Atmospheric pressure plasma liquid deposition of copper nanoparticles on poly(4-vinylpyridine)-grafted-poly(tetrafluoroethylene) surface and their autocatalytic properties

We demonstrate catalyst-free electroless deposition of copper on a poly(4-vynylpyrridine)-grafted-poly(tetrafluoroethylene) surface. The principle of this process relies on deposition of an organo-copper(II) precursor film on the functionalized polymer surface and on subsequent plasma-assisted reduction of the copper ion to form nanoparticles. A polymer surface densely and homogeneously seeded with copper nanoparticles enable to initiate autocatalytic electroless deposition of copper layer without need for any prior sensitizing the surface with conventionally used SnCl₂ and Pd species.     

Evaluation of electrospun fibrous scaffolds of poly(dl-lactide) and poly(ethylene glycol) for skin tissue engineering

This study is derived from the innate concerns of electrospun poly(DL-lactide) (PDLLA) fibers as tissue engineering scaffolds: hydrophobic surface, surface erosion and dimensional shrinkage, which are not favorable to trigger the initial adhesion and further growth and population of cells. Blending electrospinning of PDLLA and poly(ethylene glycol) (PEG) with different PEG contents was evaluated for optimal tissue engineering scaffolds. The surface hydrophilicity was improved, and the degradation patterns of PDLLA/PEG mats changed from surface erosion to bulk degradation with the increase in PEG contents. The dimensional shrinkage was alleviated through the formation of crystal regions of PEG in the fiber matrix. The PDLLA/PEG fibrous mats were slightly weakened with the increase in the PEG contents, but a significant decrease in the tensile strength could be found for those with PEG contents of over 40%. Human dermal fibroblasts (HDFs) interacted and integrated well with the surrounding fibers containing 20 and 30% PEG, which provided significantly better environment for biological activities of HDFs than electrospun PDLLA mats. It indicated that electrospun mats containing 30% PEG exhibited the most balanced properties, including moderately hydrophilic surface, minimal dimensional changes, adaptable bulk biodegradation pattern and enhancement of cell penetration and growth within fibrous mats.     

Consecutively spin-assembled layered nanoarchitectures of poly(sodium 4-styrene sulfonate) and poly(allylamine hydrochloride)

The recently established spin-coating electrostatic self-assembly (SCESA) technique has been shown to facilitate not only the rapid fabrication of polyelectrolyte multilayer assemblies, but also allow each layer to be easily controlled on a monomolecular scale by minimizing the film thickness across a substrate surface. In this paper, the influence of polyelectrolyte concentration on the amount and thickness of spin-deposited polymer films has been examined for a multilayer system of poly(allyamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), when the washing steps employed for removing weakly bound polyelectrolytes on a resultant film on a substrate are excluded from the standard fabrication procedure of the SCESA method. The thickness of the spin-deposited PAH/PSS bilayer increased linearly for the PSS concentrations in the range from 1 to 10 mM with PAH constant at 1 mM, which demonstrates the uniform deposition of each layer material onto the thin film. The thickness of PAH/PSS bilayers increased from 1.43 ± 0.06 to 3.37 ± 0.08 nm as the PSS concentration increased from 1 to 10 mM, while the PAH concentration was kept constant at 1 mM. The multilayer films were found to be stable in a good solvent (H₂O) for at least 30 h, without any noticeable loss of the adsorbed layer component of the polyelectrolyte. This improvement to the SCESA method (exclusion of washing steps) provides a convenient way to create multilayer heterostructures with the thickness of each layer being easily adjusted.     

Realization of porous poly(methyl methacrylate) films filled with electrodeposited carbon nanotubes

A deposition process on a conducting surface, in which water acted as the dispersed phase and a mixture of poly(methyl methacrylate) and chloroform as the continuous phase, was applied to prepare poly(methyl methacrylate) films. The influence of relative humidity during the film preparation on the surface morphology was investigated by field emission scanning microscopy. High-humidity preparation conditions lead to porous poly(methyl methacrylate) films. These films were then used as templates to perform the selective deposition into the pores of single-walled carbon nanotubes by an electrophoretic method. The attractive properties of carbon nanotubes combined with the versatile properties of poly(methyl methacrylate) open up new opportunities for these nanocomposites to achieve novel architectures in nanodevices and?microdevices.     

Efficient TCO-free organic solar cells with modified poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) anodes

Organic photovoltaic cells (OPVs) with a highly conductive poly 3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS) layer as an anode and that were modified with the addition of some organic solvents such as sorbitol (So), dimethyl sulfoxide (DMSO), N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), and ethylene glycol (EG) were fabricated without the use of transparent conducting oxide (TCO). The conductivity of the PEDOT:PSS film that was modified with each additive was enhanced by three orders of magnitude. According to the atomic force microscopy (AFM) study, the conductivity enhancement might have been related to the better connections between the conducting PEDOT chains. The TCO-free solar cells with a modified PEDOT:PSS layer and an active layer composed of poly (3-hexylthiophene) (P3HT) and phenyl [6, 6] C61 butyric acid methyl ester (PCBM) performed as well as the indium-tin-oxide (ITO)-based organic solar cells. The power conversion efficiency (PCE) of the organic solar cells with a DMSO-, So + DMSO-, and EG-modified PEDOT:PSS layer reached 3.51, 3.64, and 3.77%, respectively, under an illumination of AM 1.5 (100 mW/cm2).     

Evaluation of molecular orientation and alignment of poly(3-hexylthiophene) on Au (111) and on poly(4-vinylphenol) surfaces

The orientation and alignment of regioregular poly(3-hexylthiophene) (P3HT) molecules on Au (111) surface and on poly(4-vinylphenol) (PVP) thin film were investigated. The P3HT molecules on the smooth Au (111) are oriented with both the backbones and the side chains parallel to the substrate (plane-on orientation) as revealed by the scanning tunneling microscope (STM) images. However, the P3HT molecules on the PVP thin films are preferably oriented with side chains perpendicular to the surface (edge-on orientation). Surface modification of the PVP by hexamethyldisilazane (HMDS) can increase the crystalline size in the P3HT semicrystalline films. The performance of an all-polymer organic field-effect transistor (OFET) with the drop-cast P3HT semiconductor layer and the crosslinked PVP gate insulator on poly(ethylene naphthalate) (PEN) substrate was evaluated.     

Poly(dimethylsiloxane)-polyimide blends in the formation of thick polyimide films

Thick polyimide layers can be formed by using some unique properties of poly(dimethylsiloxane)-polyimide (PDMS/PMDA–ODA) blends followed by surface modification and deposition of a second layer of polyimide precursor chemicals. The method is based on the micro-phase separation characteristics of these blends to yield surfaces that have PDMS-like character. Upon modification with UV/ozone treatment, a surface that is essentially SiO _x and hydrophilic in nature is produced. This surface is amenable to reaction and deposition of a second polyimide layer from polyimide precursors. The thicker polyimide layer has enhanced adhesion between the original layer of the blend and the new polyimide layer and this approach finds extensive applications for products that require thick polymer layers. Changes in surface energy for various blend compositions were monitored by measurement of advancing contact angle with de-ionized water. Contact angle for unmodified polyimide films was on the order of 70° and it increased to about 104° after blending with PDMS and curing. UV/ozone treatment reduced the contact angle of the doped polyimide to less than 5°. X-ray photoelectron spectroscopy (XPS) and angle resolved XPS (ARXPS) measurements were used to monitor the chemical compositions of the various surfaces. High-resolution XPS spectra in the Si2p region confirm the transformation of O–Si–C bonds in PDMS to SiO _x , where x is about 2. Scanning electron microscopy (SEM) of some selected samples shows that the blends contain phase separation of the polymers at the surfaces of the samples. Atomic force microscopy (AFM) of siloxane-free polyimide, and PDMS/PMDA–ODA blends both prior to and after UV/ozone exposure, show that the films are essentially flat at short treatment times (less than 60 min). AFM also reveals the separation of PDMS into micro-domains at the cured film surface and throughout the layer below the surface of the blended films. Adhesion of a subsequently deposited polyimide layer to the modified polyimide surface was found to be greatly improved when compared to the adhesion obtained for deposition onto a pristine polyimide surface.     

Fabrication of conducting poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) thin films by ultrasonic spray-assisted mist deposition method

Transparent conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) thin films were fabricated by a vapor-deposition technique, ultrasonic spray-assisted mist deposition method. The thickness was well controlled from 40 to 600 nm, keeping reasonable conductivity of 300-450 S/cm. The films with thickness less than 180 nm have high (> 80%) transmission over a wide (270-800 nm) spectral region. In addition, formation of ring-dot electrode pattern with a hard-mask was demonstrated, achieving lithography-less patterning. The results encourage that this deposition method is developed as an actual process technology of transparent electrodes in devices.     

Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol)

Poly(ethylene glycol) (PEG) was ‘polymerized’ onto poly(ethylene terephthalate) (PET) surface by radio frequency (RF) plasma polymerization of PEG (average molecular weight 200 Da) at a monomer vapour partial pressure of 10 Pa. Thin films strongly adherent onto PET could be produced by this method. The modified surface was characterized by infra red (IR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-cut test, contact angle measurements and static platelet adhesion studies. The modified surface, believed to be extensively cross-linked, however showed all the chemical characteristics of PEG. The surface was found to be highly hydrophilic as evidenced by an interfacial free energy of about 0.7 dynes/cm. AFM studies showed that the surface of the modified PET became smooth by the plasma polymerized deposition. Static platelet adhesion studies using platelet rich plasma (PRP) showed considerably reduced adhesion of platelets onto the modified surface by SEM. Plasma ‘polymerization’ of a polymer such as PEG onto substrates may be a novel and interesting strategy to prepare PEG-like surfaces on a variety of substrates since the technique allows the formation of thin, pin-hole free, strongly adherent films on a variety of substrates.     

Photovoltaic characterization of hybrid solar cells using surface modified TiO(2) nanoparticles and poly(3-hexyl)thiophene

We report on the photovoltaic performance of bulk heterojunction solar cells using novel nanoparticles of 6-palmitate ascorbic acid surface modified TiO(2) as an electron acceptor embedded into the donor poly(3-hexyl)thiophene (P3HT) matrix. Devices were fabricated by using P3HT with varying amounts of red TiO(2) nanoparticles (1:1, 1:2, 1:3?w-w ratio). The devices were characterized by measuring current-voltage characteristics under simulated AM 1.5 conditions. Incident photon to current efficiency (IPCE) was spectrally resolved. The nanoscale morphology of such organic/inorganic hybrid blends was also investigated using atomic force microscopy (AFM).     

Surface modification of poly(3,4-ethylene dioxthiophene):poly(styrene sulfonic acid) (PEDOT:PSS) films by atmospheric-pressure argon plasma for organic thin-film solar cells

Highly-conductive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) films obtained by the addition of dimethylsulfoxide (DMSO) and the argon plasma exposure were used as a transparent conductive anode (TCA) for copper-phthalocyanine (CuPc)/C60 organic thin-film solar cells (OSCs). The CuPc/C60 OSCs on as-grown DMSO added PEDOT:PSS layer showed a power efficiency of 0.6%, whereas it was improved markedly to 1.34% after the atmospheric-pressure argon plasma exposure, which was comparable to that formed on indium-tin-oxide layer. Effects of the DMSO addition and the argon plasma exposure in the spin-coated PEDOT:PSS films is demonstrated in terms of the in-depth characterization of optical and electrical properties.     

Covalent micropatterning of poly(dimethylsiloxane) by photografting through a mask

A new photografting method to micropattern a covalent surface modification on poly(dimethylsiloxane) (PDMS) provides advantages in simplicity and efficiency. To accomplish the entire process on the benchtop, the PDMS was initially treated with benzophenone dissolved in a water/acetone mixture. This process permitted limited diffusion of the photoinitiator into the PDMS surface. Polymerization of acrylic acid was initiated by exposure of the benzophenone-implanted PDMS to UV radiation through a photomask with a thin aqueous layer of acrylic acid sandwiched between the PDMS and photomask. This procedure resulted in patterned poly(acrylic acid) (PAA) on the PDMS surface. In the modified regions, PAA and PDMS formed an interpenetrating polymer network extending 50 microm into the PDMS with an X-Y spatial resolution of 5 microm. The carboxyl groups of the PAA graft could be derivatized to covalently bond other molecules to the patterned PAA. Two bioanalytical applications of this micropatterned surface were demonstrated: (1) a guide for cell attachment and growth and (2) a substrate for immunoassays. 3T3 cells were shown to selectively localize to modified surface regions where they could be cultured for up to 7 days. Additionally, the micropatterned surface was used to immobilize either protein A or antibody for heterogeneous immunoassays.     

Moisture-induced hysteresis of pentacene thin film transistors with cross-linked poly(4-vinylphenol) gate dielectrics

The time variable electrical characteristics of pentacene thin-film transistors (TFTs) with poly(4-vinylphenol) gate dielectrics were investigated under various relative humidity conditions and the effect of moisture on the hysteresis behavior of the pentacene TFTs was studied. One possible cause of the hysteresis behavior is the presence of inherent hydroxyl groups in bulk or surface of the polymeric dielectric, which make the gate dielectric polar, but the hysteresis behavior of the pentacene TFTs was found to depend strongly on the relative humidity and to increase with an increase of the moisture in the surrounding atmosphere. With a time-scalable investigation, it was also found that the adsorption of moisture onto the pentacene layer is the main reason for the hysteresis even with the -OH rich polymeric dielectric. The hysteresis behavior was found to be significantly reduced by suppression of moisture or other moisture-induced impurities, such as the encapsulation of the devices with glass.     

Significant vertical phase separation in solvent-vapor-annealed poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) composite films leading to better conductivity and work function for high-performance indium tin oxide-free optoelectronics

In the present study, a novel polar-solvent vapor annealing (PSVA) was used to induce a significant structural rearrangement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films in order to improve their electrical conductivity and work function. The effects of polar-solvent vapor annealing on PEDOT:PSS were systematically compared with those of a conventional solvent additive method (SAM) and investigated in detail by analyzing the changes in conductivity, morphology, top and bottom surface composition, conformational PEDOT chains, and work function. The results confirmed that PSVA induces significant phase separation between excess PSS and PEDOT chains and a spontaneous formation of a highly enriched PSS layer on the top surface of the PEDOT:PSS polymer blend, which in turn leads to better 3-dimensional connections between the conducting PEDOT chains and higher work function. The resultant PSVA-treated PEDOT:PSS anode films exhibited a significantly enhanced conductivity of up to 1057 S cm(-1) and a tunable high work function of up to 5.35 eV. The PSVA-treated PEDOT:PSS films were employed as transparent anodes in polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs). The cell performances of organic optoelectronic devices with the PSVA-treated PEDOT:PSS anodes were further improved due to the significant vertical phase separation and the self-organized PSS top surface in PSVA-treated PEDOT:PSS films, which can increase the anode conductivity and work function and allow the direct formation of a functional buffer layer between the active layer and the polymeric electrode. The results of the present study will allow better use and understanding of polymeric-blend materials and will further advance the realization of high-performance indium tin oxide (ITO)-free organic electronics.     

To increase the lifetime of electroluminescent (EL) device by low-temperature deposition of organic thin solid films

We have studied the electrical and light-emitting behaviour as well as the lifetime of electroluminescent (EL) cells which consist of naphthoylimide (NPL) as the emitting layer and poly(3-octythiophene) (P3OT) doped with poly(N-vinylcarbazoe) (PVK) as the hole transport layer sandwiched between indium-tin-oxide (ITO) and aluminium (Al) electrodes. The mixed polymer (P3OT : PVK) layer and the emitting layer were deposited by spin coating and by vacuum deposition. When the ITO substrate was cooled to near liquid N2 temperature during the deposition of the NPL emitting layer, the brightness of the cells increased. Characterized by atomic force microscopy (AFM), the emitting layer became more amorphous as the deposition temperature decreased. Results collected show that low temperature deposition of organic thin solid films would be a powerful technique for not only the enhancement of electroluminescent brightness but also increasing the lifetime of EL devices. © 1998 Kluwer Academic Publishers     

Characterization and in vitro degradation of poly(octadecanoic anhydride)

Poly(octadecanoic anhydride) (POA) has been prepared by melt polycondensation of octadecanoic diacid. POA was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The results of in vitro degradation and SEM micrographs show that the erosion process of POA is neither bulk nor perfect surface erosion but rather has elements of both in phosphate buffer at 37 °C. The moving erosion front is characteristic of surface erosion whereas the remaining porous shell stems from bulk erosion. While a significant special degradation property of POA is that POA presents a very slow degradation rate in acidic condition (pH 5.98), only 1.64% weight loss for 20 days, and it completely degrades after 18 days in basic buffer (pH 7.4). Comparing with poly(sebacic anhydride) (PSA), POA has the higher crystallization degree, and the slower hydrolytic rate.     

Syntheses of titania and poly(3,4-ethylenedioxythiophene) bilayer nanotubes

Synthesis of bilayer tubes of poly(3,4-ethylenedioxythiophene) (PEDT) and titania by electrochemical polymerization of PEDT and chemical deposition of titania in the pores of anodic alumina was reported. Electron diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and fourier transformed infrared spectroscopy (FTIR) were used to characterize these bilayer tubes. SEM photographs show the tubes of uniform diameters around 200 nm. TEM photographs confirm the formation of titania and PEDT bilayer tubes of 230 nm and 100 nm diameter, the thickness of outside TiO2 layer and inner PEDT layer are around 20 nm under the experimental condition. The XPS spectra of the bilayer tubes show that the Ti2p peak shifts to a lower binding energy and S2p peak shifts to a higher binding energy. Electron diffraction patterns show that TiO2 nanotubes formed was single crystals of anatase phase. I-V characteristic curves were measured for samples prepared under various conditions.     

iCVD growth of poly(N-vinylimidazole) and poly(N-vinylimidazole-co-N-vinylpyrrolidone)

The imidazole group plays an important role in α-chymotrypsin catalysis, metal-ion complexation, counterion or dye binding. Poly(N-vinylimidazole), PVI, is also a good model polymer interacting with neutral salts. The poly(N-vinylimidazole-co-N-vinylpyrrolidone) copolymer P(VI-co-VP), can be used to produce highly functionalized polymers.PVI and P(VI-co-VP) thins films were achieved via initiated chemical vapor deposition (iCVD), a solvent-free process to form films under mild conditions. The polymerization was initiated by hot wire heated tert-butyl peroxide (TBPO). The chemical structure and compositions of the polymers were analyzed using FTIR and XPS. The growth rate of PVI as a function of the pressure inside the iCVD reactor was measured to be 1 nm/h mTorr. The XPS results show that the functional groups were retained in the polymer deposited. For the P(VI-co-VP) deposition, there are more VI groups found in the co-polymer chain even when the reacting monomers were fed in the same ratio.     

Formation and surface modification of self-assembled films with acrylated hyperbranched poly(ester-amine) as the outmost layer

An acrylated hyperbranched poly(ester-amine) (HPEA) synthesized from piperazine and trimethylolpropanetriacrylate at a molar ratio of 1:1.42 was used as the polycation to form self-assembled films by layer-by-layer dipping with poly(sodium-p-styrenesulfonate) as the polyanion. The surface morphology and hydrophilicity of the films with HPEA as the outmost layer were controlled by adjusting the solution pH of HPEA. Due to the existence of many acrylate groups, the films with HPEA as the outmost layer were further reacted with a series of reagents, including piperazine, piperidine, laurylamine and p-phenylenediamine. The surface reactions of the films depended on both the nature of the reagents and the morphology of the initial surface. In the presence of the strong basic amines, piperazine and piperidine, the films dissolved extensively into the solution. In the case of laurylamine, a modified film with an opaque appearance was obtained due to the crystallization of long alkyl chains. With the weak basic amine p-phenylenediamine as the reactant, the film was effectively modified without any change in the surface morphology.     

Electrodeposition of poly(o-anisidine) coatings onto copper

Abstract

Uniform and strongly adherent poly(o-anisidine) (POA) coatings have been successfully electrodeposited onto copper (Cu) substrates from the aqueous bath containing sodium oxalate and o-anisidine by using cyclic voltammetry (CV). CV, UV visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements were used to characterise these coatings, which indicates that the aqueous sodium oxalate solution is a suitable medium for the formation and deposition of POA onto Cu substrates. It is observed that the electrodeposition of POA coatings takes place after the passivation of the Cu substrate via formation of copper oxalate (CuC₂O₄.H₂O) layer, which is confirmed by XRD measurement. The optical absorption spectroscopy study reveals the formation of the mixed phase of pernigraniline base (PB) and emeraldine salt (ES) forms of POA. The surface morphology of the coating is uniform, compact and featureless as revealed by SEM imaging.