Effect of film ageing on the surface properties of lactoglobulin and lactoglobulin+sucrose stearate monolayers

The change in β-lactoglobulin and β-lactoglobulin+sucrose stearate spread monolayers over time (ageing effect) at room temperature was studied. Measurements of the surface pressure π-mean area per molecule A isotherms of the monolayers were used to probe any time dependent changes. The increase of the protein film area with time was attributed to protein unfolding. At certain ratios of surfactant to protein, a higher film area increase was observed. This correlated well with the excess film areas of 45 h aged films. The excess film areas for newly spread films of the same composition seemed to follow the opposite trend indicating that the protein–surfactant interactions change as the conformational changes of the protein molecules progress.     

Effective insulating properties of autooxidized monolayers using organic ditellurides

Dialkyl ditellurides adsorb on Au(111) surfaces by wet deposition to form highly resistive autooxidized monolayers (AMs) due to the automatic formation of oxidized tellurium species after the adsorption of ditellurides on the surfaces under air in contrast to the case of the lighter dichalcogenides such as disulfides and diselenides. The ditelluride AMs could be applied to the selective fabrication of effective resistance, ferroelectric layers, piezoelectric parts, and/or new imaging systems using the feature of tellurium oxide in small device circuits.     

Assembly of organic monolayers on polydicyclopentadiene

The first well-defined organic monolayers assembled on polydicyclopentadiene is reported. Commercial grade dicyclopentadiene was polymerized with the Grubbs' second-generation catalyst in a fume hood under ambient conditions at very low monomer to catalyst loadings of 20 000 to 1. This simple method resulted in a polymer that was a hard solid and appeared slightly yellow. Brief exposures of a few seconds of this polymer to Br 2 lead to a surface with approximately half of the olefins brominated as shown by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-infrared (ATR-IR) spectroscopy. The ATR-IR spectroscopy was carried out with the polymer in contact with a Ge hemisphere housed in a GATR accessory from Harrick. This brominated polydicyclopentadiene was immersed in DMF with 4-(trifluoromethyl)benzylamine to assemble a monolayer. The amines displaced Br on the surface to form a monolayer that exposed a CF 3 group on the surface. The surface was extensively studied by XPS using the method described by Tougaard to find the distribution of F within the surface layer. The ratio for the peak area, Ap, to the background height, B, measured 30 eV below the peak maximum was 109.8 eV. This value clearly indicated that F was found only at the surface and was not found within the polymer. A surface coverage of 1.37 amines per nm (2) was estimated and indicated that the monolayer was 28% as dense as a similar monolayer assembled from thiols on gold. Finally, a simple method to pattern these monolayers using soft lithography is described. This work is critically important because it reports the first monolayers on a relatively new and emerging polymer that has many desirable physical characteristics such as high hardness, chemical stability, and ease of forming different shapes.     

萃取有机相的微结构和性质的研究

本文用FTIR, 荧光, ICP/AES等方法研究了含稀土的HDEHP[二(2-乙基己基)磷酸, HA]-正庚烷的萃取有机相的结构和聚集态。结果表明: (1)不同稀土离子与萃取剂的配位能力不一样, La相似文献   

Effect of bias and temperature on the bulk and surface properties of gold-containing plasma-polymerized fluorocarbons

Gold-containing plasma-polymerized fluorocarbon thin films have been deposited in an RF glow discharge fed with hexafluoroethane, while a gold target was simultaneously sputtered. Tile temperatureT _s and RF-induced biasU _s of a third electrode, used as a substrate holder, were separately varied. The influence ofT _s andU _s on the plasma and file lihn characteristics were individually studied using actinometric optical emission spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and measurements of optical transmission and surface contact angles. IncreasingU _s (up to –200 V) andT _s (up to 90°C) resulted in similar effects, namely a higher degree of cross-linking, higher gold concentration, better film stability with time, and increased wettability. A key role of the energy flux of particles impinging on the growing surface has been shown to account far the experimental results.On leave from the Faculty of Mathematics and Physics, Charles University, Praha, Czechoslovakia.     

Suppression of aqueous surface hydrolysis by monolayers of short chain organic amphiphiles

Aqueous aerosols and other water surfaces in the environment may be coated with organic films, which can give rise to significant effects on gas-solution transport and surface reactivity. We have used acridine as a molecular fluorescent pH probe to examine the hydration of nitric acid and ammonia at both the uncoated and the organic-coated air-water interface. For uncoated samples, a transient decrease in pH is observed at the interface upon introduction of nitric acid vapour, followed by a relaxation to a final pH which is lower than the initial value. This long-time final change in pH is also measured in bulk pH measurements. Solutions having monolayer and sub-monolayer films of 1-octanol do not display the transient, but do show the same long-time change in pH. The degree of suppression of the surface pH transient depends directly on the amount of octanol present at the surface. Hydrolysis of ammonia at the water surface is also indicated by a surface pH transient which is also suppressed when a monolayer of octanol is present at the surface. Monolayers of butanol and of uncompressed stearic acid at the surface show little difference from the clean interface. The results are related to the concentration of available water at the interface.     

Morphology of dry solid-supported protein monolayers dependent on the substrate and protein surface properties

The morphologies of dry MrgA protein monolayers on different solid substrates prepared by a three-step procedure (adsorption from an incubation solution, rinsing to remove excess salt and protein, and drying) were investigated using atomic force microscopy. MrgA is a dodecameric iron-storage protein which can form hexagonal, two-dimensional (2D) crystalline monolayers on hydrophilic surfaces at low supersaturation. The formation of such two-dimensional crystals is heavily dependent on the pH and the salinity of the incubation solution as well as on the surface properties. Correlation of surface coverage with substrate charge, ionic strength, and pH indicates the dominance of electrostatic effects in adsorption, with the balance shifting between intermolecular repulsion and protein-substrate attraction. Close to the isoelectric point (pI) of MrgA, adsorption to the surface and the formation of 2D crystals are favored. By preparation of self-assembled monolayers of thiols with different end groups on template-stripped gold, the surface properties can be varied easily from high to very low protein affinity. The resulting patterns of the crystalline protein structures are novel and could be a starting point for further scientific study, e.g., solid-supported cocrystallization with DNA, and indeed developments with technological applications, such as mesostructured deposition of MrgA-caged nanoparticles.     

Effect of temperature on the behavior of surface properties of alcohols in aqueous solution

The influence of temperature on the behavior of surface properties of aqueous solutions has often been used to obtain information about solute structural effects on water.In this work, we present experimental results for surface tension of aqueous solutions of n-pentanol, n-hexanol, n-heptanol, and n-octanol at T = (283.15, 288.15, 293.15, 298.15, 303.15, and 308.15) K at several concentrations. The results were used to evaluate the limiting experimental slopes of surface tension with respect to mole fraction and the hydrophobicity constant of the Connors model at each temperature. The thermodynamic behavior of aqueous alcohol solutions is discussed in terms of the effect of the hydrocarbon chain on water structure.The temperature dependence of the limiting slopes of surface tension with respect to mole fraction, as well as the hydrophobicity constant derived from surface measurements, is interpreted in terms of alcohol hydration.     

Effect of mycolic acid on surface activity of binary surfactant lipid monolayers

In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli <50 mN/m. AFM images showed that the smooth surface topography of surfactant lipid monolayers was altered with addition of MA. Aggregates with diverse heights of at least two layer thicknesses were found in the presence of mycolic acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC-POPC and DPPC-CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis.     

Rational construction of self-assembly azobenzene derivative monolayers with photoswitchable surface properties

hoto-responsive azobenzene (ABZ) derivatives with different end groups (R) were employed to construct selfassembled monolayers (SAMs) on silicon substrates. The SAMs based on hydrophilic (4-(4'-aminophenylazo) benzoic acid, ABZ-COOH) show excellent reversible photoswitching performance with a large contact angle change of 35° under optimized process.     

Self-assembled functional organic monolayers on oxide-free copper

The preparation and characterization of self-assembled monolayers on copper with n-alkyl and functional thiols was investigated. Well-ordered monolayers were obtained, while the copper remained oxide-free. Direct attachment of N-succinimidyl mercaptoundecanoate (NHS-MUA) onto the copper surface allowed for the successful attachment of biomolecules, such as β-d-glucosamine, the tripeptide glutathione, and biotin. Notably, the copper surfaces remained oxide-free even after two reaction steps. All monolayers were characterized by static water contact angle measurements, X-ray photoelectron spectroscopy, and infrared reflection absorption spectroscopy. In addition, the biotinylated copper surfaces were employed in the immobilization of biomolecules such as streptavidin.     

Plasma surface modification of organic materials: comparison between polyethylene films and octadecyltrichlorosilane self-assembled monolayers

Low-pressure low-frequency NH3 plasmas have been used for the surface modification of bulk polyethylene films and of octadecyltrichlorosilane (OTS) self-assembled monolayers deposited on oxidized silicon wafers. The incorporation of nitrogen-containing groups by the plasma treatment has been followed by contact angle measurements and by X-ray photoelectron spectroscopy. The surface degradation of the OTS monolayers due to plasma etching has been measured separately by optical ellipsometry with subnanometric accuracy. Our data show clear evidence for the existence of an optimum treatment time, yielding a high density of NH2 functional groups without significant variation of the structural features of the organic material. Self-assembled monolayers appear as excellent model systems to characterize the effects of plasma discharges on polyolefins. In particular, they allow testing the influence of molecular orientation, packing density, and crystallinity on the final results.     

Self-assembly of organic monolayers on aerosolized silicon nanoparticles

A new method is described for surface functionalization of silicon nanocrystals. Organic monolayers were self-assembled via gas-phase adsorption of amines, alkenes, alkynes, and aldehydes onto the surfaces of aerosolized crystalline silicon nanoparticles of 12.2 nm diameter in an atmospheric pressure tube reactor. Assembly took place within 4 s at temperatures between 200 and 500 degrees C. The extent of adsorption was measured by using tandem differential mobility analysis (T-DMA), an on-line diagnostic method for measuring changes in particle size. Functionalized particles were further characterized by high-resolution transmission electron microscopy and diffuse reflectance Fourier transform infrared spectroscopy. The apparatus described in this work can be used for continuous mass production of functionalized silicon nanoparticles. Moreover, the overall strategy of using T-DMA for monitoring monolayer uptake could be generally applied to study surface processing of other aerosolized nanoparticle systems.     

Effect of the phase states of self-assembled monolayers on pentacene growth and thin-film transistor characteristics

To investigate the effects of the phase state (ordered or disordered) of self-assembled monolayers (SAMs) on the growth mode of pentacene films and the performance of organic thin-film transistors (OTFTs), we deposited pentacene molecules on SAMs of octadecyltrichlorosilane (ODTS) with different alkyl-chain orientations at various substrate temperatures (30, 60, and 90 degrees C). We found that the SAM phase state played an important role in both cases. Pentacene films grown on relatively highly ordered SAMs were found to have a higher crystallinity and a better interconnectivity between the pentacene domains, which directly serves to enhance the field-effect mobility, than those grown on disordered SAMs. Furthermore, the differences in crystallinity and field-effect mobility between pentacene films grown on ordered and disordered substrates increased with increasing substrate temperature. These results can be possibly explained by (1) a quasi-epitaxy growth of the pentacene film on the ordered ODTS monolayer and (2) the temperature-dependent alkyl chain mobility of the ODTS monolayers.     

Effect of temperature on the acid-base properties of the alumina surface: microcalorimetry and acid-base titration experiments

Sorption reactions on natural or synthetic materials that can attenuate the migration of pollutants in the geosphere could be affected by temperature variations. Nevertheless, most of the theoretical models describing sorption reactions are at 25 degrees C. To check these models at different temperatures, experimental data such as the enthalpies of sorption are thus required. Highly sensitive microcalorimeters can now be used to determine the heat effects accompanying the sorption of radionuclides on oxide-water interfaces, but enthalpies of sorption cannot be extracted from microcalorimetric data without a clear knowledge of the thermodynamics of protonation and deprotonation of the oxide surface. However, the values reported in the literature show large discrepancies and one must conclude that, amazingly, this fundamental problem of proton binding is not yet resolved. We have thus undertaken to measure by titration microcalorimetry the heat effects accompanying proton exchange at the alumina-water interface at 25 degrees C. Based on (i) the surface sites speciation provided by a surface complexation model (built from acid-base titrations at 25 degrees C) and (ii) results of the microcalorimetric experiments, calculations have been made to extract the enthalpic variations associated respectively to first and second deprotonation of the alumina surface. Values obtained are deltaH1 = 80+/-10 kJ mol(-1) and deltaH2 = 5+/-3 kJ mol(-1). In a second step, these enthalpy values were used to calculate the alumina surface acidity constants at 50 degrees C via the van't Hoff equation. Then a theoretical titration curve at 50 degrees C was calculated and compared to the experimental alumina surface titration curve. Good agreement between the predicted acid-base titration curve and the experimental one was observed.     

Influence of temperature and alkyl chain length on phase behavior in Langmuir monolayers of some oxyethylenated nonionic surfactants

We study the surface phase behavior in Langmuir monolayers of a series of nonionic surfactants of the general formula CnE1 with n=14, 16, and 18 by film balance and Brewster angle microscopy (BAM) over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure-area (pi-A) isotherms indicates a first-order phase transition in the coexisting state between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air-water interface. The formation of bright two-dimensional (2D) LC domains in a dark background visualized by BAM further confirms this observation. In addition to the cusp point at the onset of the LE-LC coexistence state, another cusp point followed by a small plateau is observed for the C14E1 and C18E1 monolayers, indicating a second phase transition between two condensed phases of different compressibility and tilt orientation of the molecules. This unusual two-step phase transition is explained by the Ostwald step rule. The C16E1 and C18E1 monolayers show a kink in their respective isotherms, after which the surface pressure increases steeply with only a little decrease in the molecular area, suggesting that the molecules undergo a transition from a tilted to an almost vertical orientation with respect to the water surface. The thermodynamic parameters for the condensation of the molecules in the LE-LC coexistence state were calculated by employing the 2D Clapeyron equation. The temperature coefficient of the critical surface pressure dpi(c)/dT values shows a decreasing trend from C14E1 to C18E1, suggesting that the condensation process becomes less and less prone to thermal perturbation as the chain length increases. For all the amphiphiles, the DeltaH values are found to be negative, suggesting an exothermic nature of condensation. The negative DeltaS values obtained from the relation DeltaH/T probably come from the restriction on the rotational and translational motion of the molecules constrained in a confined area in the LE-LC transition region.     

Electrochemical properties of self-assembled monolayers of tripod-shaped molecules and their applications to organic light-emitting diodes

Self-assembled monolayers of a tripod-shaped conjugated-thiol grafted onot Au(111) substrates are found to show electrochemically reversible oxidation and reduction and to improve electroluminescence performances of organic light-emitting diodes.     

DC- and RF-GD-OES measurements of adsorbed organic monolayers on copper

Our direct current (DC)- and radiofrequency glow discharge optical emission spectroscopy (RF-GD-OES) measurements of adsorbed organic monolayers were inspired by the work of Shimizu et al., who presented the first example of depth profile analysis of an adsorbed monolayer by RF-GD-OES in 2004. The great potential of RF-GD-OES for analyses of layers with thicknesses in the subnanometer range was surprising. Shimizu et al. discussed not only the qualitative detection of atoms of the organic monolayer (C, H, N, S), but also the determination of the different orientation of the molecules relative to the surface due to a significant peak sequence. This latter assumption was questioned in the analytical community. We intend to demonstrate the potential of the GD-OES technique for surface analysis in terms of reliability and reproducibility by using an advanced vacuum instrumentation and presputtering with silicon. It will be shown that comparable measurements can be reproduced not only with RF-GD-OES but, above all, also with DC-GD-OES. The experimental steps to adsorb thiourea molecules on a copper substrate are described in detail. Further experiments with other organic molecules, e.g. benzotriazole (BTA) or benzothiazole (BTH), disprove the predicted correlation between the orientation of the molecules relative to the surface and the occurrence of peak separation. Ultimately, a quantification of compounds of the organic monolayer in the case of adsorbed thiourea is achieved.