PEO Layer Research Articles

PEO layers obtained from mixed aluminate–phosphate baths on Ti–6Al–4V: Dry sliding behaviour and influence of a PTFE topcoat

Abstract The present study focuses on the influence of PEO treatments (performed in the AC regime using mixed aluminate–phosphate baths) on the tribological behaviour of Ti–6Al–4V, dry sliding against EN100Cr6 steel. Three different sets of coatings were produced: (set 1) in an aluminate-rich electrolyte; (set 2) in a phosphate-rich electrolyte; and (set 3) identical to set 2, but with the addition of a spray-deposited PTFE topcoat. The topography, microstructure, phase constitution and surface microhardness of each set were characterized and dry sliding tests were carried out in the load range 5–120 N using a block-on-ring tribometer. For each set, a transition load which corresponds to the end of coating life has been identified. The highest transition loads were observed for coatings produced using the aluminate-rich electrolyte (set 1). Intermediate values of transition load were measured for duplex PTFE/PEO coatings (set 3). Single-layer PEO coatings produced in the phosphate-rich electrolyte (set 2) showed the lowest values of transition load, due to the low coating thickness and poor uniformity. The deposition of the PTFE topcoat proved to be beneficial in terms of both friction and wear resistance, particularly in an intermediate (30–50 N) load range.

플라즈마 전해 산화 코팅에 있어서 알루미늄 합금 모재 성분의 물리적, 결정학적 영향 II. PEO 층의 결정상 분석

Physical properties of Plasma electrolytic oxidized 8 different kinds of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was Na₂SiO₃ and NaOH and some alkali earthen metal salts system solution. η-alumina, as well as γ-alumina, was main crystal phase, which were ever reported. Also, Al 4.95 Si 1.05 O 9.52 was found only in this research. So we can conclude that the process conditions of PEO apparatus and composition and concentration of its electrolyte affects crystal structure and physical properties of PEO layers much more than the compositions of Al alloy.

A new method for achieving nanoscale reinforcement of biaxially oriented polypropylene film

Nanolayers of poly(ethylene oxide) (PEO) produced by layer-multiplying coextrusion crystallize as single, high aspect ratio lamellae that resemble large single crystals. The confined crystallization habit imparts two orders of magnitude reduction in the gas permeability. We now demonstrate how the highly oriented lamellar nanolayers can be obtained with biaxial stretching. For this purpose, we chose biaxially oriented polypropylene (BOPP) film for modification and incorporated PEO nanolayers under conditions that mimicked the typical fabrication process. Sheet that contained a center core with 33 alternating layers of polypropylene (PP) and PEO was coextruded and subsequently biaxially oriented at 145°C. Biaxial stretching reduced the PEO layer thickness from the spherulitic microscale to nanolayers of highly oriented PEO single lamellae. The nanolayers improved the oxygen barrier by an order of magnitude without sacrificing the high clarity and good tear resistance of BOPP film.

Nisin adsorption to polyethylene oxide layers and its resistance to elution in the presence of fibrinogen

The adsorption and elution of the antimicrobial peptide nisin at silanized silica surfaces coated to present pendant polyethylene oxide chains was detected in situ by zeta potential measurements. Silica microspheres were treated with trichlorovinylsilane to introduce hydrophobic vinyl groups, followed by self assembly of the polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) triblock surfactant Pluronic® F108, or an F108 derivative with nitrilotriacetic acid end groups. Triblock-coated microspheres were γ-irradiated to covalently stabilize the PPO-surface association. PEO layer stability was evaluated by triblock resistance to elution by SDS, and layer uniformity was evaluated by fibrinogen repulsion. Introduction of nisin to uncoated or triblock-coated microspheres produced a significant positive change in surface charge (zeta potential) as a result of adsorption of the cationic peptide. In sequential adsorption experiments, the introduction of fibrinogen to nisin-loaded triblock layers caused a decrease in zeta potential that was consistent with partial elution of nisin and/or preferential location of fibrinogen at the interface. This change was substantially more pronounced for uncoated than triblock-coated silica, indicating that the PEO layer offers enhanced resistance to nisin elution.

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

The performance of polymer light emitting devices (PLEDs) based on polyvinyl carbazole (PVK) is improved by introducing a nanoscale interfacial thin layer, made of poly(ethylene oxide) (PEO), between the calcium cathode and the PVK emissive layer. It is believed that the PEO layer plays a key role in enhancing the device performance. In comparison to the device with Ca/Al as the cathode, the performance of the PLED with PEO/Ca/Al cathode, including the driving voltage, luminance efficiency is significantly improved. These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

Abstract The performance of polymer light emitting devices (PLEDs) based on polyvinyl carbazole (PVK) is improved by introducing a nanoscale interfacial thin layer, made of poly(ethylene oxide) (PEO), between the calcium cathode and the PVK emissive layer. It is believed that the PEO layer plays a key role in enhancing the device performance. In comparison to the device with Ca/Al as the cathode, the performance of the PLED with PEO/Ca/Al cathode, including the driving voltage, luminance efficiency is significantly improved. These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.

Structure and Phase Behavior of the Poly(ethylene oxide)−Thiourea Complex Prepared by Electrospinning

Electrospinning was used for the first time to prepare nanofibers of the host/guest complex between poly(ethylene oxide) (PEO) and thiourea. It is shown by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) that the stoichiometry of the complex is (EO)(12)-(thiourea)(8), settling a series of conflicting values in literature reports. The complex crystallizes in a monoclinic unit cell with a = 9.15 A, b = 18.88 A, c = 8.25 A, and beta = 92.35 degrees. On the basis of WAXD, infrared spectroscopy, and polarized Raman scattering measurements, it is proposed that the complex adopts a layered structure in which alternating PEO and thiourea layers are stabilized by intermolecular hydrogen bonds. This structure is highly reminiscent of that of the beta complex between PEO and urea. A phase diagram was determined and shows that the complex melts incongruently at 110 degrees C to form a peritectic liquid and crystals of pure thiourea. The nanofibers of the PEO-thiourea present a very large molecular orientation with a <P(2)(cos phi)>(c) value of 0.76, among the largest reported for electrospun materials.

Poly(ethylene oxide) Crystal Orientation Change under 1D Nanoscale Confinement using Polystyrene-block-poly(ethylene oxide) Copolymers: Confined Dimension and Reduced Tethering Density Effects

In this study, we systematically investigated the effects of confined dimension (the thickness of PEO layer) and reduced tethering density (σPEO, defined by σπRg2, where σ is the tethered chain density and Rg is the radius of gyration of the tethered PEO chain in its end-free state in the melt) on the PEO crystal orientation change within a 1D nanoscale confinement. We realized this confinement by utilizing two symmetric polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer single crystals grown at different crystallization temperatures (Tx) in dilute solution via the self-seeding technique. After these single crystals were collected as mats, the thicknesses of both the PEO single crystal (dPEO) and PS glassy layer were measured using small-angle X-ray scattering (SAXS) coupled to the 1D correlation function. Because TgPS is higher than TmPEO in those PS-b-PEO single crystal mats, 1D confinements having different dPEO and σPEO values can be prepared by changing Tx values. The PEO block sin...

End Terminal, Poly(ethylene oxide) Graft Layers: Surface Forces and Protein Adsorption

Covalently grafted poly(ethylene oxide) coatings have been widely studied for use in biomedical applications, particularly for the reduction of protein and other biomolecule adsorption. However, many of these studies have not characterized the hydrated structure of the coatings. This new study uses a combination of silica colloid probe interaction force measurements using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) in order to determine the grafting density and hydrated layer structure of monomethoxy poly(ethylene oxide) aldehyde layers, covalently grafted onto amine plasma polymer surfaces, and their interactions with silica surfaces. For high grafting densities, purely repulsive interactions were measured as expected for densely grafted polymer brushes. These interactions could be described by theoretical expectations for compression of one polymer brush layer. However, at lower grafting densities, attractive interactions were observed at larger separation distances, originating from bridging interactions due to adsorption of the PEO chains on the surface of the silica colloid probe. This is a new finding indicating that the coupled PEO molecules have sufficient conformational freedom to interact strongly with an adjacent surface or, for example, protein molecules for which there is an affinity. The attractive interactions could be removed by grafting an additional PEO layer onto the silica colloid probe. Protein adsorption measurements confirmed that at high grafting densities, the amount of adsorbed protein on the PEO grafted surfaces was greatly reduced, to the order of the detection limit for the XPS technique.

Modification of polypropylene and polypropylene/ fibrous cellulose composites by the addition of poly(ethylene oxide)

AbstractEffects of the addition of poly(ethylene oxide) (PEO) on the tensile properties of a polypropylene (PP)/fibrous cellulose (FC) composite were studied. PEO was incompatible with the PP matrix, and a PP/PEO blend showed a sea‐island morphology. However, the existence of the PEO phase hardly impaired the ductility of PP, leading to a strain constraint relaxation resulting from void formation in the phase. The tensile behavior of PP/PEO was little affected by the content (until 10 wt %) or molecular weight of PEO. The results suggested that the PEO phase was able to be deformed in a slit‐like shape and had no interaction with the PP matrix. Effects of PEO on the morphology and tensile and fracture behavior of the PP/FC composite with maleated polypropylene (MAPP) as a compatibilizer critically depended on the preparation method. In the case of the addition of PEO to PP/FC/MAPP, increases in the strain and fracture energy were observed in comparison with PP/FC. In the case of the addition of FC/PEO to PP/MAPP, although the obtained composite showed a lower Young's modulus and tensile strength in comparison with PP/FC, the strain and fracture energy were considerably increased by the existence of the PEO layer coating the FC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The role of hydrogen bonding in tethered polymer layers.

A molecular theory to study the properties of end-tethered polymer layers, in which the polymers have the ability to form hydrogen bonds with water, is presented. The approach combines the ideas of the single-chain mean-field theory to treat tethered layers with the approach of Dormidontova (Macromolecules, 2002, 35, 987.) to include hydrogen bonds. The generalization includes the consideration of position-dependent polymer-water and water-water hydrogen bonds. The theory is applied to model poly(ethylene oxide) (PEO), and the predictions are compared with equivalent polymer layers that do not form hydrogen bonds. It is found that increasing the temperature lowers the solubility of the PEO and results in a collapse of the layer at high enough temperatures. The properties of the layer and their temperature dependence are shown to be the result of the coupling between the conformational entropy of the chains, the ability of the polymer to form hydrogen bonds, and the intermolecular interactions. The structural and thermodynamic properties of the PEO layers, such as the lateral pressure-area isotherms and polymer chemical potentials, are studied as a function of temperature and type of tethering surface. The possibility of phase separation of the PEO layer at high enough temperature is predicted due to the reduced solubility induced by breaking of polymer-water hydrogen bonds. A discussion of the advantages and limitations of the theory, together with how to apply the approach to different hydrogen-bonding polymers, is presented.

Characterization of the stable and metastable poly(ethylene oxide)–urea complexes in electrospun fibers

AbstractSolution electrospinning was used for the first time to prepare nanofibers of the stable (α) and metastable (β) complexes between poly(ethylene oxide) (PEO) and urea. Both types of fibers were highly crystalline and presented a large level of molecular orientation. Detailed characterization of the ill‐studied β complex was performed using wide angle X‐ray diffraction (WAXD), infrared spectroscopy, and differential scanning calorimetry (DSC). Results reveal that it possesses a 3:2 PEO:urea stoichiometry and suggest that it belongs to the orthorhombic system with a = 1.907 nm, b = 0.862 nm, and c = 0.773 nm. The PEO chains are oriented along the fiber axis and present a conformation significantly affected by strong hydrogen bonding with urea when compared with the pure polymer and the stable complex. A layered structure model is suggested for the metastable complex, in which the urea molecules would be arranged into a ribbon‐like structure intercalated between two PEO layers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1903–1913, 2008

Internal Structure of a Thin Film of Mixed Polymeric Micelles on a Solid/Liquid Interface

The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-poly(ethylene oxide), PAETB 49- b-PEO 212 and poly(4-(2-sodium carboxylate-ethylthio)-butylene)- block-poly(ethylene oxide), PCETB 47- b-PEO 212 on solid/liquid interfaces has been studied with light, X-ray, and neutron reflectometry. The structure of the adsorbed layer can be described with a two-layer model consisting of an inner layer formed by the coacervate of the polyelectrolyte blocks PAETB 49 and PCETB 47 ( approximately 1 nm) and an outer layer of PEO 212 blocks ( approximately 6 nm). The micelles unfold upon adsorption forming a rather homogeneous flat layer that exposes its polyethylene oxide chains into the solution, thus rendering the surface antifouling after modification with the micelles.

A Small-Angle Neutron Scattering Study of Adsorbed Polymer Structure in Concentrated Colloidal Dispersions

Poly(ethylene oxide) (PEO) adsorption on colloidal silica particles was studied by small-angle neutron scattering under the core-contrast-matching condition. The volume fraction profile of the adsorbed layer was derived by modeling the average layer scattering term. It was found that, with increasing colloid concentration, the adsorbed PEO layers collapse due to the repulsions between adsorbed layers on neighboring particles. At the same time, the correlation length in the adsorbed layer obtained by fitting the layer fluctuation scattering term was found to decrease, indicating that denser polymer layers are formed. These two observations are self-consistent.

Shear Behavior of Adsorbed Poly(ethylene Oxide) Layers in Aqueous Media

We use a surface force balance to study shear interactions between adsorbed poly(ethylene oxide) layers (Mw = 150 000 or 170 000) adsorbed onto mica in 0.1 M KNO3 aqueous solution. The shear forces increase with increasing compression of the layers or with increasing shear rates (at a constant compression), though at high compressions or shear rates the shear stress σs appears to saturate. This behavior is attributed to frictional effects that are dominated by viscous dissipation (and possible weak monomer−monomer complexing) between the mutually sliding layers at low compressions or shear rates, and by a substrate-slip mechanism at the highest compressions and shear rates. The shear behavior of adsorbed PEO layers in aqueous electrolyte at the higher compressions or shear rates can be well understood in terms of the attachment mechanism of PEO segments, via ion ligands to the charged substrate (as elucidated earlier, J. Am. Chem. Soc. 2005, 127, 1104).

Protein-Resistant Poly(ethylene oxide)-Grafted Surfaces: Chain Density-Dependent Multiple Mechanisms of Action

A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, protein adsorption kinetics, and ultimate protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of protein resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of protein resistance at chain densities greater than the critical value.

A simple swelling and anchoring method for preparing dense and stable poly(ethylene oxide) layers on polystyrene surfaces

In order to obtain dense and stable poly(ethylene oxide) (PEO) layers for reducing protein adsorption, polystyrene (PS) plates were first soaked in chloroform/methanol mixed organic solvent to swell the polymer. The swelled PS plates were then immersed into Pluronic F127 (amphiphilic block copolymer) aqueous solution, Pluronic F127 molecules were adsorbed favorably on the swelled PS surfaces. After evaporation of organic solvent, the adsorbed Pluronic F127 molecules were trapped and anchored permanently on the PS substrates. The dense and stable PEO layers anchored on the PS surfaces can effectively inhibit protein adsorption.

Electrospinning and Characterization of the Stable and “Metastable” Self-Assembled Poly(ethylene oxide)-Urea Complexes

ABSTRACTSolution electrospinning was used to prepare fibers of both the stable – trigonal α and “metastable” – orthorhombic β complexes between poly(ethylene oxide) (PEO) and urea. The 300-800 nm fibers were highly crystalline and both types presented a relatively large level of molecular orientation. Characterization of the poorly-studied β complex was performed using wide-angle X-ray diffraction, infrared spectroscopy, optical microscopy and differential scanning calorimetry. It was shown that β complex possesses a 3:2 PEO:urea stoichiometry, in contrast with a previously suggested 1:1 molar ratio, and that the α inclusion complex keeps the 4:9 molar ratio as when prepared by the conventional co-crystallization method. A new structural model was suggested for the β complex, in which the unit cell would contain 12 PEO repeat units (4 chains in the ab plane with 3 repeat units along the c axis) and 8 urea molecules arranged in a ribbon-like structure and intercalated between the two PEO layers. This layer-structured β complex is quite different from the usual channel-like α inclusion complex and results in different phase transitional properties.

Analysis of Multilayer Structure of Amphiphilic Di-block Copolymer by X-ray Reflectivity

The structure of Langmuir-Blodgett (LB) membranes of liquid crystal amphiphilic di-block copolymer, poly(ethylene oxide)-b-poly{11-[4-(4-butylphenylazo) phenoxy]-undecyl methacrylate, (PEO-b-PMA(Az)) was investigated by X-ray reflectivity (XR). XR results indicated that the structure of LB membranes below 6 layers was formed by the head to head type bilayer structure consisting of the extended hydrophilic PEO and the compressed hydrophobic PMA(Az) layers. In the case of 10 layers, the another type of bilayers consisting of the interdigitate PMA(Az) structure corresponding to the smectic C phase in the bulk state and the collapsed PEO layer were lapped on the bilayer structure of 6 layers. The structural transition from the head to head type bilayer to the interdigitate bilayer occurred around 6 to 10 layers.

Enhancing the Photovoltage of Polymer Solar Cells by Using a Modified Cathode

A method to increase the open-circuit voltage (Voc) up to 200 mV and the power conversion efficiency (PCE) by 50%, by using a thin layer of poly(ethylene oxide) (PEO) to modify the cathode in polymer solar cells, was reported. An enhanced photocurrent of polymer solar cells by bending a small amount of PEO and LiCF3SO3 into the active layer was also demonstrated. The results show that the value of open-circuit voltage increases in all diodes with PEO by 150 to 200 mV while the fill factor (FF) increases with a decrease of the thickness of PEO. The thickness of the PEO layers on Si wafers measured by using ellipsometry shows that the thickness are 3.8 nm for 1000 rmp, 2.1 nm for 3000 rmp, and 1.4 nm for 5000 rmp. The quantitative similarity of the J-V characteristics in the dark between the diodes containing PEO and LiF shows that PEO has an analogous function in the device as LiF.