Search

A new bilayer electrospun nanofiber membranes consisting of a hydrophobic silver nanoparticle-based polyimide nanocomposite (Ag-PI) supporting layer and hydrophilic poly(vinyl alcohol) (PVA) barrier layer for oily wastewater treatment application has been presented. First of all, the Ag-PI electrospun nanofibrous supporting layer was fabricated through electrospinning and thermal treatment from polyamic acid containing silver carbamate. After that, the PVA electrospun nanofibrous barrier layer was constructed by electrospinning onto the supporting layer and chemical crosslinked. The silver nanoparticles were uniformly formed through thermal-reduction of silver carbamate in nanofiber, homogeneously. The constructed bilayer electrospun nanofiber membranes were characterized by the permeate flux, rejection rate, and antimicrobial activity of Escherichia coli and Staphylococcus aureus. It was found that they showed strong antimicrobial activity as well as a high flux and high rejection rate at low operating pressure.

Although emergence of bone tissue engineering techniques has revolutionized the field of maxillofacial reconstruction, the successful translation of such products, especially concerning larger sized defects, still remains a significant challenge. Light-curable methacrylate-based polymers have ideal properties for bone repair. These materials are also suitable for 3D printing which can be applicable for restoration of both function and aesthetics. The main objective of this research was to synthesize a mechanically stable and biologically functional polymer for reconstruction of complex craniofacial defects. The experimental work initially involved synthesis of (((3R,3aR,6S,6aR)-hexahydrofuro[3,2-b]furan-3,6-diyl)bis(oxy))bis(ethane-2,1-diyl)bis((4-methyl-3-oxopent-4-en-1-yl)carbamate), CSMA-1, and ((((((((((((3R,3aR,6S,6aR)-hexahydrofuro[3,2-b]furan-3,6-diyl)bis(oxy))bis(ethane-2,1 diyl))bis(oxy))bis(carbonyl))bis(azanediyl))bis(methylene))bis(3,3,5-trimethylcyclohexane-5,1-diyl))bis(azanediyl))bis(carbonyl))bis(oxy))bis(ethane-2,1-diyl)bis(2-methylacrylate), CSMA-2; nuclear magnetic resonance analysis confirmed formation of the monomers, and composite samples were fabricated respectively by exposing 11 mm diameter discs to blue light. Modulus of elasticity was determined using a biaxial flexural test and the values were found to be between 1 and 3 GPa in CSMA-1, CSMA-2, and their composites. In vitro cell culture, using human bone marrow-derived mesenchymal stem cells, confirmed nontoxicity of the samples and finally 3D printing allowed direct photo-polymerization and setting of the bio ink into a 3D construct.

Three-dimensional (3D) printing enhances the production of on-demand fabrication of patient-specific devices as well as anatomically fitting implants with high complexity in a cost-effective manner. Additive systems that employ vat photopolymerisation such as stereolithography (SLA) and digital light projection (DLP) are used widely in the field of biomedical science and engineering. However, additive manufacturing methods can be limited by the types of materials that can be used. In this study, we present an isosorbide-based formulation for a polymer resin yielding a range of elastic moduli between 1.73 GN/mm2 dependent on the photoinitiator system used as well as the amount of calcium phosphate filler added. The monomer was prepared and enhanced for 3D-printing using an SLA technique that delivered stable and optimized 3D-printed models. The resin discussed could potentially be used following major surgery for the correction of congenital defects, the removal of oral tumours and the reconstruction of the head and neck region. The surgeon is usually limited with devices available to restore both function and appearance and with the ever-increasing demand for low-priced and efficient facial implants, there is an urgent need to advance new manufacturing approaches and implants with a higher osseointegration performance.

The novel electron-transporting moiety of 2,7-diazacarbazole was used to construct a bipolar host molecule for phosphorescent organic light-emitting diodes (PHOLEDs). This moiety was incorporated with typical hole-transporting carbazole moieties to synthesize a 2,7-diazacarbazole/carbazole hybrid called 9-(3,5-bis(carbazol-9-yl)phenyl)–2,7-diazacarbazole. The hybrid exhibits a high triplet energy above 2.88 eV and very high glass transition temperature of Tg = 148°C. It shows good thermal stability owing to the rigid nature of its symmetrical bipolar structure. The 2,7-diazacarbazole-based host material turns on at 3.6 and 3.7 V and approaches external quantum efficiencies above 16.0 and 22.6% in blue and green PHOLEDs, respectively. These results demonstrate that 2,7-diazacarbazole should be an excellent electron-transporting unit for bipolar phosphorescent hosts.

A new method was studied to efficiently metallize silk fabrics, and silver-coated silk fabrics were prepared and characterized. In this study, silver 2-ethylhexylcarbamate was used as the silver precursor, and a hydrogen atmosphere was used to reduce the precursors, thus forming silver nanoparticles on the surface of silk fabric. The silver-coated silk fabric was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy, and the results confirmed that 20-70 nm silver nanoparticles were uniformly generated without damaging the silk fabric. The silver-coated silk fabric showed excellent ultraviolet blocking properties and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This method provides a way to improve the antibacterial ability of silk fabrics while avoiding damage to the silk.

Starburst-type hole-transporting and electron-transporting materials, tris(3-(9H-carbazol-9-yl)phenyl)amine ( TmCTA ), 2,4,6-tri([1,1′-biphenyl]-3-yl)-1,3,5-triazine (1), 2,4,6-tris(3′-methyl-[1,1′-biphenyl]-3-yl)-1,3,5-triazine (2), and 2,4,6-tris(3′,5′-dimethyl-[1,1′-biphenyl]-3-yl)-1,3,5-triazine (3) having high triplet energies and excellent thermal stabilities were synthesized. Deposited films of TmCTA , with 1, 2, or 3 as hosts, were doped with the blue phosphorescent dopant bis[2-(4,6-difluorophenyl)pyridinato-C2 ,N](picolinato)iridium(III) (FIrpic) and their device characteristics were evaluated. In co-deposited films, the molecular weight ratio of TmCTA to 1, 2, or 3 was 1: 1, and these co-hosts formed exciplexes. By comparison with those of single-host systems, the PL spectra of the co-deposited films were red-shifted, suggesting that exciplexes are formed by the two constituent molecules. When doped with 10% FIrpic, TmCTA :1 device showed an external quantum efficiency (EQE) of 14.56% (maximum 16.46%) at 1000 cd/m2; similar results were obtained for the remaining films. The EQE roll-offs in the co-host systems are much smaller than those of single-host device using TmCTA .

To enhance the efficiency of organic light-emitting diodes (OLEDs), the application of triplet excitons must be maximized. Two donor–acceptor-type molecules bearing bis-carbazolyl and tris-carbazolyl groups at the ortho position of a phenyl-attached triazine ring were synthesized. These molecules showed very small singlet–triplet energy gaps (ΔE ST ) of 0.06 and 0.03 eV, respectively, and transient photoluminescence (PL) characteristics, which indicate that they are thermally activated delayed fluorescence (TADF) materials. A high external quantum efficiency (EQE) of 16.5% with deep blue color coordinates of (0.15, 0.22) was observed using a TrisCz–Trz TADF emitter. This interaction between the electron donor and electron acceptor substituents plays a key role in achieving a very small ΔE ST and good intramolecular charge transfer (ICT) activities with high photoluminescence (PL).

Novel mCP analogues consisting of blue phosphorescent host materials with fused-ring, 1,3-bis(5 H -benzofuro[3,2- c ]carbazol-5-yl)benzene (BFCz) and 1,3-bis(5 H -benzo[4,5]thieno[3,2- c ]carbazol-5-yl)benzene (BTCz) were designed and synthesized using benzofurocarbazole and benzothienocarbazole donor moieties. BFCz and BTCz exhibit high glass transition temperatures of 147 and 157 °C, respectively, and high triplet bandgaps of 2.94 and 2.93 eV, respectively. To explore the electroluminescence properties of these materials, multilayer blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated in the following device structure: indium–tin-oxide (ITO)/PEDOT:PSS/4,4’-cyclohexylidene bis[ N,N -bis(4-methylphenyl)aniline] (TAPC)/1,3-bis( N -carbazolyl) benzene (mCP)/host:FIrpic/diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1)/LiF)/Al. The PHOLEDs with BTCz exhibited efficient blue emission with luminous and quantum efficiencies of 30.9 cd/A and 15.5% at 1000 cd/m 2 , respectively.

For skeletal muscle engineering, scaffolds that can stimulate myogenic differentiation of cells while possessing suitable mechanical properties (e.g. flexibility) are required. In particular, the elastic property of scaffolds is of importance which helps to resist and support the dynamic conditions of muscle tissue environment. Here, we developed highly flexible nanocomposite nanofibrous scaffolds made of polycarbonate diol and isosorbide-based polyurethane and hydrophilic nano-graphene oxide added at concentrations up to 8%. The nano-graphene oxide incorporation increased the hydrophilicity, elasticity, and stress relaxation capacity of the polyurethane-derived nanofibrous scaffolds. When cultured with C2C12 cells, the polyurethane–nano-graphene oxide nanofibers enhanced the initial adhesion and spreading of cells and further the proliferation. Furthermore, the polyurethane–nano-graphene oxide scaffolds significantly up-regulated the myogenic mRNA levels and myosin heavy chain expression. Of note, the cells on the flexible polyurethane–nano-graphene oxide nanofibrous scaffolds could be mechanically stretched to experience dynamic tensional force. Under the dynamic force condition, the cells expressed significantly higher myogenic differentiation markers at both gene and protein levels and exhibited more aligned myotubular formation. The currently developed polyurethane–nano-graphene oxide nanofibrous scaffolds, due to their nanofibrous morphology and high mechanical flexibility, along with the stimulating capacity for myogenic differentiation, are considered to be a potential matrix for future skeletal muscle engineering.

Objective Although bisphenol A-glycidyl methacrylate (Bis-GMA)-based dental materials are widely used in dentistry, Estrogenicity from released bisphenol A remains a concern due to possibility of adversely affecting the growth of children and homeostasis of adults. Here, a new family of isosorbide-derived biomonomers were synthesized and experimentally utilized as a matrix of dental sealants to provide physico-mechanical and biological properties comparable to those of a conventional Bis-GMA-based material but without the the potential estrogenicity. Methods After synthesis of isosorbide-derived biomonomers (ISDB) by light polymerization, an experimental dental sealant with different silica filler concentrations (0–15 wt%) was characterized and compared to a commercially available Bis-GMA-based sealant. Cytotoxicity and estrogenicity assays were conducted with human oral keratinocytes and estrogen-sensitive MCF-7 cells, respectively. Results ISDB-based dental sealants exhibited typical initially smooth surfaces with depth of cure, Vickers hardness, compressive strength/modulus, water resorption/solubility, and flowability comparable to those of the commercial sealant and met the ISO standard for dental sealants and polymer-based restorative materials. Indirect cytotoxicity tests using an extract showed comparable viability among experimental ISDB-based materials and a commercial Bis-GMA-incorporated control. DNA synthesis in MCF-7 cells (a marker of estrogenicity) and the release of bisphenol A under enzymatic incubation were not detected in ISDB-based materials. Significance In conclusion, the comparable physico-mechanical properties of ISDB-based materials with their cytocompatibility and lack of estrogenicity suggest the potential usefulness of ISDBs as a newly developed and safe biomaterial.

In this paper, silver nanoparticle (AgNP)-coated cotton wool with sustained antibacterial properties was produced using a convenient solution-dipping method that involves soaking the cotton in a silver 2-ethylhexylcarbamate solution, followed by thermal reduction at 120℃. The silver-coated cotton was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction patterns. AgNPs with a uniform and high deposition density formed on the surface of the cotton and ranged in size from 20 to 80 nm. The antibacterial activity, blood clotting, and other physical properties, such as saline absorption and ultraviolet (UV)-blocking of Ag/cotton wool with different silver content were examined. All Ag/cotton fabrics exhibited excellent antibacterial activity against Staphylococcus aureus and Escherichia coli. AgNP-loaded cotton demonstrated faster blood clotting rates and better absorption of 0.9% (w/v) saline solution than unmodified cotton. In addition, AgNP-loaded cotton showed excellent UV protection properties.

Blue thermally activated delayed fluorescent (TADF) emitters were developed by linking a donor moiety to a triazine core via the ortho -position of an aromatic moiety. Three phenylcarbazole derivatives with different substituents were incorporated into the 4,6-diphenyltriazine core to prepare the blue TADF emitters. The photophysical properties and device performance of the blue TADF emitters were investigated, and the blue TADF emitters with 3,6-dimethyl-9-phenylcarbazole as the donor moiety showed a high quantum efficiency of 14.7%.

In this study, the surface of polyester fiber was modified by means of thermal treatment with a silver carbamate complex. We used scanning electron microscopy (SEM), an X-ray diffraction technique (XRD), and X-ray photoelectron spectroscopy (XPS) to allow a detailed characterization of the silver-coated polyethylene terephthalate (PET) fibers. The results revealed remarkable changes in the surface morphology and microstructure of the silver film after thermal reduction. On SEM, the silver nanoparticles (AgNPs) were seen to be uniformly and densely deposited on the fiber surface. The XRD pattern of the silver-coated fiber indicated that the film has a crystalline structure. A continuous layer of AgNPs, between 30 and 100 nm in size, was assembled on the PET fibers. The PET/Ag composite was found to impart high conductivity to the fibers, with an electrical resistivity as low as 0.12 kΩ·cm.

Shape memory polyurethanes (SMPUs) have attracted much attention in the biomedical field because they can easily control the transition temperature (Ttrans) to shape memory and are biocompatible. In this study, a shape memory polyurethane with both biocompatibility and a Ttrans close to the body temperature was synthesized by using natural derivatives of isosorbide and castor oil in place of petroleum-based materials. Isosorbide and castor oil were used to form net points, and polycaprolactone diol (PCL diol) acted as the switching segment. The synthesized four polyurethane (PCL diol/isosorbide/castor oil, PICU-1, 2, 3, 4) with different isosorbide contents exhibited desired thermal and mechanical properties. In the thermo-cyclic shape memory testing experiment, the PICU series demonstrated good shape memory property, with more than 95% shape recovery ratio (Rr) and more than 90% shape fixity ratio (Rf), and PICU-3 recovered its shape within 20 s in a 37 °C water bath. In addition, the PICU series proved to be safe materials with excellent biocompatibility, as indicated by the observed C2C12 cells viability and proliferation. The stent made with the PICU-3 film showed near complete magnetization at 37 °C within 18 s and proved to be a suitable self-expanding stent.

Graphene oxide as a radon barrier in living environments was introduced by intercalating the polymer resin-coated layer inside a multilayer membrane with an area of 1 × 10 m and a thickness of 2.5 mm, prepared by the roll-to-roll method. A 5 μm-thick graphene oxide polymer resin (GOPR) layer was coated on polyethylene terephthalate (PET) film (100 μm) between the two styrene-butadiene-styrene (SBS)-modified bitumen asphalt layers fitted for construction sites. The inserted graphene oxide materials were characterized by means of infrared, Raman, and X-ray photoelectron spectroscopy (XPS). Dispersion-corrected density functional theory (DFT) calculations suggested weaker binding energies on the oxide surfaces and higher penetration energy barriers of graphene nanopores for radon (222Rn) than in the cases of the atmospheric gas molecules Ar, H2O, CO2, H2, O2, and N2. Theoretical calculations of the graphene nanopores supported the higher barrier energies of 222Rn than most ambient gases. The roll-to-roll prepared graphene materials exhibited good barrier properties for 222Rn as well as for the ambient gases. The purpose of our experimental and theoretical study is to provide a better understanding of using graphene-based materials to reduce the risk of carcinogenic radon gas in construction sites and residential buildings for practical applications.

Highly efficient sky-blue organic light emitting devices (OLEDs) were fabricated using fused-ring spiro host materials 1,10-di(2-naphthyl)spiro[benzo[ij]tetraphene-7,9′-fluorene] ( H1 ) and 1-[1-(4-biphenyl)]-10-phenylspiro[benzo[ij]tetraphene-7,9′-fluorene] ( H2 ). H1 and H2 were doped with a fluorescent dopant based on 5,9-di(di-p-tollylaminospiro[benzo[c]fluorene-7,9′-fluorene] ( D3 ). Typical blue fluorescent OLEDs were fabricated with indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis[4-(phenyl-m-tolyl-amino)phenyl]-biphenyl-4,4′-diamine (DNTPD)/N,N,N′,N′-tetra(1-biphenyl)-biphenyl-4,4′-diamine (TBB)/ SBTF hosts: D3 /9,10-di(naphthalene-2-yl)anthracen-2-yl-(4,1-phenylene)(1-phenyl-1H -benzo[d]imidazole) (LG201)/LiF/Al configuration and were subsequently investigated. The H1 : 5% D3 device exhibited an electroluminescent emission at 472 nm, with efficiency 6.91 cd/A, external quantum efficiency 4.56% at 107.84 mA/cm2, and a sky-blue color at Commission Internationale de l′Eclairage (CIE) (x,y) coordinates of (0.150, 0.217) at 7447 cd/m2.

Zinc oxide nanoparticles (ZnO NPs) were synthesized in 2-methoxyethanol without assistance of base, surfactant, template, etc., at relatively low temperature of 125 °C, by a single-step thermolysis. Thermolysis of Zn(IBC)2 led to the formation of almost pure ZnO NPs of various shapes. Transmission electron microscope (TEM) images showed that oleic acid–stabilized ZnO NPs with diameters of 10–20 nm were well dispersed in organic solvent. Resulting ZnO was characterized by UV–vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, and high-resolution TEM. Room temperature photoluminescence (PL) spectra of ZnO NPs annealed at different temperatures showed different emission peaks in the range of 400–700 nm. The ZnO NPs prepared at 125 °C in air caused a further shift of the defect-related PL maximum toward the lower energy range (red-light emission) in comparison with the one prepared at 125 °C in 2-methoxyethanol.

This study describes a coating technique approach for large-scale preparation of sintered silver nanosheets whose lateral dimensions were controlled in the thickness range of 50–65 nm. These procedures involved coating water-soluble poly (vinyl alcohol) (PVA) and silver 2-ethylhexylcarbamate (Ag-EHC), as well as thermal reduction of a silver precursor by heating at 150 °C, followed by dissolving away the PVA layer with alcoholic water. When the silver carbamate layer on the PVA layer was heated to 150 °C, the silver carbamate layer was thermally reduced and directed to grow into uniform sintered nanosheets with aspect ratios as high as 1000. The multi-stacked PVA/Ag structures and sintered silver nanosheets were confirmed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Measurements of the conductive property at room temperature indicated that these nanosheets were electrically continuous with a resistivity of approximately 7.3 × 10−6 Ω cm.

New blue fluorescent spirobenzoanthracene-type dopant materials, 3,9-di(di(p-tolyl))aminospiro[benzo[de]anthracene-7,9′-fluorene] (DTSBAF) and 3,9-di(di(4-biphenyl))aminospiro[benzo[de]anthracene-7,9′-fluorene] (DBSBAF), were designed and successfully prepared by an amination reaction of 3-bromo-9-chlorospiro[benzo[de] anthracene-7,9′-fluorene] with di(p-tolyl)amine and di(4-biphenyl)amine, respectively. The EL characteristics of 1,10-dinaphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (DNSBTF) as the blue host material doped with the above blue dopant materials was evaluated. The electroluminescence spectra of indium tin oxide (150 nm)/N,N′-diphenyl-N,N′-bis[4-(phenyl-m-tolyl-amino)phenyl]-biphenyl-4,4′-diamine (DNTPD, 60 nm)/N,N,N′,N′-tetra(1-biphenyl)-biphenyl-4,4′-diamine (TBB, 30 nm)/SBTF hosts: SBAF dopant (20 nm, 5%)/9,10-di(naphthalene-2-yl)anthracen-2-yl-(4,1-phenylene)(1-phenyl-1H-benzo[d]imidazole) (LG201, 20 nm)/LiF (1 nm)/Al (200 nm) with DNSBTF as a host material show a blue emission band with a full width at half maximum of 50 nm and λmax = 472 nm. The device obtained from DNSBTF doped with DTSBAF showed a good color purity (0.141, 0.254), high luminance efficiency (10.12 cd A−1 at 5 V) and high external quantum efficiency (6.02%).

Thermally responsive shape-memory polymers have received widespread attention in the biomedical field. In this study, biocompatible and biodegradable polyurethane (PU) and polycaprolactone (PCL) were blended to obtain shape-memory properties. Highly crystalline PCL was used as a hard segment, and PU synthesized from isosorbide, which is non-toxic and chemically and thermally stable, was used as a soft segment. The obtained PU/PCL blends containing the 30%, 50%, and 70% PU by weight were investigated for their thermal properties, mechanical properties, and shape-memory behavior. The 30%PU/PCL polymer has the best shape-memory characteristics and can be knotted by itself in the hot water bath, indicating that it can be applied in smart suture applications. The degradation test performed at 37 °C in phosphate buffered solution showed a mass loss of 2–4% for the obtained PU/PCL blends after 6 weeks. Finally, MC3T3-E1 cells cultured on PU/PCL blends showed high biocompatibility due to high adhesion and proliferation.

A simple strategy was developed based on a new monomer, 2-[4-[2-(4-pyridyl)vinyl]phenoxy]ethyl methacrylate (PVPEM), comprising 4-styrylpyridine to obtain both photocurable and attachable polyelectrolyte to a gold electrode. Humidity-sensing membranes are composed of copolymers of [2-(methacryloyloxy)ethyl] dimethyl propyl ammonium bromide (MEPAB), PVPEM and methylmethacrylate, followed by thiolation. The purpose was to crosslink and to anchor the polyelectrolyte to the gold electrode. Polyelectrolyte inks were formulated. The resulting sensors which used printing methods reduced the deflection of sensor characteristics showing a humidity precision ±0.9%RH. The humidity sensor with copolymer MEPAB/PVPEM/MMA = 60/10/30 showed a good sensitivity changing the resistance approximately four orders of magnitude including relative humidity varying from 20 to 95%RH and also a fast response and recovery time. The resultant sensors showed a good linearity and small hysteresis. The reliability including water resistance and a long-term stability were estimated for the application of the flexible humidity sensor.

E-mail: msgong@dankook.ac.krReceived March 12, 2014, Accepted April 3, 2014We have successfully decorated reduced graphene oxide (RGO) with silver nanoparticles (AgNPs) bymicrowaving silver alkylcarbamate for 13 seconds using 1-amino-4-methylpiperazine. Uniform AgNPs (20–40 nm) were effectively prepared, and 1-amino-4-methylpiperazine acted as a reaction medium, reducingagent, and stabilizer. Particle size and morphology were correlated with the silver alkylcarbamate concentrationand microwave time. The graphene/AgNPs composites were characterized by Raman, X-ray diffraction, andscanning electron microscopy to confirm that the AgNPs were uniformly decorated onto the graphene.Measurements of the transparent conductive property at room temperature indicated that these graphene/AgNPs nanosheets with 55.45% transmittance were electrically continuous with a sheet resistance ofapproximately 43 kΩ/

Blue light-emitting spiro[benzotetraphene-fluorene] (SBTF)-based host materials, 3-(1-naphthyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9'-fluorene] (1), 3-(2-naphthyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9'-fluorene] (2), and 3-[2-(6-phenyl)naphthyl]-10-naphthylspiro[benzo[ij]tetraphene-7,9'-fluorene] (3) were designed and prepared via multi-step Suzuki coupling reactions. Introducing various aromatic groups into SBTF core lead to a reduction in band gap and a determination of the color purity and luminescence efficiency. Typical sky-blue fluorescent organic light emitting diodes with the configuration of ITO/N,N'-di(1-naphthyl)-N,N'-bis[(4-diphenylamino)phenyl]-biphenyl-4,4'-diamie (60 nm)/N,N,N',N'-tetra(1-biphenyl)-biphenyl-4,4'-diamine (30 nm)/host: dopant (30 nm, 5%)/LG201 (electron transporting layer, 20 nm)/LiF/Al were developed using SBTF derivatives as a host material and p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) as a sky-blue dopant material. A device obtained from three materials doped with DSA-Ph showed color purity of 0.148 and 0.239, a luminance efficiency of 7.91 cd/A, and an external quantum efficiency >4.75% at 5 V.

E-mail: mgong@dankook.ac.krReceived April 8, 2013, Accepted June 17, 2013We examined the effect of electrode fingers and gaps of coplanar interdigitated electrode (IDE) structures tocharacterize the ammonium salt-containing polyelectrolyte film of resistance-based humidity sensors. IDEsdesigned for this purpose were flexible gold electrodes deposited on a polyimide substrate using a printingprocess because the geometry presents a potential for tunable sensitivity over other electrode designs. The basicdesign of the sensors consisted of IDEs with a different number of electrode fingers such as 3, 4, and 5 and gapsizes of 310, 360, 410, and 460 µm. Details of the AC complex impedance characteristics such as the Nyquistplot, Bode plot, and activation energy based on electrode construction were investigated. Key Words : Resistive humidity sensor, Bode plot, Nyquist plot, Interdigitated electrode, Electrode patternIntroductionHumidity sensors have attracted increasing attention becauseof the growing demand for accurate measurement and con-trol of environment humidity in many fields.

Resistive humidity sensors based on an epoxy interpenetrating polymer network (IPN) polyelectrolyte films, which had strong adhesion to polyimide substrate, were developed for flexible polyimide electrode. Humidity sensitive epoxy IPN films were prepared using two stage cross-linking between the diglycidyl ether of bisphenol-A (DEGEBA) and a phosphate ester curing agent (EPEs), followed by photocuring of copolymer of 2-(cinnamoyloxy)ethyl methacryate (CEMA) and [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (METAC). Under optimal conditions ([METAC/CEMA]/[DGEBA/EPEs] = 2/1), a semi-log graph of film resistance was plotted linearly by four orders of magnitude (from 10 3 to 10 7 Ω) on increasing humidity over a humidity range of 20–95%RH and exhibited good linearity ( Y = −0.0529 X + 7.8048, R 2 = −0.9944). Furthermore, reliability testing (in terms of water resistance and high temperature, humidity, and long-term stabilities) of the epoxy IPN/gold electrode/polyimide substrate showed that they are satisfactory for use as flexible humidity sensors.

A novel flexible resistive-type humidity sensor was fabricated by printing a pair of comb-like gold electrodes on a polyimide (PI) film, followed by printing with copolymers made of [2-[(methacryloyloxy)ethyl] dimethyl]propylammonium bromide (MEPAB), methyl methacrylate (MMA), and 2-(cinnamyloxy)ethyl methacryate (CEMA) as a humidity-sensing film. The self-crosslinkable polyelelctrolyte copolymers contained different contents of MEPAB/MMA/CEMA = 70/27/3, 70/25/5, 70/23/7, and 70/20/10. A gold electrode was pretreated with 2-(mercaptoethyl) cinnamamide (MEC) containing a thiol-coupling agent for the purpose of anchoring the humidity-sensitive polyelectrolyte to the gold electrode on the flexible PI substrate. UV irradiation on the humidity-sensitive film stimulated a crosslinking reaction between the cinnamate and cinnamamide groups via [2π+2π] addition. After soaking in water for 60 min, the resulting sensor using MEC showed water durability and increased resistance of 42–65%, corresponding to a reduction in relative humidity of 2.25–2.98%RH. The flexible humidity sensor also showed good hysteresis (−1.1 to −0.8%RH), an acceptable response time (97 s), and good stability at high temperature and high humidity.