Ion beam induced crystal-edge nanoclusters at the origin of poly(ethylene glycol) film stabilization

PEG films stabilized by noble gas ion beam irradiation showed characteristic clustering at the crystal edges. These structures appear in determined ion beam conditions after exposure to Ar and Kr ions. Atomic force microscopy exploration indicates that, rather than presenting drastic topographic features, the nanostructures show radically different elastic properties. Within the concerned set of ion beam conditions, the surface properties are observed to vary according to the absorbed energy as suggested by X-ray photoelectron spectroscopy and contact angle measurements. These analyses predict that Ar irradiation in the 500-600 V extraction potential range is an appropriate condition for PEG stabilization.     

Poly(ethylene glycol) and phospholipid packing in the structure of reverse micelles

The influence of water substitution by a substance with a different polarity on the structure of phospholipid monolayer interface in water-in-oil microemulsion has been studied by the Fourier-transform pulsed-gradient spin-echo (FT PGSE)¹H nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spin-label methods. For this purpose the soybean phosphatidylcholine-based microemulsion and water soluble poly(ethylene glycol) with molecular weight 400 (PEG400) were used. Self-diffusion coefficients of all microemulsion components obtained by the FT PGSE NMR technique provided information about both the size of reverse micelles and distribution of components between different microemulsion compartments. The maximum hyperfine splitting, 2A _max, in the ESR spectra was used to characterize the degree of the phospholipid hydrocarbon chain mobility. It was shown that PEG400 alters significantly the size of the reverse micelles and the motion of the labeled segments of the lipid tails. A mechanism of PEG400 acting in solution of the phospholipid-based reverse micelles on the basis of the rough decrease of the micelle core polarity was suggested.     

Effect of shape,height,and interparticle spacing of Au nanoparticles on the sensing performance of Au nanoparticle array

The effect of shape,height,and interparticle spacing of Au nanoparticles(NPs) on the sensing performance of Au NP array is systematically investigated. Lengthening the major axis of elliptical NPs with the minor axis kept constant will cause the redshift of the local surface plasmon(LSP) resonance mode,enhance the sensitivity,and widen the resonance peaks. Larger height corresponds to smaller LSP resonance wavelength and narrower resonance peak. With each NP size unchanged,larger interparticle spacing corresponds to larger resonance wavelength and smaller full-width at half-maximum(FWHM) . Moreover,duty cycle is important for sensitivity,which is largest when the duty cycle is 0.4.     

Effect of poly (ethylene glycol) coating on the magnetic and thermal properties of biocompatible magnetic liquids

The aim of this study was to investigate the influence of poly(ethylene glycol) surface-active coating on the magnetic and thermal properties of biocompatible magnetic liquids. The data were analyzed using the high-temperature approximation model taking into account polydispersity of a system. Heating ability of the PEG-stabilized magnetic fluids was determined by the calorimetric measurement of specific absorption rate (SAR) at a frequency of 750 kHz and a magnetic field of 0-2 kA/m. MF-Oleate/PEG heating properties were found to be comparable to the ones of MF-Oleate. The PEG shell thus does not seem to effect the thermal characteristics and SAR values and might make the magnetic fluid useful for application in hyperthermia treatment.     

Covalent attachment of poly(ethylene glycol) on multi-walled carbon nanotubes

A new 'graft-onto' method to attach poly(ethylene glycol) (PEG) onto multi-walled carbon nanotubes (MWNTs) has been developed. The method is based on the coupling reaction of radicals formed at the chain end of PEG onto the surface of MWNTs. The polymeric radicals are generated by atom (halogen) transfer reaction between chloroacetyl-terminated PEG and transition metal catalysts. The method allows direct covalent attachment of PEG to pristine MWNTs without pretreatment that could alter their original structure. The resulting PEG-grafted MWNTs showed improved dispersion stability in isopropanol and methanol.     

Reduction of Se(VI) to Se(-II) by zerovalent iron nanoparticle suspensions

The reaction of selenate (Se(VI)) with zerovalent iron nanoparticles (nano Fe⁰) was studied using both conventional batch equilibrium and X-ray spectroscopic techniques. Nano Fe⁰ has a high uptake capacity for removal of dissolved Se(VI) reaching concentrations as high as 0.10 Se:Fe molar ratio in the solid product mixture. Kinetic studies of the Se(VI) uptake reaction in batch experiments showed an initial reaction rate (0–30 min) of 0.0364 min^?1 which was four times greater than conventional Fe⁰ powder. Analysis of the oxidation state of Se in the solid products by X-ray absorption near edge structure (XANES) spectroscopy showed evidence for the reduction of Se(VI) to insoluble selenide (Se(-II)) species. Structural analysis of the product by extended X-ray absorption fine structure (EXAFS) spectroscopy suggested that Se(-II) was associated with nano Fe⁰ oxidation products as a poorly ordered iron selenide (FeSe) compound. The fitted first shell Se–Fe interatomic distance of 2.402 (±0.004) Å matched closely with previous studies of the products of Se(IV)-treated Fe(II)-clays and zero-valent iron/iron carbide (Fe/Fe₃C). The poorly ordered FeSe product was associated with Fe⁰ corrosion product phases such as crystalline magnetite (Fe₃O₄) and Fe(III) oxyhydroxide. The results of this investigation suggest that nano Fe⁰ is a strong reducing agent capable of efficient reduction of soluble Se oxyanions to insoluble Se(-II).     

Light scattering and phase behavior of lysozyme-poly(ethylene glycol) mixtures

Measurements of liquid-liquid phase transition temperatures (cloud points) of mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG) show that the addition of low molecular weight PEG stabilizes the mixture whereas high molecular weight PEG was destabilizing. We demonstrate that this behavior is inconsistent with an entropic lysozyme-PEG depletion interaction and suggest that an energetic lysozyme-PEG attraction is responsible. In order to independently characterize the lysozyme-PEG interactions, light scattering experiments on the same mixtures were performed to measure second and third virial coefficients. These measurements indicate that PEG induces repulsion between lysozyme molecules, contrary to the depletion prediction. Furthermore, it is shown that third virial terms must be included in the mixture's free energy in order to qualitatively capture our data.     

The thermal conductivity of alumina nanofluids in water, ethylene glycol, and ethylene glycol + water mixtures

We present new data on the thermal conductivity of nanofluids consisting of alumina nanoparticles dispersed in water, ethylene glycol, and ethylene glycol + water mixtures. We also demonstrate that our previously published model is able to describe the temperature, particle size, and particle volume fraction dependence of these nanofluids without any adjustable parameters, irrespective of the base fluid used (water, ethylene glycol, or water + ethylene glycol mixtures). Furthermore, we demonstrate how the model may be used to check the consistency of literature data on all alumina nanofluids.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.     

Growth, structure and oxidation of ordered silicon layers on nickel (001)

Thin silicon films deposited in ultra-high vacuum on Ni(001) have been studied, as a function of annealing and/or O₂ exposure, using Auger spectroscopy and low energy electron diffraction. Annealing at temperatures as low as 200 ° C causes rapid intermixing, with only about one monolayer of Si (θ ≈ 1) remaining in a disordered surface layer. Annealing at successively higher temperatures causes further intermixing and the appearance of a c(2 × 2) ordered overlayer (θ = 0.5). The rate of O chemisorption and the structure of the oxide are found to depend on the structure of the adsorbed Si layer. For the c(2 × 2) layer, O₂ exposure leads to the rapid formation of multiple Si---O bonds at all surface Si sites, as in the case of bulk Ni₃Si. This effect is less pronounced (and the saturation O coverage lower) for a surface having a somewhat higher Si coverage but in the form of a disordered layer. The results are interpreted in terms of the involvement of underlayer Ni atoms in promoting O₂ dissociation.     

Effect of temperature on the intrinsic viscosity of poly(ethylene glycol) in water/dimethyl sulfoxide solutions

In this work, the intrinsic viscosities of poly(ethylene glycol) with molar mass of 20 kg mol^− 1 were measured in water/dimethyl sulfoxide solutions from (298.15 to 318.15) K. The expansion factors of the polymer chains were calculated from the intrinsic viscosity data. The expansion factor were decreased by increasing temperature; therefore the chain of PEG shrinks and the end-to-end distance become smaller by increasing temperature. Perhaps the interactions of segment-segment are favored toward segment-solvent by increasing temperature; therefore the hydrodynamic volumes of the polymer coils become smaller by increasing temperature. The thermodynamic parameters (entropy of dilution parameter, the heat of dilution parameter, theta temperature and polymer-solvent interaction parameter) were derived by the temperature dependence of the polymer chain expansion factor. The thermodynamic parameters indicate that the interactions of segment-segment were increased by increasing temperature.     

Ultrasound responsive block copolymer micelle of poly(ethylene glycol)–poly(propylene glycol) obtained through click reaction

The well-defined amphiphilic poly(ethylene glycol)-block-poly(propylene glycol) copolymer containing 1, 2, 3-triazole moiety and multiple ester bonds (PEG-click-PPG) was prepared by click reaction strategy. The PEG-click-PPG copolymer can self-assemble into spherical micelles in aqueous solution. It is found that high intensity focused ultrasound (HIFU) can open the copolymer PEG-click-PPG micelles and trigger the release of the payload in the micelle. The multiple ester bonds introduced in the junction point of the copolymer chain through click reactions were cleaved under HIFU, and leads to the disruption of the copolymer micelle and fast release of loaded cargo. The click reaction provides a convenient way to construct ultrasound responsive copolymer micelles with weak bonds.     

Upon a magnetic composite preparation based on magnetite and poly(succinimide)-b-poly(ethylene glycol) shell

Taking into account that magnetic particles with suitable surface characteristics have a high potential for the use in a lot of in vitro and in vivo applications, in the study is presented the in situ preparation of a core-shell magnetic composite based on the magnetite core and the shell composed from the poly(succinimide)-b-poly(ethylene glycol) copolymer. The average particle size of the synthesized magnetic microspheres is in the range of 6.5-8.8 μm with a magnetite content of around 11%. The saturation magnetization of the microspheres was found 26.8 emu/g, the magnetic microspheres being characterized by superparamagnetic properties. The particles have combined properties of high magnetic saturation and biocompatibility and interactive functions at the surface through the block copolymer shell. The surface of the magnetic particles has also the possibility for further functionalization or the attachment of various bioactive molecules after the hydrolysis of the succinimide cycle and the resulting carboxylic group.     

Self-assembly of silanated poly(ethylene glycol) on silicon and glass surfaces for improved haemocompatibility

Surface immobilization of poly(ethylene glycol) (PEG) is an effective method to produce a material surface with protein repulsive property. This property could be made permanent by using covalent grafting of the PEG molecules onto material surfaces. In this study, self-assembled monolayers (SAMs) of PEG on silicon-containing materials (silicon chip and glassplate) were obtained through a one-step coating procedure of one kind of silanated PEG molecules made through the reaction between monomethoxy PEG and 3-isocyanatopropyltriethoxysilane. Atomic force microscopy (AFM) and water static contact angle measurement were employed to investigate the surface topography and wettability of the PEGylated material surfaces. The changes in the topography and the water contact angle of the surfaces with time of incubation in PBS solution were also measured. The results revealed that stable and uniform self-assembled monolayers of PEG could be formed on silicon or glass surfaces by simply soaking the substrates in the solution of silanated PEGs. The covalent coupling of PEGs to the substrates was also confirmed. In order to evaluate the stability of the SAMs, blood compatibility of the modified glassplate surface was evaluated by measuring full blood activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT), as well as by scanning electron microscopy (SEM) analysis of the appearance of adherence and denaturation of blood platelets onto the glassplate. The silanated PEGs were shown to have good effect on the protein-repulsion as well as haemocompatibility of the substrates.     

Polymer electrolytes based on copolymer of poly(ethylene glycol) dimethacrylate and imidazolium ionic liquid

Polymer electrolytes based on the copolymer of N-vinylimidazolium tetrafluoroborate (VyImBF₄) and poly(ethylene glycol) dimethacrylate (PEGDMA) have been prepared. Ethylene carbonate (EC) and LiClO₄ are added to form gel polymer electrolytes. The chemical structure of the samples and the interactions between the various constituents are studied by FT-IR. TGA results show that these polymer electrolytes have acceptable thermal stability, are stable up to 155 °C. Measurements of conductivity are carried out as a function of temperature, VyImBF₄ content in poly(VyImBF₄-co-PEGDMA), and the concentration of EC and LiClO₄. The conductivity increases with PEGDMA and EC content. The highest conductivity is obtained with a value of 2.90 × 10^? 6 S cm^? 1 at room temperature for VP1/EC(25 wt.%)–LiClO₄ system, corresponding to the LiClO₄ concentration of 0.70 mol kg^? 1 polymer.     

Dynamics of concentrated colloidal suspensions during drying --aging,rejuvenation and overaging

We report on the slow dynamics of concentrated colloidal suspensions during drying and rewetting under conditions of reversible concentration changes without coalescence or aggregation. We used multispeckle diffusing-wave spectroscopy to monitor the slow dynamics of particles. We found that the relaxation of the suspensions exhibits successively slowing-down, acceleration and a stationary regime during drying at constant rates. Under rewetting conditions, we observed slowing-down and a stationary regime. The characteristic time of the stationary regime is inversely proportional to the rate of concentration change and identical for both drying and rewetting. We explain these regimes as aging (overaging), rejuvenation and plastic flow of the suspensions induced by a deviatoric stress (a combination of compressive and elongational stresses) which is induced by the uniaxial compressive strain generated by evaporation.Received: 3 June 2004, Published online: 3 August 2004PACS: 82.70.Dd Colloids - 47.55.Mh Flows through porous media - 42.25.Dd Wave propagation in random media     

The Effect of Hydrophilic Bentonite Nanoclay on the Thermogelation Properties of Poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) Triblock Copolymer Aqueous Solutions

The effect of hydrophilic bentonite addition on the thermogelation properties of aqueous solutions of poly(N-isopropylacrylamide)–poly(ethylene glycol)–poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) triblock copolymers of various compositions and molecular weights was investigated. Dynamic rheometry and differential scanning calorimetry (DSC) measurements showed that increasing concentrations of clay added to 20 wt.% polymer aqueous solutions caused a decrease of the temperature at which the viscosity starts increasing, while the temperature corresponding to the maximum endothermic effect due to the PNIPAM chain dehydration remained practically unchanged. The storage modulus, G′, increased with clay concentration for shorter PNIPAM chain triblock copolymers, while an opposite situation occurred in the case of the block copolymer with the longest PNIPAM block. For bentonite concentrations above 1 wt.%, G′ was larger than the viscous modulus, G″, at temperatures higher than the phase separation temperature, indicating a predominantly elastic character of the resulting composite hydrogels. These findings were explained through the presence of polymer–clay interactions occurring mainly through the PEG blocks.     

Tetragonal structure of thin nickel films on Cu(001)

The crystallographic structure of thin Ni films deposited on Cu(001) has been studied using Surface Extended X-ray Absorption Fine Structure (SEXAFS). Taking advantage of the linear polarization of the synchrotron radiation, we have shown that Ni adopts the Cu lattice parameter parallel to the interface. This lateral expansion induces a longitudinal compression of the unit cell, leading to a face centered tetragonal structure of the Ni films from 3 to 10 monolayers. The temperature dependence of the EXAFS oscillations has allowed to measure strain inside the Ni layers. Received 22 December 1998     

A model of ethylene and acetylene adsorption on the (111) surfaces of platinum and nickel

Despite the application of a variety of surface sensitive techniques to the adsorption of simple hydrocarbons on well characterized metallic surfaces, no consistent picture has appeared. We review briefly the published spectroscopic results of ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) which probe, respectively, the electronic and vibrational structure of the surface-molecular complex, and we consider appropriate free molecular analogues, not only in their ground state but also in their first excited states. A simplified approach to determine the chemisorption geometry from UPS level shifts and EELS is presented. The technique allows an isolation of distortion induced shifts from the total relaxation shift, and we find that the true relaxation shift is rather constant, approximately 2.1 eV for the cases considered. These shifts can then be used to estimate the distance of the molecule to the surface. We concentrate primarily on four systems, C₂H₂ and C₂H₄ on Ni(111) and Pt(111), adsorbed at low temperature (below the onset of dissociation). Depending on the metal, the hydrocarbon can adsorb in a di-σ arrangement or with a distortion resembling the lowest energy configuration of the first excited state of the free molecule. We also consider briefly C₂H₄ on Ag and Cu in which no distortion occurs. The distortions that resemble the first excited states might occur as a consequence of donation of bonding (backbonding) electrons from (to) the normally filled π (empty π¹) to (from) the empty (filled) d-band states of the metal. The net effect on the hydrocarbon to partially empty the π level and fill the π¹ level, is analogous to a low excitation of the free molecule, π → π¹. For C₂H₄ (planar in the ground state), the lowest excitation is the triplet T-state (3–4 eV) of minimal energy for a 90° twisted configuration with a lengthened C-C bond. Acetylene is a linear molecule in the ground state, but cis- or trans-bent for the triplet excitations, ~a (5.2 eV) or ~b (6.0 eV), respectively. Chemisorbed geometries derived from these configurations seem possible for C₂H₄ on Ni(111) and C₂H₂ on Pt(111), while interchanging the adsorbates and substrates gives di-σ bonding, (sp³ hybridization), as proposed previously in the literature. For C₂H₄ on Ni(111), two of the hydrogens are twisted into the surface which leads to a softening of the CH vibrational frequency. For the four systems considered, the data are consistent with the C-C bond essentially parallel to the surface, but tilted orientations are not ruled out. While the models are clearly oversimplified, they suggest an interesting point of departure for likely chemisorption geometries. Also, some intriguing correspondences to the (presumed) location of the normally empty π¹ level and the d-band are noted.     

Polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) with crosslinked poly(ethylene glycol) for lithium batteries

The combination of a poly(ethylene glycol) (PEG) network and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) copolymer chains is one of the most efficient means for modifying PVDF-HFP gel electrolytes. Previous preparations tend to introduce contamination into the polymer gel electrolyte because of irradiation, high temperature or the initiator needed for crosslinking which might result in the electrochemical degradation. In order to overcome the above disadvantages, a new method has been developed to successfully prepare the semi-interpenetrating polymer networks of PVDF-HFP based electrolytes with crosslinked diepoxy polyethylene glycol (DIEPEG). In this process, impurities are avoided because of a moderate reaction temperature at 50 °C and poly(ethylenimine) (PEI) as the crosslinking agent. Microporous films with various compositions are prepared and characterized. Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes have been investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results show that the blend polymer electrolyte with PVDF-HFP/PEI + DIEPEG (60:40 w/w) has an ionic conductivity of 2.3 mS cm^? 1 at room temperature in the presence of 1 M LiPF₆ in EC and DMC (1:1 w/w). All the blend electrolytes are electrochemically stable up to 4.8 V versus Li/Li⁺. The results reveal that this new method may be very promising for improving PVDF-HFP based electrolytes.