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This work addresses the ubiquitous presence of organic contaminants at inorganic solid surfaces and the improvement of XPS analysis selectivity to cope with it. Water contact angle measurements showed that the adsorption of organic contaminants occurs readily in ambient air, and faster and more extensively under high vacuum. It is stronger on stainless steel (SS) compared to silica and is significantly reduced when SS is sterilized by autoclaving. The reliability of XPS data was evaluated (selectivity, precision, accuracy) by correlations between spectral data incorporating a large amount of results obtained with different XPS spectrometers on SS and glass samples cleaned in different ways and conditioned with several biomacromolecules. The methodology used allows a discrimination to be made between contaminants and deliberately adsorbed biomacromolecules, and offers perspectives for tracking the source of contamination. Furthermore, a discrimination can be made between oxygen from the organic adlayer and oxygen from the substrate, and the O 1s component above 532.0 eV observed for SS is shown to be due to organic contaminants rather than adsorbed water. This approach offers new perspectives to examine the interactions (displacement or not) between contaminants and compounds of interest, e.g. proteins, at the stage of the adsorption process.

The spatial distribution of soil constituents at the micrometer scale is of great importance to understand processes controlling the formation of micro-aggregates and the stabilization of organic carbon. Here, the spatial distribution of organic and mineral constituents in Podzol horizons is studied by concerted measurements of (i) the content of various forms of Fe, Al, Si and C determined by selective extraction in the fine earth fraction of soil (f < 2 mm); (ii) the elemental composition of the clay fraction (f < 2 um) with lateral resolution using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and with surface selectivity using X-ray photoelectron spectroscopy (XPS); (iii) the specific surface area (SSA) of fine earth and clay fractions by krypton physisorption. The SSA of the fine earth in illuvial horizons is predominantly due to finely divided Fe oxides, including goethite, characterized by an equivalent particle size of about 10 mu m. Kaolinite platelets of about 2 gm size account for a large volume proportion in the clay fraction but have a minor contribution to SSA. Fe oxides and organic matter (OM) are intimately associated. Heterogeneity at the um scale is created by local variations in the relative amounts of kaolinite and Fe-OM associations. These two kinds of physical entities are in random mixture. Moreover, variation of C/Fe atomic ratios reveals sub-mu m scale heterogeneity. The latter is due to variation in the relative proportion of organic compounds and Fe oxides, indicating that aggregation of nanoparticles, and not only mere adsorption or pore filling, plays a role in these associations. In this regard, our results highlight that OM associated with Fe protects Fe oxides against physical displacement and that part of this associated OM is oxidizable by NaOCl treatment. These findings demonstrate that the concept of OM stabilization through association with Fe must be revisited when considering the sub-mu m scale level because fine Fe oxide particles can be easily dispersed during oxidation of associated carbon. Combination of physical fractionation and microanalysis (e.g. SEM-EDS, vibrational spectroscopy) offer promising perspectives to clarify the relationship between chemical composition and sub-inn scale architecture, and to better understand soil processes.

Glass and stainless steel (StSteel, AISI304-2R), previously cleaned with ethanol (-Eth) or with ethanol and UV–Ozone treatment (-UVO), were soiled with quartz suspensions in water and in a β-lactoglobulin (β-LGB) solution, and dried. The cleanability (ease of quartz particle detachment) in water was evaluated using a radial-flow cell. The soiling suspension containing β-LGB was used as such or after heating for 4 h at 75 °C, which provoked coagulation of about 75% of β-LGB. The substrate–solution interfaces were characterized by X-ray photoelectron spectroscopy (XPS) analysis of conditioned substrates and by contact angle measurements. The substrate surfaces are covered by a layer of organic contaminants which are not removed by pre-cleaning or are adsorbed from the surroundings. The presence of β-LGB in the soiling suspension leads to protein adsorption, but a significant amount of contaminants remains at the surface. For three of the substrates tested (Glass-Eth, Glass-UVO, StSteel-UVO) the increase of cleanability when the soiling suspension contained β-LGB may be explained by lower capillary forces acting upon drying. Capillary forces are proportional to the liquid surface tension and depend in a less important way on substrate contact angle. However the order of cleanability observed for the substrates soiled with a suspension of quartz particles in water (Glass-Eth≅Glass-UVO

Chitosan (Cs) and hydroxyapatite (Ha) were analysed by X-ray photoelectron spectroscopy (XPS). Phosphorylated Cs microparticles and hybrid Cs/Ha microparticles were prepared and analysed by XPS before and after immersion in a solution 1.5 times more concentrated than a simulated body fluid (SBF). The accuracy of spectrum recording, peak decomposition and peak component assignment was insured by a post-control of charge stabilization, and by the examination of correlations between spectral data guided by stoichiometry and charge balance. The concentration of organic oxygen was determined from the concentrations of the oxidized forms of carbon, allowing a sharper insight into speciation and O 1s peak shape. This indicated that the hydroxide ion of Ha, and hydrogenophosphate if present, give a contribution near 532.4 eV, which overlaps with organic oxygen. As a result of immersion in the 1.5*SBF solution, the formation of CaCO3 and of Ha material occurred. A quantification could be made for the constituents of biomaterial interest, contaminating salts and paraffin oil residues from the microparticle manufacturing process. The uncertainties regarding the nature of the model calcium phosphate used and the best marker for calcium carbonate were addressed by comparing the possible effect on the output, which was facilitated by using ternary composition diagrams. Whatever their formulation, the native microparticles were found to be coated by a thick layer of paraffin oil. The induction of calcium carbonate and phosphate precipitation or the retention of precipitates by the microparticles was favored by the presence of phosphate in the initial formulation either by phosphorylation or by incorporation of Ha.

The chemical compositions of the surface conditioning layers formed by different types of solutions (from isolated EPS to whole culture media), involving different bacterial strains relevant for biocorrosion were compared, as they may influence the initial step in biofilm formation. Different substrata (polystyrene, glass, steel) were conditioned and analyzed by X-ray photoelectron spectroscopy. Peak decomposition and assignment were validated by correlations between independent spectral data and the ubiquitous presence of organic contaminants on inorganic substrata was taken into account. Proteins or peptides were found to be a major constituent of all conditioning layers and polysaccharides were not present in appreciable concentrations; the proportion of nitrogen which may be due to DNA was lower than 15%. There was no significant difference between the compositions of the adlayers formed from different conditioning solutions, except for the adlayers produced with tightly bound EPS extracted from D. alaskensis.

A survey of the literature is made for the XPS analysis of food products (mainly spray-dried powders, which reveal a considerable surface enrichment in lipids) and of microorganisms and related systems (extracellular polymer substances and biofilms). This survey is used as a background for discussions and recommendations regarding methodology. Sample preparation methods reviewed are freeze drying, analysis of frozen hydrated specimens and adsorption of surface-active biocompounds on model substrates. Peak decomposition is a way to increase the wealth of information provided by the XPS spectra. It should be performed after a check that sample charge stabilization is satisfactory. Moreover, ensuring the precision needed to make comparisons within sets of samples may involve a trade-off between imposing constraints and generating information. The examination of correlations between spectral data in the light of chemical guidelines is useful to validate or improve peak decomposition and component assignment, and may also upgrade the chemical information regarding speciation. Further upgrading may be achieved by expressing marker XPS data in terms of concentrations of compounds of interest. Different methods of computation are discussed, providing a composition in terms of ingredients, classes of biochemical compounds, or various organic and inorganic compounds. As an alternative or complement to this deterministic approach, multivariate analysis of suitable spectral windows provides spectral components, which may be used for comparing samples, and which may have a direct chemical relevance or be used to identify features of interest.

The H bonding properties of silica gel surface hydroxyl have been studied by adsorbing series of organic compounds which are weak H bond acceptors and by observing the OH stretching band. While the data are consistent with the charge transfer model of H bond, a critical examination shows that their support to this theory, as well as the support of similar data reported for solutions, is not really significant. All the results, and particularly relationships found between absorption coefficients, show a complete similarity between the characteristics of H bonds formed on the solid surface and in solutions.

International audience; Among diatoms, Phaeodactylum tricornutum is a peculiar species that exists in three morphotypes with distinct cell wall structures and low silica context. X-ray photoelectron spectroscopy (XPS) analysis was performed on P. tricornutum and compared with diatom Thalassiosira pseudonana, the result provide new information on the chemical composition (elements, chemical functions, classes of biochemical compounds) of the cell surface. Two types of silicon were found condensed-silica (SiO2) and weakly polymerised silicate. Cells of T. pseudonana showed the highest concentration of silicon, with a majority in the form of condensed silica. For the fusiform and triradiate morpotypes of P. tricornutum, the majority of the small concentration of silican found was in the form of weakly polymerised silica. for all morphotypes of P. tricornutum, higher polysaccharide concentrations replaced silicas as a structural part of the cell wall. In both diatoms a high concentration of lipids was measured, in the form of carboxylic esters. Protonated nitrogen and phosphate were found in correlated amounts and attributed not only to phospholipids but also to phosphoproteins. Chloride ions characterised by a high electron density might be associated to the moieties. Sulfate groups were also detected, principally in P. tricornutum, and attributed to monoesters of polysaccharides.

Understanding the behavior of enzymes at solid surfaces requires coping with the complexity of the interfaces. Examples are given to illustrate key considerations: (i) influence of the adventitious contamination; the amount of glucose oxidase adsorbed on stainless steel in conditions producing an electrochemical effect is very low compared to the amount of organic contaminants; (ii) structure (multilayered, random) of an adsorbed phase containing an enzyme and other organic constituents (self-assembled monolayer, adventitious contaminants); (iii) competition between proteins for adsorption and influence of the adsorption procedure (simultaneous or sequential) and (iv) reality vs. expectation in enzyme (glucose oxidase) immobilization by tentative covalent grafting. The study of enzyme adsorption in several model systems (catalase on surface-modified carbon blacks, beta-glucosidase on clay at different pHs, beta-glucosidase on sand and surface-modified sand) showed that a strong adsorption, whether by electrostatic or hydrophobic interactions, provokes an extensive deactivation. After adsorption, which is a quick process, the enzyme activity may continue to decrease both in the adsorbed phase and in the solution owing to dynamic processes which involve the adsorbed enzyme and exchanges between the adsorbed phase and the liquid phase. (c) 2008 Elsevier Ltd. All rights reserved.

Grafting silicon wafers with CH(3)O(CH(2)CH(2)O)(n)C(3)H(6)-trimethoxysilane and -trichlorosilane (n=6 to 9) was performed in different conditions (solvent, reaction time, washing) in order to select procedures compatible with the design of nanostructured surfaces for biomaterial applications, using electron-beam lithography. After a first screening by principal component analysis (PCA), the X-ray photoelectron spectroscopy (XPS) data were analyzed by plotting the carbon to oxygen molar ratio vs the molar ratio of carbon singly bound to oxygen [CO] over carbon bound only to carbon and hydrogen [C(C,H)]. This was found to be a convenient method for discarding samples containing free polymerized silane. Such excess occurred as a result of insufficient washing or unsuitable solvent for the reaction (ether), as confirmed by AFM and thickness measured by X-ray reflectometry. Angle resolved XPS analysis indicated that the grafted silane layer had a 1-2 nm thickness and was covered by a thin layer of adventitious contaminant. As a result, the surface chemical composition obtained covered a broad range (O/C of 0.4 to 1.1; CO/C(C,H) of 2.5 to 6.5); variations could not be related to the nature of the silane reagent and no significant difference was found between hexane and toluene as solvent for the reaction. The grafted silane layer was not stable upon incubation during 24 h in phosphate buffered saline (PBS) at 37 degrees C, which mimics biological environments. As a consequence, the grafted wafers did not show protein repellent properties. This alteration was not observed at room temperature. XPS analysis demonstrated that silane layer detachment was due to a hydrolysis within the SiO(2) layer initially present at the wafer surface.

A series of homopolymer/random copolymer blends was used to produce heterogeneous surfaces by demixing in thin films. The chosen homopolymer is polystyrene (PS) and the random copolymer is poly(methyl methacrylate)-r-poly(methacrylic acid) (PMMA-r-PMAA), whose acidic functions could be used as reactive sites in view of further surface functionalization. The proportion of each polymer at the interface was deduced from X-ray photoelectron spectroscopy (XPS) data using, on the one hand, the O/C ratio, and on the other hand, decomposition of the carbon peak of the blends in two components corresponding to the carbon peaks of PS and PMMA-r-PMAA. Combining the information from XPS with atomic force microscopy (AFM) images, water contact angle measurements and PS selective dissolution, it appears that the surfaces obtained from blends with a high PS content (90/10 to 70/30) display pits with a bottom made of PMMA-r-PMAA, randomly distributed in a PS matrix. On the other hand, the surfaces obtained from blends with a low PS content (30/70 to 10/90) display randomly distributed PS islands surrounded by a PMMA-r-PMAA matrix. The characteristics of the heterogeneous films are thought to be governed by the higher affinity of PMMA-r-PMAA for the solvent (dioxane), which leads to the elevation of the PS phase compared to the PMMA-r-PMAA phase, and to surface enrichment in PMMA-r-PMAA.

protocol was set up to achieve good control and monitoring of the XPS analysis of hydrated specimens, which involves the ability to freeze the sample before its introduction into the spectrometer, to maintain ice under UHV and to control ice sublimation. The methodology was applied successfully to a model system consisting of a drop of water deposited on a film of triolein containing traces of a phospholipid (dipalmitoyl phosphatidylcholine). Phosphorus and nitrogen, characteristic of the phospholipid, were demonstrated to be accumulated at the spot of the initial oil-water interface. The redistribution of the phospholipid after oil melting could be monitored in real time. The method is promising not only to study surface rearrangements on hydrated systems after water removal but also to get analytical information on gas-water interfaces and on interfaces between two liquids differing according to volatility. Copyright (c) 2008 John Wiley & Sons, Ltd.

This contribution extends to typical food products the approach followed before to analyze microbial surfaces by XPS. Wheat-flour-based cakes with different formulations (absence of oil or egg products) and related nonbaked mixtures were analyzed by XPS. The C 1s, N 1s and 0 1s peaks can be decomposed into 4,2 and 3 components, respectively, with contributions that are due to well-identified chemical functions, typical of classes of biochemical compounds: proteins, carbohydrates, phospholipids (PL) and neutral lipids (NL). These attributions are supported by the analysis of ingredients, and by the 1 : 1 relationships between concentrations of elements and/or functional groups which demonstrate the consistency of the information regarding carbohydrates, proteins and PL: C 1s (286.2 eV) and O 1s (532.4 eV) contributions due to alcohol and ether; uncharged nitrogen (399.6 eV), and C 1s (287.6 eV) or O 1s (532 eV) contributions due to amide; phosphorous and positively charged nitrogen (402.3 eV) which are markers for PL. The concentrations of elements or functions ratioed to total carbon can be modeled on the basis of the known composition of model biochemical compounds, which leads to an evaluation of the surface composition expressed in wt% of these classes of compounds. Thereby, it was shown that surface accumulation, as compared to the bulk, increases in the order proteins < NL < PL. Moreover, the surface enrichment of PL compared to triglycerides was found to be increased after baking. Copyright (C) 2008 John Wiley & Sons, Ltd.

The cleanability of several model solid substrates (glass, stainless steel, polystyrene and polytetrafluoroethylene-PTFE) was studied with a radial-flow cell. Two soiling methods were used to mimic splashing with oil; a thin layer chromatography sprayer giving a narrower and more reproducible oil droplet size distribution was preferred. Glass was the most cleanable substrate, a result which may be consistent with the presence of a swelling gel-like layer at the surface. For the other substrates, the mechanical action exerted by the fluid played a major role in oil removal; however the detergent seemed to intervene after about 5-10 min, facilitating cleaning of PTFE. Oil droplet removal took place only at high wall shear stress, in zones where flow conditions where not well controlled making it impossible to evaluate the wall shear stresses needed for oil droplet removal. Evaluation of cleanability by using the radial-flow cell is restricted to variations of wall shear stresses in a range below 3 N m(-2). (C) 2007 Elsevier B.V. All rights reserved.

The surface chemical composition of nine strains of Bacillus subtilis was determined by X-ray photoelectron spectroscopy. Regressions between elemental concentrations and concentrations associated with different components of C1s, N1s, and O1s peaks provided a more precise validation of the procedure used for peak decomposition and allowed the assignment of the peak components to be completed or strengthened. The component of the O1s peak appearing around 531.2 eV was shown to contain a contribution of oxygen from phosphate groups (PO, PO-), the other contribution being due to oxygen involved in amide functions. The surface negative charge may be fully attributed to phosphate groups, despite the observation of two types of zeta potential vs pH curves. The strains exhibiting a sharp variation of the zeta potential (range of -35 to -55 mV) between pH 2 and 4.7 were characterized by a high phosphate surface concentration and by an excess (about 25%) of phosphate with respect to the sum of potassium, an exchangeable cation, and protonated nitrogen, attributed to protein or to alanine involved in teichoic acids.

The adsorption of collagen (type I from calf skin) was studied, comparing different collagen sources and using substrates which differ according to surface hydrophobicity (polystyrene, either native, with OH substitution of each repeat unit, with COOH substitution of a small fraction of repeat units, or surface modified by oxygen plasma discharge). The atomic force microscopy observation of the adsorbed layers showed that aggregation in the solution acts in competition with the formation of fibrils in the adsorbed phase; more aggregated solutions behave like less concentrated solutions regarding adsorption. The fibrils formed in the adsorbed phase are much smaller than the fibrils formed in the suspension, and, in contrast with the latter, do not show regular band pattern. It is confirmed that fibrils formation occurs more readily on more hydrophobic surfaces, which is tentatively attributed to a greater mobility of individual molecules adsorbed on more hydrophobic substrates. This interpretation is supported by previously published radiochemical measurements. However, the comparison of strongly different adsorption procedures (progressive on the one hand; quick and massive on the other hand) did not provide any additional clue.

Collagen (type I from calf skin) adsorption on polystyrene (PS) and plasma-oxidized polystyrene (PSox) was studied, using a quartz crystal microbalance with energy dissipation measurements (QCM-D) and atomic force microscopy (AFM) in tapping mode. Radio-labeled collagen was used to measure the adsorbed amount and the ability of adsorbed collagen to exchange with molecules in the solution. The results show that the collagen adlayer consists of two parts: a dense and thin sheet in which fibrils are formed (directly observed by AFM) and an overlying thick layer (up to 200 nm) containing protruding molecules or bundles which are in very low concentration but modify noticeably the local viscosity. The thickness and viscosity of the semi-liquid adlayer both increase with adsorption time and collagen concentration. Fibril formation near the surface also increases with time and collagen concentration and occurs more readily on PS compared to PSox. Radiochemical measurements show that this may be related to the larger mobility of molecules adsorbed on PS, presumably owing to a smaller number of binding points.

PAN-based carbon fibres obtained by carbonisation at relatively low temperature and submitted to high-temperature treatment and oxidation in wet conditions provided a range of materials differing according to surface composition and hydrophobicity. The adsorption of catalase by these fibres was studied by XPS and by activity measurements in the liquid and in the adsorbed state. Three typical situations are featured: limited adsorbed amount in the case of low hydrophobicity; significant adsorption and preservation of an appreciable enzyme activity for samples of moderate hydrophobicity; strong adsorption with deactivation of the enzyme in the case of high hydrophobicity.

X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic wetting measurements with the Wilhelmy plate method were used to characterize layers of three polystyrene-b-poly(acrylic acid) (PS-PAA) diblock copolymers (differing by their block lengths) created by dip coating or spin coating on glass and gold substrata. The copolymer layers were thick and continuous, whatever the substratum, with a preferred exposure of PS chains at the extreme surface for the copolymers with a small PS block. The surface roughness decreased as the PAA/PS block length ratio increased and was larger for dip-coated than for spin-coated layers. The dip-coated layers obtained with the copolymer with the large PAA block presented self-assembled nanostructures of worm-like type. Dynamic wetting measurements showed that the coated layers were able to reorganize, upon immersion-emersion in solution at different pH, due to the deprotonation and swelling of the PAA chains. This phenomenon was dependent on the block length and on the pH. A water contact angle typical of pure PS was obtained with the large PS block. A hydrophilic surface was obtained for the large PAA block after immersion at pH 11. In intermediate situations (large PAA block in water, large PS block at pH 11), the advancing contact angle was dependent on the time of contact with air subsequent to the preceding immersion. This demonstrates the possibility to modulate hydrophobicity-hydrophilicity switching and pH sensitivity of the coatings by the copolymer composition. (C) 2004 Elsevier B.V. All rights reserved.

The treatment of stainless steel surfaces with responsive polymers was investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. Poly (N-isopropylacrylamide) (PNIPAAM) is a temperature-sensitive polymer which is soluble in water below 32 degrees C (Lower Critical Solubility Temperature (LCST)) but collapses and aggregates above 32 degrees C. This polymer was adsorbed at 50 degrees C from solutions at different concentrations, followed by rinsing and different drying procedures. Thereby, a large variety of surface structures could be obtained, from smooth films to surfaces showing marked relief features due to residues of PNIPAAM aggregates. Two poly(styrene)b-poly(acrylic acid), PS-PAA, with different block lengths, were spin-coated on stainless steel and showed preferential exposure of PS blocks at the outermost surface. PNIPAAM-conditioning was shown to strongly reduce yeast cell adhesion and to facilitate the removal of oil soil due to its high water affinity and chain mobility below the LCST. PS-PAA coatings also reduced yeast cell adhesion; this may partly be due to a reorganization of the surface, leading to exposure of PAA chains in contact with water and thus to electrostatic repulsion of the yeast cells.

The supramolecular organization of collagen adsorbed from a 7 microg/ml solution on polystyrene was investigated as a function of the adsorption duration (from 1 min to 24 h) and of the drying conditions (fast drying under a nitrogen flow, slow drying in a water-saturated atmosphere). The morphology of the created surfaces was examined by atomic force microscopy (AFM), while complementary information regarding the adsorbed amount and the organization of the adsorbed layers was obtained using radioassays, X-ray photoelectron spectroscopy (XPS), and wetting measurements. The collagen adsorbed amount increased up to an adsorption duration of 5 h and then leveled off at a value of 0.9 microg/cm2. For samples obtained by fast drying, modeling of the N/C ratios obtained by XPS in terms of thickness and surface coverage, in combination with the adsorbed amount, water contact angle measurements and AFM images, indicated that the adsorbed layer formed a felt starting from 30 min of adsorption, the density and/or the thickness of which increased with the adsorption time. Upon slow drying, the collagen layers formed after adsorption times up to about 2 h underwent a strong reorganization. The obtained nanopatterns were attributed to dewetting, the liquid film being ruptured and adsorbed collagen being displaced by the water meniscus. At higher adsorption times, the organization of the collagen layer was similar to that obtained after fast drying, because the onset of dewetting and/or collagen displacement were prevented by the high density of the collagen felt.

Powder aerosols made of albumin, dipalmitoylphosphatidylcholine (DPPC) and a protein stabilizer (lactose, trehalose or mannitol) were prepared by spray-drying and analyzed for aerodynamic behavior, surface composition and physical state. The powders exited a Spinhaler inhaler as particle aggregates, the size of which depending on composition, spray-drying parameters and airflow rate. However, due to low bulk powder tap density (

The adsorption of collagen on polystyrene (PS) and polystyrene oxidized by oxygen plasma discharge (PSox) was studied as a function of time using radiolabeling, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Radiolabeling and XPS indicated that the initial step of adsorption was faster on PS than on PSox. AFM imaging under water revealed very different supramolecular organization of the adsorbed films depending on time and on the nature of the substrate: PS showed patterns of collagen aggregates at all adsorption times (from 1 min to 24 h); PSox was covered with a smooth layer except at long adsorption times (24 h), for which a mesh of collagen structures was observed. After fast drying, the collagen layer remained continuous and showed a morphology which recalled that observed under water. The mechanical stability of the adsorbed films was assessed under water by scraping with the AFM probe at different loading forces: no perturbations were created on PSox; in contrast, the layer adsorbed on PS was sensitive to scraping, the minimum force required to alter the collagen layer morphology increasing with time. These differences in the film properties were correlated with force measurements upon retraction: multiple adhesion forces were observed with collagen adsorbed on PS samples, whereas such an effect was never observed on PSox. The results show that the amount adsorbed and the organization of the adsorbed film respond differently to the adsorption time and that this is influenced by surface hydrophobicity. The quick initial adsorption on PS, compared to PSox, is thought to leave dangling collagen segments that are responsible for the observed morphology, for adhesion forces, and for lower mechanical resistance of the adsorbed layer.

Patterned surfaces were created using two polymers: polystyrene (PS) on the one hand, and either poly(methyl methacrylate) (PMMA) or poly(methyl methacrylate)-poly(methacrylic acid) (PMMA-PMAA) on the other hand. PMMA was dissolved in a solvent of PS; this solution was then spin-coated on a PS support that partially dissolved during the process. The materials were analyzed by water contact angle measurement, XPS, ToF-SIMS and AFM. The effect of the solvent on the final surface morphology was strongly marked. With chloroform, the acrylic polymer was the major surface constituent, possibly because of the high evaporation rate of this solvent. With toluene, which is a better solvent for PS compared to PMMA, the obtained surface was almost exclusively constituted of PS. The use of chlorobenzene provided inclusions of acrylic polymer in PS, both polymers being exposed at the outermost surface. The surface morphology presented rings, the interior of which consisted of the acrylic polymer, while the rest of the surface was made of PS. (C) 2004 Elsevier Ltd. All rights reserved.

Adsorption of collagen (300 nm length, 1.5 nm diameter) on poly(ethylene terephthalate) and the influence of Pluronic PE6800, a triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer, were investigated by the combination of three techniques. The adsorbed amounts of the two adsorbates were determined by radiolabeling. X-ray photoelectron spectroscopy was used to get quantitative information on the adsorbed layer. Selected samples were observed by atomic force microscopy (AFM) under water and in air; data on morphology, mechanical resistance, and molecular interactions were obtained. In the absence of Pluronic, two collagen layer morphologies were observed. Under water, at an adsorbed amount equal to half the maximum, collagen formed a dense granular layer; at the maximum adsorbed amount (equivalent to six layers of lying molecules), the adsorbed layer was soft, appeared as a pattern of elongated structures, and showed adhesion of the AFM probe with rupture lengths as long as several hundred nanometers. This was attributed to collagen molecules or bundles protruding into the solution. After fast drying, the collagen layer was smooth with a low surface fraction occupied by holes at the lower protein adsorbed amount, while it showed spindle-shape relief features at the maximum adsorbed amount. In the presence of Pluronic, the amount of adsorbed collagen was reduced considerably, due to rapid adsorption of the surfactant. In these conditions, the collagen layer obtained from high protein concentration solutions was also constituted by granules and was very sensitive to the alteration by the AFM probe.

PAN-based carbon fibres carbonised at relatively low temperature, i.e. type III carbon fibres, were submitted to heat treatment at 2300 °C (GR) or oxidation in nitric acid. The samples were characterised by XPS, FTIR, wetting measurements, gas adsorption, elemental analysis and acid/base titration. While oxidation only slightly affects the nitrogen concentration, it produces an appreciable change in the nature of the chemical functions, namely the conversion of pyridine-type nitrogen and quaternary nitrogen into aliphatic functions. Oxidation treatment modifies all the material constituting the fibre, the oxygen concentration being about 1.5 times higher at the fibre external surface compared with the whole material. Three components (531.2, 532.6 and 533.8 eV) are clearly identified in the oxygen XPS peak, allowing a comparison to be made between the whole material and the external surface regarding chemical species. The acidic groups are mainly carboxyl. Fibres submitted to extensive oxidation also show a high basicity, attributed mainly to calcium carboxylate. Although the acidic and basic groups present in the whole material can be titrated with aqueous solutions, the fibres develop only a very small surface area and no microporosity as determined by krypton adsorption. The material may be viewed as a sponge, collapsed when dry but able to swell in water and developing a high cation-exchange capacity.

Poly(ethylene terephtalate) (PET) crystallization was shown by atomic force microscopy (AFM) to occur at 85 degreesC in the first few nanometers near the polymer-air interface. The surface was fully transformed into spherulites after 30 min, while no signs of bulk crystallization were observed by FTIR. All the observed spherulites presented a nucleation centre, indicating that the crystallization process started at the surface of the film. Tapping mode AFM confirmed that the spherulites were not covered by an amorphous layer. The most probable explanation is a decrease of T-g near the surface. Due to the poor crystallization conditions, the constitutive units of the spherulites were;mail crystalline blocks. By changing the annealing time, it was possible to produce PET surfaces with different surface fractions consisting of semi-crystalline material (spherulites) and amorphous matrix. This provided a controlled surface heterogeneity on the submicrometer scale, with a contrast in terms of stiffness, roughness and swelling by organic solvents. (C) 2002 Elsevier Science Ltd. All rights reserved.

The surface of the bacterium Lactococcus lactis was investigated under water by contact mode atomic force microscopy (AFM) while varying the imaging parameters (imaging force, scanning velocity, scanning direction). Height images were three-dimensionally (3-D) reconstructed using GOCAD(C) software; this revealed grooves oriented along the scanning direction. Although the grooves were created by the scanning probe, they were not due to a single passage of the probe; the periodicity of the grooves was indeed always three to four times larger than the scanning line periodicity (ratio between the image size and the number of scanning lines). Upon repeated imaging at low force, the grooves were re-created each time with the same morphology; groove depth was increased at higher imaging force. The groove formation is tentatively explained by a deformation of the surface, due to compression or to adhesion, and its slow relaxation. While the grooves reveal a perturbation of the cell surface by the AFM probe, they provide pertinent information about the nanomechanical properties of the cell surface. (C) 2002 Elsevier Science B.V. All rights reserved.

To evaluate the influence of substratum surface characteristics on protein adsorption processes, we have investigated the adsorption (adsorbed amount, supramolecular organization) of collagen on model substrata exhibiting controlled topography and surface chemistry. Substrata were prepared in two steps: (i) gold deposition onto silicon wafers (smooth substrata) and onto a support with nanoscale protrusions created by colloidal lithography (rough substrata); (ii) functionalization with CH3 (hydrophobic) and OH (hydrophilic) groups, using alkanethiol self-assembly. Atomic force microscopy (AFM) images were recorded under water, prior to and after collagen adsorption, and the images were analyzed quantitatively using two independent approaches. On smooth substrata, collagen formed a similar to6 nm thick, homogeneous layer with low roughness on hydrophilic surfaces, and a similar to20 nm thick layer exhibiting elongated aggregated structures on hydrophobic surfaces. Film thickness measurements (AFM) together with X-ray photoelectron spectroscopy (XPS) revealed larger adsorbed amounts on hydrophobic surfaces compared to hydrophilic ones. On rough substrata, the adsorbed amounts were similar to those found on smooth substrata; however, the collagen molecules no longer formed aggregated structures on the hydrophobic surfaces. It is concluded that while the adsorbed amount is only affected by the surface chemistry, the supramolecular organization of the adsorbed layer is controlled both by surface chemistry and topography. The approach presented here will have great value in biophysics for investigating bioadsorption and bioadhesion processes on substrata of defined surface properties.

Cavity cuticles that surround the bacterial symbionts residing in the leaf cavities of the aquatic fern Azolla and Azolla leaf cuticle on the epidermis outside the cavity (outer cuticle) were submitted to XPS analysis. Differential charging enabled the signals of the microscopic sample and the support signals to be differentiated. The cavity cuticle has a composition similar to cutin. In comparison with the outer cuticle, it is characterized by a lower concentration of aliphatic chains and a higher concentration of oxygen-containing functions. This has implications in term of solute transport between the leaf and the bacteria. Copyright (C) 2002 John Wiley Sons, Ltd.

The influence of substrate hydrophobicity and biomacromolecules (dextran, bovine serum albumin – BSA) adsorption on the cleanability of surfaces soiled by spraying aqueous suspensions of quartz particles (10–30 lm size), then dried, was investigated using glass and polystyrene as substrates. The cleanability was evaluated using radial flow cell (RFC). The surface composition was determined by X-ray photoelectron spectroscopy (XPS). The interpretation of XPS data allowed the complexity due to the ubiquitous presence of organic contaminants to be coped with, and the surface composition to be expressed in terms of both the amount of adlayer and the mass concentration of adlayer constituents. When soiled with a suspension of particles in water, glass was much less cleanable than polystyrene,which was attributed to its much lower water contact angle, in agreement with previous observations on starch soil. Dextran was easily desorbed and did not affect the cleanability. The presence of BSA at the interface strongly improved the cleanability of glass while the contact angle did not change appreciably. In contrast, soiling polystyrene with quartz particles suspended in a BSA solution instead of water did not change markedly the cleanability, while the contact angle was much lower and the aggregates of soiling particles were more flat. These observations are explained by the major role of capillary forces developed upon drying, which influence the closeness of the contact between the soiling particles and the substrate and, thereby, the adherence of particles. The capillary forces are proportional to the liquid surface tension and depend in a more complex way on contact angles of the particles and of the substrate. The dependence of cleanability on capillary forces, and in particular on the liquid surface tension, is predominant as compared with its dependence on the size and shape of the soiling aggregates, which influence the efficiency of shear forces exerted by the flowing water upon cleaning.

The adhesion of Lactococcus lactis harvested in the exponential and stationary growth phases was examined on glass and on polystyrene with cells resuspended in water. A low adhesion density was observed with exponential cells whatever the substratum. Stationary cells adhered in large amount on polystyrene and not on glass. This adhesion behavior cannot be explained simply in terms of physicochemical properties of the surfaces. The attention is drawn on particular aspects which are not taken into consideration in classical approaches of cell adhesion. Atomic force microscopy showed that, after a forced contact, the bacterial surface sticks to the retracting AFM probe, indicating that the force applied when the cell comes in contact with the substratum may influence its adhesion. This may affect the relevance of adhesion tests in laminar conditions with respect to real situations. The X-ray photoelectron spectroscopy analysis of the substratum surface after detachment of adhering cells, on the one hand, and of evaporated cell supernatants, on the other hand, revealed that extracellular substances were released by L. lactis in the aqueous phase and at cell-substratum interface. They may have a critical effect on cell adhesion by increasing the ionic strength of the solution confined between the cells and the substrata and by bringing macromolecules at the interface. (C) 2001 Elsevier Science B.V. All rights reserved.

Adsorption of collagen on polystyrene (PS) and plasma-oxidized PS (PSox) was investigated using atomic force microscopy (AFM) as the main tool. The extent of alteration produced by the AFM tip upon scanning at controlled loading forces in water was used to obtain semiquantitative information on the properties of the interfacial phase. This information was completed by observing the extent of reorganization of the adsorbed collagen layer after drying. The PSox surface was altered by scanning at high loading force in water. This behavior, which was not observed on PS, was attributed to the presence of a solvated polyelectrolyte layer at the surface of PSox, as demonstrated by previous works. Collagen adsorbed on PS gathered together under the action of the AFM tip while no perturbation was observed for collagen adsorbed on PSox. After drying at low rate of a thin adsorbed collagen layer, a netlike structure was formed on PS, in contrast with PSox. These differences were attributed to the formation of a dense, mechanically strong mat of collagen molecules adsorbed on PSox and/or to anchoring of collagen molecular ends in the swollen surface layer of PSox, in contrast with PS.

The collagen layer formed by adsorption of collagen on native (PETn) and surface oxidized poly(ethylene terephtalate) (PETox) was studied by X-ray photoelectron spectroscopy and atomic force microscopy (AFM). On PETox, for adsorption times up to a few hours. the collagen molecules form a network, the nodes of which seem to be responsible for a dot-like morphology, On PETn, at very short adsorption times and consequently low surface coverages, the adsorbed molecules are displaced by the AFM tip. This effect reveals lower interactions between the collagen and the surface after drying compared to PETox. At higher coverages, the surface morphology is similar to that obtained for PETox. After an adsorption time of 24 h, an aggregation of collagen molecules is observed for both substrates. The results are discussed with regard to the interactions between collagen and the substrate in water, the events occurring during the drying process and the mobility of collagen molecules in the dry state, (C) 2001 Elsevier Science B.V. All rights reserved.

The molecular associations of N-( n-hexyl)hexanamide (PA-12MC) and N-( n-butyl)benzenesulfonamide (BBSA), taken as model compounds for polydodecamide (PA-12) and benzenesulfonamide plasticizers, respectively, were examined by Fourier transform infrared spectroscopy. In solution, the amide is distributed between a self-associated form, involving intermolecular hydrogen bonding, and isolated species. Dissociation is favored in an electron donor solvent due to hydrogen bonding between the amide and the solvent. Comparatively, BBSA has much less tendency to dissociate. Molecular modeling suggests that BBSA dimer associations exist in the condensed state thanks to intermolecular hydrogen bonds, while gas-phase infrared spectroscopy supports a stabilizing intramolecular interaction between the sulfonamide proton and the sulfonyl lone pairs for isolated molecules. Mixtures of the amide model compound with BBSA show the creation of a strong S-N-H … O=C hydrogen bond between the sulfonamide proton and the amide's carbonyl lone pairs. The amide N-H groups liberated from the former amide-amide interaction find themselves involved in a weaker C-N-H … O=S hydrogen bond (“free N-H”) with the plasticizer's sulfonyl lone pairs, the concentration of these bonds being maximum at mid-composition. For polyamide/BSAs mixtures, the accessibility of the amide and sulfonamide groups can restrict these associations. Mixtures of AAPA, an aliphatic amorphous polyamide, with a plasticizer bearing a branched alkyl chain, generate a low free N-H concentration and cause phase separation to occur, which confirms the steric sensibility of their interaction. A bifunctional benzenesulfonamide plasticizer appears to be less efficient than BBSA and leads to an increased dispersion in hydrogen bond distribution, both of which could be ascribed to the bulk of this molecule. Incorporation of BBSA in semicrystalline PA-12 leads to a behavior identical to that of AAPA/BBSA mixtures.

A strategy was developed to create a modulable polymer surface architecture (topography, chemical composition) at the nanometer scale. Therefore, collagen was first adsorbed on a poly(methyl methacrylate) (PMMA) substrate and dried at high or low rate to produce continuous or discontinuous layers, respectively. Solutions of PMMA in chlorobenzene were then spin-coated on top of these collagen layers. The obtained surfaces were investigated using atomic force microscopy and X-ray photoelectron spectroscopy. Spin-coating with pure chlorobenzene on the continuous collagen layer produced pits in the PMMA substrate through the collagen layer; spin-coating with PMMA solutions of increasing concentrations progressively led to the formation of a surface covered by particles made of PMMA and collagen, resulting from a combination of dissolution of PMMA from the substrate and deposition of PMMA from the solution. Spin-coating with pure chlorobenzene on the discontinuous collagen layer led to dissolution of PMMA and to its redeposition on the collagen pattern, which served as a template. This provided a surface entirely composed of PMMA, with cavities in the range of 0.1-1 mum diameter and 50-250 nm depth. In this case, the surface relief was independent of the PMMA concentration of the spin-coated solution, the substrate PMMA dissolution and redeposition being the dominant processes.

We report the first quantitative measurement of macromolecular stretching at the surface of living cells using combined atomic force microscopy imaging and force spectroscopy. The surface of dormant spores of Aspergillus oryzae was covered with a layer of crystalline-like nanostructures (rodlets) and showed no/weak adhesion forces. By contrast, the surface of germinating spores consisted of soft granular material, attributed to cell surface polysaccharides, and elongation forces reflecting macromolecular stretching were observed in the force-extension curves. These elongation forces were well described by an extended freely jointed chain model with a Kuhn length of 3.2 +/- 0.9 Angstrom and a segment elasticity of 3.9 +/- 1.8 N/m, which are consistent with values reported for the elastic deformation of single dextran and amylose polysaccharides. We therefore suggest that the elongation forces measured on germinating spores are due to the stretching of cell surface polysaccharides.

Chlorinated polypropylene (CPO) is commonly used as an adhesion promoter for paint on polypropylene/ ethylene - propylene copolymer blends (PP/EP). An adhesion mechanism frequently proposed in the literature is the CPO diffusion into the substrate, leading to molecular entanglement. It is shown here that CPO and PP/EP are immiscible. On the other hand, the use of radiolabelled CPO allowed quantification of CPO diffusion into PP/EP substrates as a function of several parameters and under conditions which simulate industrial practice. Diffusion requires substrate swelling by the solvent. This explains that it increases with the EP content of the material, with the solvent ability to swell the substrate, and with the thickness of the paint. For baked samples, diffusion passes through a maximum when the delay between CPO application and baking is varied. This is due to a balance between two processes working in opposite directions, i.e. substrate swelling and solvent evaporation.

The surface of oxygen-plasma-treated polystyrene (PSox) was investigated using X-ray photoelectron spectroscopy (XPS), streaming potential measurements and a dynamic study of the wetting properties at different pH (Wilhelmy plate method). The PSox surface is functionalized with various oxygen-containing groups, including carboxyl functions, and must be viewed as covered by a poly-electrolyte which swells depending on pH. The wetting hysteresis, its evolution upon repeated cycles and the influence of pH are controlled by the dissolution of functionalized fragments and the retention of water upon emersion; the retained water may evaporate progressively and allow macromolecule compaction and/or reorientation. Modification of the PSox surface upon aging in dry atmosphere, humid atmosphere, and water was studied using XPS and dynamic wetting measurements. Aging in water provoked the dissolution of PSox macromolecular chains, as indicated by adsorption of released fragments on a check PS sample placed nearby. However, the concentration of functionalized molecules at the surface of water-aged PSox was still sufficient to allow swelling at pH 5.6 and 11.0. Hydrophobicity recovery was faster in humid air (R. H. 95%) compared to dry air (R. H. 5%), due to the plasticizing effect of water. Hydrophobicity recovery upon aging in air was reversed quickly by immersion at pH 5.6 or 11.0, due to deprotonation and swelling.

Atomic force microscopy (AFM) was used to characterize, under water, the surface morphology and molecular interactions of two types of microbial cells: fungal spores (Phanerochaete chrysosporium) and bacteria (Lactococcus lactis), High-resolution deflection images showed that the spore surface was uniformly covered with patterns of rodlets that were several hundred nanometres in length and had a periodicity of similar to 10 nm, Such surface organization was not detected on the bacterial surface, which showed a sponge-like structure. Force-distance curves revealed very different molecular interactions for the two microorganisms: upon approach, no significant curvature was seen in the contact region for spores, contrary to bacteria, pointing to a difference in cell softness; and upon retraction, no adhesion forces were detected on spores but multiple unbinding events and elongation forces attributed to macromolecular bridging were observed on bacteria. These results show that AFM is a powerful tool for probing the surface properties of native microbial cells on the nanometre scale. Copyright (C) 2000 John Wiley & Sons, Ltd.

Polypropylene/ethylene - propylene copolymer blends (PP/EP) were characterized by time-of-flight (ToF), SIMS, by dynamic wetting and by atomic force microscopy and force modulation spectroscopy (AFM-FMM), In a first step, model systems of compression-moulded PP/EP physical blends were prepared. With these materials, ToF-SIMS provides linear relationships between the selected peak and the EP content in the material. This indicates that both phases are present at the surface in the same concentrations as in the bulk. However, the EP signal is weak. In dynamic wetting measurements with water, for each tested blend composition the advancing contact angle corresponds to that of PP and the receding contact angle corresponds to that of EP, This method is thus suitable for detecting the presence of the two phases at the surface even for low concentrations of one consituent, The force modulation image gives elastic contrasts between EP and PP and is thus able to reveal the surface morphology, In a second step, these methods were used to characterize injection-moulded PP/EP reactor blends. Both AFM-FMM and ToF-SIMS suggest that a PP skin covers EP nodules at the surface. This is confirmed by electron microscopy examinations of cross-sections. This surface phase segregation leads to the presence of PP in the first 100 mm of the surface and could be explained by preferential wetting of the mould by the phase with the lower viscosity, PP in this case. However, dynamic wetting reveals that the PP skin is not complete. Thus, a low EP concentration may be found at the surface, in the form either of EP nodules or of EP molecules having migrated through the PP skin, Copyright (C) 1999 John Wiley & Sons, Ltd.

A new method is proposed to correct for attenuation effects by adventitious organic contamination in quantitative XPS, The corrected intensity ratio I-X(o)/I-Y(o) involving two different substrate peaks is determined as the slope of the plot of I-X/I-C1s as a function of I-Y/I-C1s for samples covered with organic overlayers of varying thickness. The thickness of deposited organic overlayers does not need to be perfectly uniform provided that it does not vary by more than +/-40%. The sample surface can either be flat or present a random roughness (e.g. powders), Shadowing effects accompanying overlayer non-uniformity are taken into account by a simple model involving effective thickness and fractional coverage, which is shown to enhance greatly the accuracy of computed intensity ratios. Constraints of the method and possible implementations were examined with an NaCl powder covered with adventitious contamination, polystyrene (PS) and polydimethylsiloxane (PDMS). The most straightforward implementation of the method would be to record repeatedly the peaks of interest while decreasing the adventitious contamination overlayer thickness by thermal desorption, The error on I-Na2s(o)/I-Na1s(o) is +10%, with the apparent overlayer thicknesses varying from 1.1 to 0.3 nm, The method is applied to check the reliability of the spectrometer transmission functions reported previously by Weng et al, Copyright (C) 1999 John Wiley & Sons, Ltd.

Collagen adsorbed on poly(methyl methacrylate) (PMMA) was investigated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement, after either fast drying or slow drying. Quantification by :XPS of the amount of adsorbed collagen is shown to be influenced by the drying procedure; This is explained by AFM images, which reveal the formation of a net-like structure at slow drying rates. Comparison between the surface organization, as observed by AFM, surface models provided by XPS and contact angle measurements, indicates that chemically heterogeneous surfaces are produced at slow drying rates, PMMA being exposed at the outermost surface in the holes left by the collagen net. (C) 1999 Society of Chemical Industry.

Atomic force microscopy (AFM) has been used to investigate the organization of the collagen layer present on polymer substrata after adsorption and drying, while the adsorbed amount was monitored using X-ray photoelectron spectroscopy (XPS) and radiochemical measurements. Differences in the organization of the adsorbed collagen layer (surface coverage, layer thickness) observed by AFM fitted well with those found by models obtained from XPS and radiolabeling data. (C) 1999 Elsevier Science B.V. All rights reserved.

Atomic force microscopy (AFM) imaging and force-distance curves have been used to investigate, in situ, the nanoscale organization of collagen adsorbed on polymer substrata covering a wide range of surface roughness and surface hydrophobicity: bisphenol A polycarbonate (PC), poly(ethylene terephthalate) (PET), and poly(vinylidene difluoride) (PVdF) used as such or treated by an oxygen plasma discharge (ox). After collagen adsorption, PC and PCox showed patterned structures under water, the size of which was influenced by substratum surface oxidation. These structures are attributed to aggregated ends of collagen molecules. Extended rupture lengths were observed in the force-distance curves, suggesting that bundles of collagen molecules adhere to the AFM probe and are progressively torn out upon probe retraction. In contrast, on PET, PETox, PVdF, and PVdFox, adsorbed collagen formed a smooth, homogeneous film devoid of any topographic feature, and no extended rupture lengths were observed. After drying, holes in the collagen film were observed on PET and PVdF and not on PETox and PVdFox. The influence of substratum roughness and physicochemical properties is discussed, considering the mobility of collagen molecules at the interface.

The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. Copyright 1998 Academic Press.

Although hydrophobic forces are of great relevance in biological systems, quantifying these forces on complex biosurfaces such as cell surfaces has been difficult owing to the lack of appropriate, ultrasensitive force probes. Here, chemical force microscopy (CFM) with hydrophobic tips was used to measure local hydrophobic forces on organic surfaces and on live bacteria. On organic surfaces, we found an excellent correlation between nanoscale CFM and macroscale wettability measurements, demonstrating the sensitivity of the method toward hydrophobicity and providing novel insight into the nature of hydrophobic forces. Then, we measured hydrophobic forces associated with mycolic acids on the surface of mycobacteria, supporting the notion that these hydrophobic compounds represent an important permeation barrier to drugs.

Electrical charging of insulating samples during XPS is of direct concern for referencing the binding energy scale. Results are presented on charging of composite insulating samples that consist of an organic overlayer of polystyrene (PS) or polydimethylsiloxane (PDMS) deposited on NaCl particles. The samples were analysed using small-spot monochromatized radiation, the surface charge being stabilized with an electron flood gun. The charging shift of the NaCl substrate is influenced by three different factors: the total photoelectron flux, the energy of the electrons produced by the flood gun and the flux of electrons originating from the overlayer. The overlayer is acting as an additional electron source, which makes the substrate more negative and reduces inhomogeneities of the local potential affecting the peak full width at half-maximum. Comparison of substrate peak intensities with computed values showed that PS overlayers were less uniform compared to PDMS overlayers. The overlayer thickness and uniformity affect both the total photoelectron flux and the flux of electrons from the overlayer to the substrate. Overlayer charging, like substrate charging, is probably determined by the balance of electron fluxes in the phase considered. The kinetic energy of the photoelectron is determined by the electrical potential in the phase where photoemission occurs and not with respect to the sample surface. This was demonstrated by differential charging between the NaCl substrate and PS overlayer. (C) 1998 John Wiley & Sons, Ltd.

The contact angle of water was measured with the Wilhelmy plate method on apolar polymers: soft ethylene-propylene copolymer (EP), rigid polypropylene (PP), and their blends PP/EP (80 wt % PP) and EP/PP (20 wt % PP). Upon liquid displacement, the contact angles of the soft materials, EP and EP/PP, depended on viscoelastic energy dissipation due to solid deformation. This was observed in different situations: wetting and dewetting, liquid displacement due to the relative motion of the plain liquid with respect to the solid, and meniscus relaxation when that motion was stopped. The wetting hysteresis of polymer blends may be understood by considering viscoelastic energy dissipation and the static contact angles. The former depends on the elastic modulus while the latter is determined by the more hydrophobic phase and the less hydrophobic phase, for advancing and receding contact angles, respectively.

The surface physico-chemical properties (hydrophobicity, electrophoretic mobility, chemical composition) of a large set of top- and bottom-fermenting brewing yeasts, harvested in the exponential and stationary growth phases, have been investigated. Bottom- and top-fermenting strains showed different surface properties. Top strains were generally more hydrophobic than bottom strains, due to higher surface protein concentrations. Bottom strains possessed higher surface phosphate concentrations. The different profiles of electrophoretic mobility versus pH for top and bottom strains could be explained by modelling the surface charge according to the surface chemical composition as given by X-ray photoelectron spectroscopy. For bottom strains, the electrical properties were mainly controlled by phosphate, resulting in a low isoelectric point (pH 2 or below) and an electrophoretic mobility that did not become much more negative above pH 4. For the top strains, they were mainly determined by the balance of protonated amino- and carboxylate groups in proteins, which gave a high isoelectric point (pH 4) and an electrophoretic mobility changing greatly with pH in the range of 2 to 7. No difference in surface properties was found between flocculating and non-flocculating strains, or between cells from the exponential and stationary growth phases, even for strains where flocculation occurred during the transition from one growth phase to the other.