Plasma-oxidized polystyrene: Wetting properties and surface reconstruction

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

Structure and Chemical Composition of Layers Adsorbed at Interfaces with Champagne

The structure and the chemical composition of the layer adsorbed at interfaces involving champagne have been investigated using native champagne, as well as ultrafiltrate (UFch) and ultraconcentrate (UCch) obtained by ultrafiltration with a 10(4) nominal molar mass cutoff. The layer adsorbed at the air/liquid interface was examined by surface tension and ellipsometry kinetic measurements. Brewster angle microscopy demonstrated that the layer formed on polystyrene by adsorption or drop evaporation was heterogeneous, with a domain structure presenting similarities with the layer adsorbed at the air/liquid interface. The surface chemical composition of polystyrene with the adlayer was determined by X-ray photoelectron spectroscopy (XPS). The contribution of champagne constituents varied according to the liquid (native, UFch, and UCch) and to the procedure of adlayer formation (evaporation, adsorption, and adsorption + rinsing). However, their chemical composition was not significantly influenced either by ultrafiltration or by the procedure of deposition on polystyrene. Modeling this composition in terms of classes of model compounds gave approximately 35% (w/w) of proteins and 65% (w/w) of polysaccharides. In the adlayer, the carboxyl groups or esters represent about 18% of carbon due to nonpolypeptidic compounds, indicating the presence of either uronic acids in the complex structure of pectic polysaccharides or of polyphenolic esters. This structural and chemical information and its relationship with the experimental procedures indicate that proteins alone cannot be used as a realistic model for the macromolecules forming the adsorption layer of champagne. Polysaccharides, the other major macromolecular components of champagne wine, are assembled with proteins at the interfaces, in agreement with the heterogeneous character of the adsorbed layer at interfaces

Physico-chemical mechanisms affecting the adherence of starch granules on materials with different hydrophobicities

The factors influencing the adherence of starch were examined to improve the understanding of the mechanisms affecting soiling and cleanability. Therefore an aqueous suspension of starch granules was sprayed on four model substrates (glass, stainless steel, polystyrene and PTFE) and dried, and the substrates were cleaned using a radial-flow cell. The morphology of the soiled surfaces and the substrate chemical composition were also characterized. By influencing droplet spreading and competition between granule-substrate and granule-granule interfaces regarding the action of capillary forces, substrate wettability affected the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. The rate of drying had an influence explained by the duration left to capillary forces for acting. X-ray photoelectron spectroscopy demonstrated the presence of macromolecules, mainly polysaccharides, which were adsorbed from the liquid phase, or carried by the retracting water film and deposited at the granule-substrate interface. These macromolecules acted as an adhesive joint, the properties of which seemed to be influenced by the detailed history of drying and subsequent exposure to humidity. In summary, the substrate surface energy affects the adherence of starch aggregates by different mechanisms which are all linked together: suspension droplet spreading, action of capillary forces, direct interaction with starch particles and interfacial macromolecules

XPS analysis of chemical functions at the surface of Bacillus subtilis

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 (P=O, P–O−), 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

Surface functionalization of PEEK films studied by time-of-flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy

Using the wet chemistry method, the surface of poly(aryl ether ether ketone) (PEEK) him aas selectively modified to produce PEEE-OH, PEEE-COOH, PEEK-glutamine, PEEK-NH2 and PEEK-SO3H samples displaying, respectively hydroxyl, carboxyl, amino acid, amine and sulphonyl functions. All the samples were analysed by XPS and time-of-flight (ToF) SIMS; the experimental data provided by both techniques were in good agreement, and allowed the chemical nature and the yield of the functional groups introduced by the different surface derivatizations to be determined. Copyright (C) 1999 John Wiley & Sons, Ltd

Surface amination of PEEK film by selective wet-chemistry

Using 4,4'-dimethoxybenzhydrol as soluble mimic of the reduced poly(aryl ether ether ketone) (PEEK) monomer unit, we established the best experimental conditions to replace the hydroxyl group with an amine function, on the one hand, and to fix an amino acid residue, on the other hand. The selected strategies were then adapted to the surface functionalization of the PEEK-OH film obtained by reduction of the PEEK precursor. Thus, reaction with phenylcarbamate followed by LiOH hydrolysis gave the PEEK-NH2 film characterized by theta(w), multiple internal reflection (MIR) and X-ray photoelectron specstroscopy, (XPS). The PEEK-NH2 was further derivatized with 1,3-propanesultone. Reaction of PEEK-OH with N'-(9-fluorenylmethoxvcarbonyl) (L) glutamine followed by piperidine deprotection gave the PEEK-glutamine sim characterized by theta(w), MIR and XPS. (C) 1998 Published by Elsevier Science Ltd. All rights reserved

Antigen binding forces of single antilysozyme Fv fragments explored by atomic force microscopy.

We used atomic force microscopy (AFM) to explore the antigen binding forces of individual Fv fragments of antilysozyme antibodies (Fv). To detect single molecular recognition events, genetically engineered histidine-tagged Fv fragments were coupled onto AFM tips modified with mixed self-assembled monolayers (SAMs) of nitrilotriacetic acid- and tri(ethylene glycol)-terminated alkanethiols while lysozyme (Lyso) was covalently immobilized onto mixed SAMs of carboxyl- and hydroxyl-terminated alkanethiols. The quality of the functionalization procedure was validated using X-ray photoelectron spectroscopy (surface chemical composition), AFM imaging (surface morphology in aqueous solution), and surface plasmon resonance (SPR, specific binding in aqueous solution). AFM force-distance curves recorded at a loading rate of 5000 pN/s between Fv- and Lyso-modified surfaces yielded a distribution of unbinding forces composed of integer multiples of an elementary force quantum of approximately 50 pN that we attribute to the rupture of a single antibody-antigen pair. Injection of a solution containing free Lyso caused a dramatic reduction of adhesion probability, indicating that the measured 50 pN unbinding forces are due to the specific antibody-antigen interaction. To investigate the dynamics of the interaction, force-distance curves were recorded at various loading rates. Plots of unbinding force vs log(loading rate) revealed two distinct linear regimes with ascending slopes, indicating multiple barriers were present in the energy landscape. The kinetic off-rate constant of dissociation (k(off) approximately = 1 x 10(-3) s(-1)) obtained by extrapolating the data of the low-strength regime to zero force was in the range of the k(off) estimated by SPR

Photocleavable stabilizer for the preparation of PHEMA nanogels by dispersion polymerization in supercritical carbon dioxide

A new photo-sensitive diblock copolymer composed of a hydrophilic sequence of poly(ethylene oxide) (PEO) linked to a CO2-philic sequence of poly(1H,1H,2H,2H-heptadecafluorodecyl acrylate) (PFDA) by a light sensitive o- nitrobenzyl group was successfully synthesized by RAFT polymerization and used as stabilizer for the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in dispersion in ?,?,?-trifluorotoluene and supercritical carbon dioxide (scCO2). Thanks to this fluorinated stabilizer, well-defined particles of PHEMA down to 350 nm of diameter were produced in scCO2. Advantageously, the photocleavable group at the block junction of the stabilizer could be cleaved by exposing the particles to UV light so that the fluorinated block could be extracted in TFT or scCO2. As supported by X-ray photoelectron spectroscopy (XPS) analysis, up to 80 % of the fluorinated block of the stabilizer can be removed, leading to efficient swelling and dispersion of the resulting PHEMA nanogels in water

Nanometer scale organization of mixed surfactin/phosphatidylcholine monolayers.

Mixed monolayers of the surface-active lipopeptide surfactin-C(15) and of dipalmitoyl phosphatidylcholine (DPPC) were deposited on mica and their nanometer scale organization was investigated using atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). AFM topographic images revealed phase separation for mixed monolayers prepared at 0.1, 0.25, and 0.5 surfactin molar ratios. This was in agreement with the monolayer properties at the air-water interface indicating a tendency of the two compounds to form bidimensional domains in the mixed systems. The step height measured between the surfactin and the DPPC domains was 1.2 +/- 0.1 nm, pointing to a difference in molecular orientation: while DPPC had a vertical orientation, the large peptide ring of surfactin was lying on the mica surface. The N/C atom concentration ratios obtained by XPS for pure monolayers were compatible with two distinct geometric models: a random layer for surfactin and for DPPC, a layer of vertically-oriented molecules in which the polar headgroups are in contact with mica. XPS data for mixed systems were accounted for by a combination of the two pure monolayers, considering respective surface coverages that were in excellent agreement with those measured by AFM. These results illustrate the complementarity of AFM and XPS to directly probe the molecular organization of multicomponent monolayers