Pu Surface Research Articles

Surface modification on polyurethanes by using bioactive carboxymethylated fungal glucan from Poria cocos

In this work, a water-insoluble β- d-glucan (PCSG), isolated from Poria cocos, was carboxymethylated to create a water-soluble derivative named as CP. After free amino groups have been introduced, CP was covalently immobilized onto PU surface. The hydrophilicity and the concentration of carboxyl group on the modified PU surface were determined. The fibrinogen and albumin adsorption to the surface, in vitro blood compatibility, and antibacterial activity of the surface against Pseudomonas aeruginosa were evaluated. The water contact angle measurement indicated that the hydrophilicity of PU surface increased after modification. The fibrinogen adsorption of the modified PU surface decreased 51.5%, compared with control PU. CP immobilization could prolong the blood coagulation time was suggested by APTT experiment. Antibacterial activity experiments indicated that CP modified surface obviously suppressed the growth of P. aeruginosa. Thereby, CP immobilization improves blood compatibility of PU surface and introduces special antibacterial bioactivity.

Protein resistance of polyurethane with hydrophilic and hydrophobic soft segments

AbstractPolyurethane (PU) containing poly(propylene glycol) (PPG) or poly(tetramethylene oxide) (PTMG) soft segments have been prepared by two‐step condensation polymerization. The former (PPG‐PU) with a lower critical solution temperature (LCST) at ∼21 °C can change from hydrophilic to hydrophobic, whereas the latter (PTMG‐PU) is hydrophobic at a temperature above 0 °C. The adsorption of fibrinogen, bovine serum albumin, or lysozyme on such a PU surface in aqueous solution has been investigated by use of quartz crystal microbalance with dissipation (QCM‐D) and surface plasmon resonance (SPR) in real time. PPG‐PU surface exhibits protein resistance at a temperature below the LCST of PPG, but it significantly adsorbs proteins at a temperature above the LCST. On the other hand, the hydrophobic PTMG‐PU surface adsorb the proteins at any temperatures investigated, in contrast with the hydrated poly(ethylene glycol) exhibiting excellent protein resistance. The hydration and dehydration of the polymers at different temperatures were confirmed by Raman spectroscopy. Our study demonstrates that the protein resistance of polymers is determined by their hydration. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1987–1993, 2010

In vivo modulation of foreign body response on polyurethane by surface entrapment technique

Implanted polymeric materials, such as medical devices, provoke the body to initiate an inflammatory reaction, known as the foreign body response (FBR), which causes several complications. In this study, polyurethane (Tecoflex®, PU) surface modified with the nonionic surfactant Tween80® (PU/T80) and the cell adhesive PLL-RGD peptide (PU/PLL-RGD) by a previously described entrapment technique were implanted in the peritoneal cavity of Wistar rats for 30 days. Implants were retrieved and examined for tissue reactivity and cellular adherence by various microscopic and analytical techniques. Surface-induced inflammatory response was assessed by real-time PCR based quantification of proinflammatory cytokine transcripts, namely, TNF-α and IL-1β, normalized to housekeeping gene GAPDH. Cellular adherence and their distribution profile were assessed by microscopic examination of H&E stained implant sections. It was observed that PU/PLL-RGD followed by the bare PU surface exhibited severe inflammatory and fibrotic response with an average mean thickness of 19 and 12 μm, respectively, in 30 days. In contrast, PU/T80 surface showed only a cellular monolayer of 2-3 μm in thickness, with a mild inflammatory response and no fibrotic encapsulation. The PU/PLL-RGD peptide-modified substrate promoted an enhanced rate of macrophage cell fusion to form foreign body giant cell (FBGCs), whereas FBGCs were rarely observed on Tween80®-modified substrate. The expression levels of proinflammatory cytokines (TNF-α and IL-1β) were upregulated on PU/PLL-RGD surface followed by bare PU, whereas the cytokine expressions were significantly suppressed on PU/T80 surface. Thus, our study highlights modulation of foreign body response on polyurethane surfaces through surface entrapment technique in the form of differential responses observed on PLL-RGD and Tween80® modified surfaces with the former effective in triggering tissue cell adhesion thereby fibrous encapsulation, while the later being mostly resistant to this phenomenon.

Prevention of polyurethane oxidative degradation with phenolic antioxidants covalently attached to the hard segments: Structure–function relationships

Oxidative degradation of the polyurethane elastomeric (PU) components greatly reduces the efficacy of PU-containing cardiovascular devices. Covalently appending the phenol-based antioxidant, 4-substituted 2,6-di-tert-butylphenol (DBP), to PU hard segments effectively reduced oxidative degradation of the PU in vivo and in vitro in prior studies by our group. In these experiments, we analyze the contribution of the tethering molecule to the antioxidant capabilities of the DBP-modified PU. Bromoalkylation chemistry was used to link DBP to the hard segment of the polyether PU, Tecothane, via our original linker (PU-DBP) or variants containing side chains with one (PU-C-DBP) or three (PU-3C-DBP) carbons. Two additional DBP variants were fabricated in which the DBP group was appended to the alkyl chain via an oxygen atom (PU-O-DBP) or an amide linkage in the middle of the tether (PU-NHCO-DBP). All DBP variant films and unmodified control films were subject to oxidative degradation via 15-day immersion in a solution of 20% H(2)O(2) + 0.1M CoCl(2). At the end of the oxidation protocol, films were analyzed for the presence of oxidation-related endpoints via scanning electron microscopy, contact angle measurements, and Fourier transformation infrared spectroscopy (FTIR). All DBP-containing variants resisted oxidation damage significantly better than the unmodified control PU. SEM analysis of oxidized PU-C-DBP and PU-O-DBP showed evidence of surface cracking, consistent with oxidative degradation of the PU surfaces. Similarly, there was a trend in increased ether crosslinking, a marker for oxidative degradation, in PU-C-DBP and PU-NHCO-DBP films. Consistent with these FTIR results, both PU-C-DBP and PU-NHCO-DBP had significant reductions in measured surface hydrophobicity as a result of oxidation. These data show for the first time that the choice of linker molecule significantly affects the efficiency of the linked phenolic antioxidant.

Surface structural conformations of fibrinogen polypeptides for improved biocompatibility

This work reports on how incorporation of silica nanocages into poly(urethane) copolymers (PU) affects conformational orientations of adsorbed fibrinogen and how different surfaces subsequently influenced HeLa cell attachment and proliferation. Incorporation of 2 wt% silica nanocages into poly(urethane) (PU4) substantially altered the surface topography of the films and some 50% of the surface was covered with the nanocages due to their preferential exposure. AFM studies revealed the deposition of a dense protein network on the soft polymeric domains of PU4 and much reduced fibrinogen adsorption on the hard nanocage domains. As on the bare SiO 2 control surface, fibrinogen molecules adsorbed on top of the hard nanocages mainly took the dominant trinodular structures in monomeric and dimeric forms. In addition, net positively charged long α chains were prone to being hidden beneath the D domains whilst γ chains predominantly remained exposed. Dynamic interfacial adsorption as probed by spectroscopic ellipsometry revealed fast changes in interfacial conformation induced by electrostatic interactions between different segments of fibrinogen and the surface, consistent with the AFM imaging. On the PU surfaces without nanocage incorporation (PUA), however, adsorbed fibrinogen molecules formed beads-like chain networks, consistent with the structure featured on the soft PU4 domains, showing very different effects of surface chemical nature. Monoclonal antibodies specific to the α and γ chains showed reduced α but increased γ chain binding at the silicon oxide control and PU4 surfaces, whilst on the PUA, C18 and amine surfaces (organic surface controls) the opposite binding trend was detected with α chain binding dominant, showing different fibrinogen conformations. Cell attachment studies revealed differences in cell attachment and proliferation, consistent with the different polypeptide conformations on the two types of surfaces, showing a strong preference to the extent of exposure of γ chains.

A pilot randomised controlled trial comparing reactive air and active alternating pressure mattresses in the prevention and treatment of pressure ulcers among medical ICU patients

Background Data on the prevention and treatment of pressure ulcers (PU's) among ICU patients is sparse. Objective To compare PU outcomes in medial ICU patients nursed on either a reactive mattress overlay (ROHO ®, ROHO Inc, Belleville, IL, USA) or an active alternating pressure mattress (NIMBUS ®3, ArjoHuntleigh, Luton Bedfordshire, UK). Design Pilot prospective single blind randomised controlled clinical trial. Intervention Two types of pressure redistributing mattress. Patients Two groups of eight patients. Methods Patients included in the study were those at high risk (Norton scale <8) or with a PU on admission. Results The two groups had similar patient characteristics. However, the NIMBUS 3 group presented with more ulcers per patient on admission (62.5%) and more severe ulcers (20% category 3) while four patients (50%) presented with a single superficial ulcer in the ROHO group. Healing The progress of the ulcers showed significant decreases in PU surface area ( p = 0.05), total PUSH tool score ( p = 0.01) in the NIMBUS 3 group compared to the ROHO group. In the NIMBUS 3 group 82% of the ulcers improved versus none in the ROHO group ( p = 0.002) and 18% remained stable versus 33%. None of the ulcers deteriorated in the NIMBUS 3 group versus 67% in the ROHO group ( p = 0.006). Full thickness wounds (Category 3) were present in 22% of the NIMBUS 3 group versus 0% of the ROHO group on admission and in 0% versus 66.7% ( p = 0.008) respectively at the end of the pilot study. Prevention Non-blanching erythema occurred equally in both arms at baseline; skin remained intact for the NIMBUS 3 group while 50% in the ROHO group worsened with superficial tissue loss. Conclusion This small pilot study suggests that ‘active’ alternating therapy is a useful adjunct in the care of highly vulnerable patients, while the outcomes may be less favourable when using ‘reactive’, constant low pressure devices.

A first principles study of the adsorption and dissociation of CO2 on the δ-Pu (111) surface

A complete understanding of the nature of the 5f electrons has been and continues to be a major scientific problem in condensed matter physics. Bulk and surface electronic structure studies of the actinides as also atomic and molecular adsorptions on the actinide surfaces provide a path towards this understanding. In this work, ab initio calculations within the framework of density functional theory have been used to study the adsorption of molecular CO2 and the corresponding partially dissociated (CO + O) and completely dissociated (C + O + O) products on the δ-Pu (111) surface. The completely dissociated C + O + O configurations exhibit the strongest binding with the surface (7.92 eV), followed by partially dissociated products CO + O (5.08 eV), with molecular CO2 adsorption having the lowest binding energies (2.35 eV). For all initial vertically upright orientations, the CO2 molecule physisorbs or do not bind to the surface and the geometry and orientation do not change. For all initial flat lying orientations chemisorption occurs, with the final state corresponding to a bent CO2 molecule with bond angles of 117°–130° and the elongation of the CO bond. For CO + O co-adsorption, the stable configurations corresponded to CO dipole moment orientations of 100°–172° with respect to the surface normal and the elongation of the CO bond. The most stable chemisorption cases correspond to anomalously large rumpling of the top Pu layer. The interactions of the CO2 and CO with the Pu surface have been analyzed using the energy density of states and difference charge density distributions. The nature and the behavior of the 5f electrons have also been discussed in detail in the context of this study.

IR-change and yellowing of polyurethane as a result of UV irradiation

In this investigation IR-change and yellowing of polyurethane as a result of UV radiation were studied. In the presence of UV radiation (200 h, λ > 300 nm), the synthesized aromatic polyurethane undergoes photodegradation with gradual change of its colour. The photochemical degradation of the polyurethane is associated with the scission of the urethane group and photooxidation of the central CH 2 group between the aromatic rings. These reactions are combined with the yellowing of the polyurethane surface. Analysis of the colour changes in PU surface during photodegradation was carried out by measuring CIEL ∗ a ∗ b ∗ colour components ( L ∗, a ∗, b ∗ and Δ E a , b ∗). FT-IR spectroscopy was used to study the chemical changes caused by UV irradiation. The colour difference of yellowing Δ a , b ∗ exhibits a systematic tendency to higher values with increasing irradiation time. Overall, Δ E a , b ∗ colour change correlates well with photodegradation of polyurethane by relative increase of the concentration of carbonyl group. Our results are in agreement with the quinone (yellow colour) formation as the chromophoric reaction product of polyurethane degradation.

Density functional study of CO2 adsorption on Pu(100) surface

The adsorption of CO2 on Pu（100） surface has been studied with periodic slab model by revised Perdew-Burke-Ernzerh approximation within the framework of density functional theory. The optimized results of adsorption energies and geometrical structures show that the H-C4O4-type adsorption is optimum adsorption mode with adsorption energy of 1.48 eV. The atomic population and density of states analysis indicate that the interaction between Pu atom and CO2 molecule results mainly from strong electron transfer and weak overlap-hybridization between molecular orbital 2πμ of CO2 molecule and Pu5f, Pu6d and Pu7s orbitals of surface Pu atom. The calculated activation barrier and adsorption energy CO2→CO+O dissociative reaction are 0.66 and 2.65 eV, respectively, which indicates the dissociative adsorption of CO2 on Pu（100） surface is favorable under the certain heat activation condition. The comparison of O2，H2，CO and CO2 adsorption on Pu（100） surface indicates the adsorption strength follows the ordering: O2，CO，CO2，H2 and O2，CO2，CO，H2 at lower and higher temperature, respectively.

Plasma Protein Adsorption and Platelet Adhesion on Heparin-Immobilized Polyurethane Films

Polyurethane surfaces were modified by covalent immobilization of different molecular weight heparins (fractionated Mw ~3000 Da, and unfractionated Mw ~17,000—19,000 Da) and examined by ESCA, AFM, and contact angle goniometer. The effect of these different surface-immobilized heparins on blood protein adsorption and on platelet adhesion, were examined after incubating the samples with platelet-poor and platelet-rich plasma. Protein adsorption kinetics was studied by electrophoresis and the platelets adhered on the surfaces were examined by SEM after incubation. The two heparin types clearly showed different behavior with respect to protein adsorption, especially in the early stages of blood plasma interaction. After a 5-min incubation in plasma, low molecular weight heparin-immobilized polyurethanes (PU-LMWH) showed three times less protein adsorption compared to unfractionated heparin-immobilized polyurethanes (PU-UFH). The total amount of adhered protein became more similar as the incubation time was extended. The morphology of adhered platelets on material surfaces demonstrated differences: PU-UFH had clusters with some pseudopodia extensions, while PU-LMWH surfaces had round-shaped platelets with little clustering. For contact times &gt;15 min, the amount of adsorbed proteins and adhered platelets on the heparinized PU surfaces decreased.

Surface characteristics of UV-irradiated polyurethane elastomers extended with α, ω-alkane diols

Polyurethane elastomers (PUEs) based on 4,4′-diphenylmethane diisocyanate (MDI), poly (ɛ-caprolactone) (PCL) and extended with series of chain extender (CE) were synthesized via two step polymerization technique. The synthesized samples were irradiated for 50, 100 and 200 h in an UV exposure unit as such the spectral distribution of the light is good match for terrestrial solar radiation. The modifications in the chemical structures of the PU before and after irradiation were characterized using Fourier transform infrared (FT-IR) technique. The effect of irradiation time and chain extenders length on surface properties were studied and investigated. Photo-oxidation of PU surface leads to fast increase in surface free energy and its polar component. Simultaneously, the work of water adhesion to polymer increases significantly during UV-irradiation. The higher changes in surface properties, observed by water absorption (%), equilibrium degree of swelling, as well as monitored by ATR-FT-IR and contact angle measurement, were found for the PU samples extended with higher number of methylene unit and irradiation time.

Hyper-branched poly(poly(ethylene glycol)methacrylate)-grafted surfaces by photo-polymerization with iniferter for bioactive interfaces

A new hyper-branched surface in which three species of architectures were constructed as stem chain, branched stem and twig chain-grafted branched chain of poly(poly(ethylene glycol)methacrylate) (poly(PEGMA)) by photo-polymerization using dithiocarbamyl group (DC) as iniferter was prepared and characterized. For these surfaces, radical copolymerization of styrene and an iniferter-activated chain that was previously synthesized was performed for using as base materials for surface coating. On a DC-activated surface, hyper-branched poly(PEGMA) was introduced by photo-polymerization and dithiocarbamylation. All modified surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Our results demonstrated that a highly hyper-branched graft architecture of poly(PEGMA) can be constructed on PU surface by photo-polymerization using dithiocarbamyl group as iniferter, in which first, second and third generation gave stem chain, branched chain and twig chain of poly(PEGMA), respectively. Our hyper-branched surfaces could be regulated by photo-irradiation time and might be controlled by feed amounts or other reaction conditions. This highly dense architecture of PEG chain with hydrophilicity and chain mobility, grafted on surface, is expected to be effectively utilized in bio-implantable substrates or micro- or nano-patterned surfaces for immobilization of bioactive molecules in biomedical fields.

Atomic adsorption on the (020) surface ofα−Pu: A density functional study

Adsorption of atomic carbon, nitrogen, and oxygen on the (020) surface of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$ has been investigated using the full-potential linearized augmented-plane-wave plus local basis method. The Perdew-Burke-Ernzerhof exchange-correlation functional is used and the surface is modeled by a four-layer periodic slab consisting of a total of $32\phantom{\rule{0.3em}{0ex}}\mathrm{Pu}$ atoms. Adsorption energies have been optimized with respect to the distance of the adatom from the Pu surface for four adsorption sites, namely, the onefold top, onefold hollow, twofold short-bridge, and the twofold long-bridge sites. To investigate the effects of spin-orbit coupling on the adsorption process, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling (NSOC) and one at the fully relativistic level with spin-orbit coupling (SOC). The short-bridge site was the most stable adsorption site for C, with chemisorption energies of 5.880 and $6.038\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at the NSOC and SOC levels of theory, respectively. The long-bridge site was the most stable adsorption site for N and O, with chemisorption energies at the NSOC and SOC levels of theory, respectively, being 5.806 and $6.067\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for N and 7.155 and $7.362\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for O. The respective distances of the C, N, and O adatoms from the surface for the most stable adsorption sites were found to be 1.32, 1.26, and $1.35\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Our results show that SOC adsorption energies are more stable than NSOC adsorption energies in the $0.14--0.32\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range. The work function and net spin magnetic moments, respectively, increased and decreased in all cases upon chemisorption compared to the bare surface. The local density of states and difference charge densities have been used to analyze the interaction between the adatoms and the substrate.

Density functional study of CO adsorption on Pu (100) surface

The adsorption of CO on Pu (100) surface were studied by the density functional theory (DFT). The calculation results show that the O-down adsorption is less stable than the C-down adsorption which is found to be a strong chemisorption. The stability of adsorption configuration of CO is hollow tilted &gt; hollow vertical &gt; bridge &gt; on-top. The interaction between Pu atom and CO molecule results mainly from the contribution of hybridized molecular orbital of CO molecule and hybridized orbital of surface Pu atom. A small activation barrier of 0.280eV is found for the dissociation of CO molecule in hollow tilted configuration, which indicates the dissociative adsorption of CO on Pu (100) surface at the lower temperature with dissociated C and O atoms favoring the hollow site of lowest energy.

Influence of Sources on Plutonium Mobility and Oxidation State Transformations in Vadose Zone Sediments

Well-defined solid sources of Pu(III) (PuCl3), Pu(IV) (Pu (NO3)4 and Pu (C2O4)2), and Pu(VI) (Pu02(NO3)2) were placed in lysimeters containing vadose zone sediments and exposed to natural weather conditions for 2 or 11 years. The objective of this study was to measure the release rate of Pu and the changes in the Pu oxidation states from these Pu sources with the intent to develop a reactive transport model source-term. Pu(III) and Pu(IV) sources had identical Pu concentration depth profiles and similar Pu release rates. Source release data indicate that PuIV(C2O4)2 was the least mobile, whereas Pu(VI)O2(NO3)2 was the most mobile. Synchrotron X-ray fluorescence (SXRF) revealed that Pu was very unevenly distributed on the sediment and Mn concentrations were too low (630 mg kg(-1)) and perhaps of the wrong mineralogy to influence Pu distribution. The high stability of sorbed Pu(IV) is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. Plutonium X-ray absorption near-edge spectroscopy (XANES) analysis conducted on sediment recovered at the end of the studyfrom the Pu(IV)(NO3)4- and Pu(III)(III)Cl3-amended lysimeters contained essentially identical Pu distributions: approximately 37% Pu(III), 67% Pu(IV), 0% Pu(V), and 0% Pu(VI). These results were similar to those using a wet chemistry Pu oxidation state assay, except the latter method did not detect any Pu(III) present on the sediment but instead indicated that 93-98% of the Pu existed as Pu(IV). This discrepancy was likely attributable to incomplete extraction of sediment Pu(III) by the wet chemistry method. Although Pu has been known to exist in the +3 oxidation state under microbially induced reducing conditions for decades, to our knowledge, this is the first observation of steady-state Pu(III) in association with natural sediments. On the basis of thermodynamic considerations, Pu(III) has a wide potential distribution, especially in acidic environments, and as such may warrant further investigation.

Ab initiofull-potential fully relativistic study of atomic carbon, nitrogen, and oxygen chemisorption on the (111) surface ofδ−Pu

First-principles total-energy calculations within the framework of generalized gradient approximation to density-functional theory have been performed for atomic carbon, nitrogen, and oxygen chemisorption on the (111) surface of $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$. The full-potential all-electron linearized augmented plane wave plus local orbitals method with the Perdew-Burke-Ernzerhof exchange-correlation functional has been employed. Chemisorption energies have been optimized with respect to the distance of the adatom from the Pu surface for four adsorption sites, namely, the top, bridge, hollow fcc, and hollow hcp sites, with the adlayer structure corresponding to a coverage of 0.50 of a monolayer in all cases. Computations were carried out at two theoretical levels, one without spin-orbit coupling (NSOC) and one with spin-orbit coupling (SOC). For NSOC calculations, the hollow fcc adsorption site was found to be the most stable site for C and N with chemisorption energies of 6.272 and $6.504\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, respectively, while the hollow hcp adsorption site was found to be the most stable site for O with chemisorption energy of $8.025\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. For SOC calculations, the hollow fcc adsorption site was found to be the most stable site in all cases with chemisorption energies for C, N, and O being 6.539, 6.714, and $8.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, respectively. The respective distances of the C, N, and O adatoms from the surface were found to be 1.16, 1.08, and $1.25\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Our calculations indicate that SOC has negligible effect on the chemisorption geometries, but energies with SOC are more stable than the cases with NSOC within a range of $0.05\char21{}0.27\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The work function and net magnetic moments, respectively, increased and decreased in all cases upon chemisorption compared with the bare $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$ (111) surface. The partial charges inside the muffin tins, difference charge-density distributions, and the local density of states have been used to analyze the Pu-adatom bond interactions.

Surface modification of polyurethane membranes using acrylic acid vapour plasma and its effects on the pervaporation processes

Acrylic acid (AA) vapour plasma treatment was used to modify the surface properties of polyurethane membranes (PU). The chemical changes produced after plasma treatment were measured mainly by X-ray photoelectron spectroscopy (XPS). AA plasma treatment increased in all the experimental conditions studied, the concentrations of carbonyl and ester groups at the PU surface compared with traditional oxygen plasma modification. The pervaporation (PV) results demonstrated that AA plasma treated PUs had much higher selectivity for the separation of methanol from methyl- t-butyl ether than untreated and O 2 treated PU membranes. This selectivity is maximum at 100 W and 1 min of AA plasma treatment time. HR-XPS spectra showed that a thin film with similar chemical properties to the poly(acrylic acid) was formed on top of the PU membrane after 5–10 W AA plasma treatments. AFM results of standard Si(1 0 0) substrates treated with AA revealed the formation of a ∼220 nm film at 5 W. However, Si substrates treated at 100 W, led to sputtering of the substrate. PU membranes treated with AA plasma at powers higher than 10 W showed a high C O content and a decrease in the COO contribution (C 1s envelope). This paper illustrates the importance of selecting the right plasma parameters to improve the efficiency of the PV process.

Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

An ab initio study of H 2 interaction with the Pu (1 0 0) surface

In our continuing efforts to understand adsorptions of environmental gases on actinide surfaces, we present here a comprehensive study of molecular hydrogen adsorption on plutonium (1 0 0) surface, using the generalized gradient approximation to density functional theory. Weak molecular adsorptions with a layer by layer alternate spin arrangement of the plutonium atoms have been observed and the vertical approaches at the center site are found to be the most favorable molecular adsorption sites for both non-spin-polarized and spin-polarized calculations, the adsorption energies for non-spin-polarized cases being slightly higher. A study of reaction barriers along with dissociative adsorptions of the hydrogen molecule has also been performed. The most favorable dissociation channel needs activation energies of 0.551 and 0.778 eV at the non-spin-polarized and spin-polarized levels, respectively, with considerably higher adsorption energies compared to molecular adsorptions. The 5f electrons are more localized in spin- polarized cases than their non-spin polarized counterparts. While charge transfer in the case of molecular adsorption is insignificant, the ionic part plays an important role in H–Pu bonding in dissociative adsorption, and the Pu 5f–H 1s hybridization is rather weak. Adsorption of hydrogen pushes the top of the 5f band away from the Fermi level. Except for interstitial sites, the work functions increase due to adsorptions of hydrogen.

A density functional study of molecular oxygen adsorption and reaction barrier on Pu (100) surface

Oxygen molecule adsorptions on a Pu (100) surface have been studied in detail, using the generalized gradient approximation to density functional theory. Dissociative adsorption with a layer by layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable compared to molecular adsorption. Hor2 approach on a bridge site without spin polarization was found to the highest chemisorbed site with energy of 8.787 eV among all the cases studied. The second highest chemisorption energy of 8.236 eV, is the spin-polarized Hor2 or Ver approach at center site. Inclusion of spin polarization affects the chemisorption processes significantly, non-spin-polarized chemisorption energies being typically higher than the spin-polarized energies. We also find that the 5f electrons to be more localized in spin-polarized cases compared to the non-spin-polarized counterparts. The ionic part of O-Pu bonding plays a significant role, while the Pu 5f-O 2p hybridization was found to be rather week. Also, adsorptions of oxygen push the top of 5f band deeper away from the Fermi level, indicating further bonding by the 5f orbitals might be less probable. Except for the interstitial sites, the work functions increase due to adsorptions of oxygen.