electronic devices.     

Aqueous Solution‐Processable,Flexible Thin‐Film Transistors Based on Crosslinked Chitosan Dielectric Thin Films

The hydrophilic character of chitosan (CS) limits its use as a gate dielectric material in thin‐film transistors (TFTs) based on aqueous solution‐processable semiconductor materials. In this study, this drawback is overcome through controlled crosslinking of CS and report, for the first time, its application to aqueous solution‐processable TFTs. In comparison to natural CS thin films, crosslinked chitosan (Cr‐CS) thin films are hydrophobic. The dielectric properties of Cr‐CS thin films are explored through fabrication of metal–insulator–metal devices on a flexible substrate. Compared to natural CS, the Cr‐CS dielectric thin films show enhanced environmental and water stabilities, with a high breakdown voltage (10 V) and low leakage current (0.02 nA). The compatibility of Cr‐CS dielectric thin films with aqueous solution‐processable semiconductors is demonstrated by growing ZnO nanorods via a hydrothermal method to fabricate flexible TFT devices. The ZnO nanorod‐based TFTs show a high field‐effect mobility (linear regime) of 10.48 cm² V^?1 s^?1. Low temperature processing conditions (below 100 °C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e‐waste problem.