Bulk and surface modification of elastomers by electron beam irradation: Structure-property relationship

Bulk and surface modification of ethylene propylene diene monomer (EPDM) and fluoroelastomer by electron beam irradiation was investigated. The structure of the modified elastomers was analysed with the help of Infrared (IR) spectroscopy, Electron Spectroscopy for Chemical Analysis (ESCA) and gel content. Mechanical and dynamic mechanical properties of bulk modified fluoroelastomers and surface energy and frictional coefficient of the surface modified EPDMs were measured. The properties were correlated with the structure developed.     

Atomic force microscopy imaging of hair: correlations between surface potential and wetting at the nanometer scale

We report investigations of hair surface potential under wetting at the nanometric scale by atomic force microscopy (AFM). Surface potential imaging was used to characterize the electrostatic properties of the hair samples. We found that the surface potential noticeably increases along the edges of the cuticles. These results are correlated with wetting behavior of different liquids performed using AFM in noncontact mode.     

Image reversal for direct electron beam patterning of protein coated surfaces

Electron beam lithography (EBL) is used to create surfaces with protein patterns, which are characterized by immunofluorescence and atomic force microscopies. Both negative and positive image processes are realized by electron beam irradiation of proteins absorbed on a silicon surface, where image reversal is achieved by selectively binding a second species of protein to the electron beam exposed areas on the first protein layer. Biofunctionality at the cellular level was established by culturing cortical cells on patterned lines of fibronectin adsorbed on a bovine serum albumin background for 7 days in culture.     

Decomposition and decoloration of a direct dye by electron beam radiation

The wastewaters released by textile industries to the environment contain hazardous compounds like toxic refractory dye stuff at high concentration. In this study, electron beam irradiation-induced decoloration and decomposition of C.I. Direct Black 22 aqueous solutions were investigated. The influences of absorbed doses and initial dye concentration on the percent of decoloration, COD and pH of the solutions are described. The results show that the direct dye solutions can be effectively degraded by electron beam irradiation.     

Mapping nanometer and micrometer-scale structures at graphite surface by photoelectron diffraction

A series of C 1s photoelectron intensity angular distribution (PIAD) patterns from a crystalline graphite surface were mapped in two dimensions at intervals of 20 μm. Two kinds of PIAD patterns rotated by 30° from each other, corresponding to the two domains from the twinned crystal, were found. The standard deviation of the diffraction contrast was evaluated for each PIAD pattern from its intensity histogram. Surprisingly, we found that odd-number- (most probably single-) atom-height steps on the flat terrace region and their local atomic arrangement can be identified by two-dimensionally mapping the standard deviation values. Furthermore, we analyzed the photoelectron diffraction patterns and noticed that the normal direction of the sample surface at each point was slightly inclined differently. By connecting all the inclination angle data, the micrometer-scale corrugation of the sample surface was successfully visualized. Scanning photoelectron diffraction microscopy has been shown to be useful for the nanometer- and micrometer-scale structural imaging.     

Surface tailoring for controlled protein adsorption: effect of topography at the nanometer scale and chemistry

Protein adsorption behavior is at the heart of many of today's research fields including biotechnology and materials science. With understanding of protein-surface interactions, control over the conformation and orientation of immobilized species may ultimately allow tailor-made surfaces to be generated. In this contribution protein-surface interactions have been examined with particular focus on surface curvature with and without surface chemistry effects. Silica spheres with diameters in the range 15-165 nm with both hydrophilic and hydrophobic surface chemistries have been used as model substrates. Two proteins differing in size and shape, bovine serum albumin (BSA) and bovine fibrinogen (Fg), have been used in model studies of protein binding with detailed secondary structure analysis being performed using infrared spectroscopy (IR) on surface-bound proteins. Although trends in binding affinity and saturation values were similar for both proteins, albumin is increasingly less ordered on larger substrates, while fibrinogen, in contrast, loses secondary structure to a greater extent when adsorbing onto particles with high surface curvature. These effects are compounded by surface chemistry, with both proteins becoming more denatured on hydrophobic surfaces. Both surface chemistry and topography play key roles in determining the structure of the bound proteins. A model of the binding characteristics of these two proteins onto surfaces having differing curvature and chemistry is presented. We propose that properties of an adsorbed protein layer may be guided through careful consideration of surface structure, allowing the fabrication of materials/surface coatings with tailored bioactivity.     

Synthesis and hydrogen storage behavior of Mg-Co-H system at nanometer scale

There are few reports on the hydrogen storage behavior study of Mg-Co-H system in the literature, although Mg₂CoH₅ has a much higher hydrogen capacity than Mg₂NiH₄. This is due to the great difficulty in the synthesis of Mg₂CoH₅ and Mg₂Co in convenient conditions. Here we successfully synthesized the nanostructured Mg₂CoH₅ and Mg₂Co from Mg and Co nanoparticles prepared by hydrogen plasma-metal reaction method. The reaction mechanism of the synthesis of the Mg-Co-H system was studied. The morphology of the Mg-Co-H system in nanometer scale was observed. The hydrogen absorption curves and the pressure-composition isotherm (P-C-T) properties of the Mg-Co-H system were studied. The van’t Hoff equations and the formation enthalpies and entropies of the produced Mg₂CoH₅ and Mg₃CoH₅ were obtained. The results were discussed by comparing with the corresponding ones of Mg-Co-H system by other groups and the ones of nanostructured Mg-H and Mg-Ni-H systems by our group.     

Structural and physico-chemical studies on modification of polypropylene and its polyphenolic antioxidant by electron beam irradiation

As polypropylene (PP) is widely used in medical and pharmaceutical fields, the effect of sterilization on both the polymer and its additives must be taken into account. In this study, PP and its antioxidants Irganox 1010 and 1076 were electron beam irradiated in order to evaluate by Fourier transform infrared spectroscopy, differential scanning calorimetry and size exclusion chromatography, their structural and physico-chemical modifications. A good correlation between those analytical techniques has indicated the formation of oxidation products, chain scissions as well as crosslinking. The effect of the absorbed dose is underlined.     

Nanostructuring at the surface of low‐energy lead‐implanted silicon by electron beam annealing

Low‐energy lead ion implantation and high‐temperature electron beam annealing were used to study the potential of producing Pb nanostructures on Si. Pb⁺ ions were implanted at high dose into p‐type (100) Si to the depth of 8.0 nm. The implanted samples were annealed under high vacuum conditions with an electron beam at 200–700 °C for 15 s. Rutherford Backscattering Spectrometry (RBS) shows rapid out‐diffusion of Pb atoms above 400 °C. However, some Pb atoms are still present in the near‐surface region after annealing the implanted samples at 700 °C. Lead nanostructures were found on samples annealed above 300 °C. Annealing the samples at 450 °C causes the formation of nanostructures as tall as 4.1 ± 0.1 nm. Many of these are arranged in ‘web‐like’ strings that extend over micrometer distances. Occasionally, much larger nano‐features (as wide as 500 nm in diameter, average height of 1.5 nm) appear in the centre of the strings. Annealing samples well above the melting point of lead results in randomly distributed small nanometer‐sized Si nano‐dots. Copyright © 2008 John Wiley & Sons, Ltd.     

PEW: Photopolymerization by evanescent waves. II. Revealing dramatic inhibiting effects of oxygen at submicrometer scale

A simplistic model of photopolymerization by evanescent waves (PEW) has been introduced in a previous paper. This model predicts a linear dependence of the polymerized thickness on the logarithm of exposure time. It provides the general trend of the experimental data. The present work shows that the properties of the material and the chemistry of the system also have to be taken into account to fit the experiments more precisely. Evidence was provided that dissolved oxygen has a marked effect on gel dose. In PEW the reaction is induced in very small solution volumes, so that marked competition seems to take place between reaction and diffusion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2075–2085, 1999     

Monte Carlo model of the temperature rise at a GaAs surface under an electron beam

Scanning electron microscopy (SEM) has frequently been used to study semiconductor materials. It offers the possibility of obtaining reliable qualitative and quantitative information on relevant local material parameters. The temperature rise due to electron‐beam bombardment can influence some semiconductor parameters, which then will influence the SEM information. In this work we propose a model calculation based on the Monte Carlo (MC) method to calculate the temperature rise due to electron‐beam heating. The results show that the temperature rise increases with increasing numbers of electrons (electron‐beam current), and the inverse behavior is observed with respect to the electron energy (electron‐beam voltage). The decrease in temperature rise with depth is also obtained. Copyright © 2006 John Wiley & Sons, Ltd.     

Probing molecules adsorbed at the surface of nanometer colloidal particles by optical second-harmonic generation

It is observed that optical second-harmonic generation from molecules adsorbed at the surface of nanometer size colloidal particles occurs at angles as large as 90 degrees away from the fundamental beam direction. This phenomenon can be rigorously described by the nonlinear Rayleigh-Gans-Debye theory and used for probing molecules adsorbed on nanometer size colloidal particles.     

The direct resist-free deposition of a lithographic mask from vapor initiated by an electron beam

A dry resist-free process of electron-beam vapor deposition of an undecane precursor (C₁₁H₂₄) mask on SiO₂-on-silicon and copper-on-silicon substrates was studied. The band section was trapezoidal, and the band width at the base was much larger than the diameter of the electron beam and depended on the substrate (it was three or four times larger on copper than on SiO₂). In mask deposition on copper, the mask thickening rate v was found to depend strongly on the scan time τ_sc when scanning was performed along the band. When τ_sc changed from 20 ms to 13 s, v decreased by a factor of 7.4 (beam current 1.0 nA). This was probably caused by significant diffusion delay of precursor transport to the reaction zone during pixel time when τ_sc was 13 s. The ion-beam etching of the substrates through the deposited masks was performed (the SiO₂ substrate was etched with SF₆ ions, and the copper substrate, with Ar ions).     

电子束辐照与电化学还原联用技术——一种用于煤炭直接液化的新方法

对电子束辐照与电化学联用技术提高煤炭液化率的新型方法进行了研究。利用高能电子束对煤炭样品进行辐照,并通过四氢呋喃萃取出辐照后的可能产物并计算其提取率。实验结果发现,提取产率随着辐照剂量的增加而增加,并得到在氧气气氛下25 kGy的最佳辐照条件。辐照的样品进一步在氢氧化钠电解液中电化学还原液化,并采用元素分析法、傅里叶红外光谱法、阴极极化曲线法、核磁共振法和计时电流法等来检测辐照对煤炭电化学还原的影响。     

Patterning of DNA nanostructures on silicon surface by electron beam lithography of self-assembled monolayer

Nanoscale patterns of modified oligonucleotides are produced on octadecyltrimethoxysilane self-assembled monolayers at a silicon surface by electron beam lithography. DNA structures with feature sizes of the order of 250 nm were detected by epi-fluorescence microscopy.     

The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy

A technique for measuring the photoionization spectrum and the photoelectron emission threshold of a microscopic structured material is presented. The theoretical underpinning of the experiment and the accuracy of the measurements are discussed. The technique is applied to titanium silicide nanostructures and melanosomes isolated from human hair, human and bovine retinal pigment epithelium cells, and the ink sac of Sepia officinalis. A common photothreshold of 4.5 +/- 0.2 eV is found for this set of melanosomes and is attributed to the photoionization of the eumelanin pigment. The relationship between the photoionization threshold and the electrochemical potential referenced to the normal hydrogen electrode is used to quantify the surface oxidation potential of the melanosome. The developed technique is used to examine the effect of iron chelation on the surface oxidation potential of Sepia melanosomes. The surface oxidation potential is insensitive to bound Fe(III) up to saturation, suggesting that the metal is bound to the interior of the granule. This result is discussed in relation to the age-dependent accumulation of iron in human melanosomes in both the eye and brain.     

Nanometer‐scale surface modification by polymerization of tetrafluoroethylene on polymer substrates in supercritical fluoroform

Surface penetrated polymerization of tetrafluoroethylene (TFE) was carried out on a polycarbonate (PC) plate in supercritical fluoroform (scCHF₃). Since the high diffusiveness is one of peculiar features of supercritical fluids, TFE monomers and initiators (perfluorinated benzoyl peroxide) could penetrate into the surface of polymer substrates and be photo‐polymerized. After washing physisorbed homopolymers on the surface, polytetrafluoroethylene (PTFE) was found to penetrate into 50–800 nm depth from the surface and covered the PC surface in the proportion of 85%. The surface coverage density and the penetration depth could be controlled by adjusting of the pressure of scCHF₃. The TFE‐penetrated polymerization could be applied for various polymer plates such as polyethylene, polystyrene, polypropylene, poly(ethylene terephthalate), and polyimide. In addition to polymer plates, this technique could be applied to a cellulose paper, a nylon textile, and a porous PC membrane. The PTFE‐penetrated nylon textile showed a high resistance for washing test with detergents, compared with the commercial fluoropolymer‐sprayed nylon textile. The PTFE‐penetrated porous PC membrane showed high oxygen permeability (P/P = 5.2), compared with that of the untreated PC membrane (P/P = 3.5) in gas permeation experiments of O₂ and N₂. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1577–1585, 2008     

Suppression of lithium deposition at sub-zero temperatures on graphite by surface modification

Lithium deposition on graphite anodes is considered as a main reason for failures and safety for lithium ion batteries (LIB). Different amounts of carbon coating on the surface of natural graphite are used in this work to suppress the amount of lithium deposited at − 10 °C. Pulse polarization experiments reveal relative polarization of graphite anodes at various temperatures and show that lithium deposition is accelerated at lowered temperatures. Electrochemical experiments, along with photographs, scanning electron microscopy (SEM) images and ex-situ X-ray diffraction (XRD) data suggest that carbon coating not only suppresses the lithium deposition but also enhances the formation of LiC₆ at − 10 °C. The homogeneous potential profile on the graphite surface attained by the carbon coating explains such an improved low temperature performance, as it allows efficient Solid Electrolyte Interface (SEI) film formation, which is a prerequisite for safety LIB.     

Comparison of rheological behavior of branched polypropylene prepared by chemical modification and electron beam irradiation under air and N2

Chemical and electron beam irradiation methods were used to introduce a branched structure into polypropylene and propylene–ethylene copolymer. The chemical method was carried out in an internal mixer using initiator and TMPTMA monomer. In irradiation method, the polymer was irradiated by electron beam under air and nitrogen atmosphere. The branched structure in the modified polymer was confirmed by rheological measurements. While degradation was significant in chemical method, branching occurred efficiently by irradiation under air. Small amount of ethylene in the propylene copolymer promoted branching over degradation.     

Rationalization of the behavior of solid-liquid surface free energy of water in Cassie and Wenzel wetting states on rugged solid surfaces at the nanometer scale

The present work aims to contribute to the understanding at a molecular level of the origin of the hydrophobic nature of surfaces exhibiting roughness at the nanometer scale. Graphite-based smooth and model surfaces whose roughness dimension stretches from a few angstroms to a few nanometers were used in order to generate Cassie and Wenzel wetting states of water. The corresponding solid-liquid surface free energies were computed by means of molecular dynamics simulations. The solid-liquid surface free energy of water-smooth graphite was found to be -12.7 ± 3.3 mJ/m(2), which is in reasonable agreement with a value estimated from experiments and fully consistent with the features of the employed model. All the rugged surfaces yielded higher surface free energy. In both Cassie and Wenzel states, the maximum variation of the surface free energy with respect to the smooth surface was observed to represent up to 50% of the water model surface tension. The solid-liquid surface free energy of Cassie states could be well predicted from the Cassie-Baxter equation where the surface free energies replace contact angles. The origin of the hydrophobic nature of surfaces yielding Cassie states was therefore found to be the reduction of the number of interactions between water and the solid surface where atomic defects were implemented. Wenzel's theory was found to fail to predict even qualitatively the variation of the solid-liquid surface free energy with respect to the roughness pattern. While graphite was found to be slightly hydrophilic, Wenzel states were found to be dominated by an unfavorable effect that overcame the favorable enthalpic effect induced by the implementation of roughness. From the quantitative point of view, the solid-liquid surface free energy of Wenzel states was found to vary linearly with the roughness contour length.