Angular-dependent X-ray Photoelectron Spectroscopy Research Articles

Poly[oligo(2-ethyl-2-oxazoline) methacrylate] as a surface modifier for bioinertness

Surface modification of versatile polymeric materials without changing their bulk properties is one of the essential techniques for regulating their physical and chemical characteristics, and this technique can improve the functions of materials. In this study, a bottlebrush-type poly[oligo(2-ethyl-2-oxazoline) methacrylate] (P[O(Ox)nMA]) (n = 7 and 19) was synthesized as a surface modifier. This compound was mixed into poly(methyl methacrylate) (PMMA) as a matrix (PMMA/P[O(Ox)nMA]) with a weight ratio of 15%, and the aggregation state in the surface region was examined under air and aqueous environments via atomic force microscopy, contact angle measurement, angular-dependent X-ray photoelectron spectroscopy, and neutron reflectivity. The surface of the PMMA/P[O(Ox)nMA] films was flat at the subnanometer level and covered with the PMMA-rich phase. However, once the films contacted water, the surface was reorganized due to the migration of P[O(Ox)nMA]. The extent of the surface segregation was more remarkable for P[O(Ox)7MA] than P[O(Ox)19MA] due to the entropic factor. Concurrently, NIH3T3 fibroblast adhesion and serum protein adsorption on the film were more strongly suppressed for P[O(Ox)7MA] than P[O(Ox)19MA] because it formed a thicker diffused interface in the film with water. As a surface modifier, poly[oligo(2-ethyl-2-oxazoline) methacrylate] (P[O(Ox)nMA]) with two different degrees of polymerization (n = 7 and 19) of the side chain were mixed into poly(methyl methacrylate) (PMMA). Once the PMMA/P[O(Ox)nMA] films contacted with water, the surface was reorganized due to the migration of P[O(Ox)nMA]. The extent of the surface segregation was more remarkable for P[O(Ox)7MA] than P[O(Ox)19MA] due to the entropic factor, resulting that the fibroblast adhesion on the film were much better suppressed for P[O(Ox)7MA] than P[O(Ox)19MA].

Design of a Bioinert Interface Using an Amphiphilic Block Copolymer Containing a Bottlebrush Unit of Oligo(oxazoline).

We designed an amphiphilic block copolymer, poly(methyl methacrylate)-block-poly[oligo(2-ethyl-2-oxazoline) methacrylate] (PMMA-b-P[O(Ox)MA]), suitable for bioinert coating. Angular-dependent X-ray photoelectron spectroscopy and neutron reflectivity measurements revealed that the outermost surface of a dried film of PMMA-b-P[O(Ox)MA] was covered with the PMMA block-rich layer. Once the film came into contact with water, the P[O(Ox)MA] bottlebrush block was segregated toward the water interface. This structural rearrangement in the outermost region of the film resulted in the formation of the swollen oligo(oxazoline) layer with excellent bioinertness in terms of the suppression of serum protein adsorption and NIH3T3 fibroblast adhesion.

Precise determination of surface band bending in Ga-polar n-GaN films by angular dependent X-Ray photoemission spectroscopy

We present a systematic study of surface band bending in Ga-polar n-GaN with different Si doping concentrations by angular dependent X-ray photoelectron spectroscopy (ADXPS). The binding energies of Ga 3d and N 1 s core levels in n-GaN films increase with increasing the emission angle, i. e., the probing depth, suggesting an upward surface band bending. By fitting the Ga 3d core level spectra at different emission angles and considering the integrated effect of electrostatic potential, the core level energy at the topmost surface layer is well corrected, therefore, the surface band bending is precisely evaluated. For moderately doped GaN, the electrostatic potential can be reflected by the simply linear potential approximation. However, for highly doped GaN samples, in which the photoelectron depth is comparable to the width of the space charge region, quadratic depletion approximation was used for the electrostatic potential to better understand the surface band bending effect. Our work improves the knowledge of surface band bending determination by ADXPS and also paves the way for studying the band bending effect in the interface of GaN based heterostructures.

Adsorption, Deprotonation, and Decarboxylation of Isophthalic Acid on Cu(111).

The surface-assisted reaction of rationally designed organic precursors is an emerging approach toward fabricating atomically precise nanostructures. Recently, on-surface decarboxylation has attracted attention due to its volatile by-products, which tend to leave the surface during the reaction means only the desired products are retained on the surface. However, in addition to acting as the reactive site, the carboxylic acid groups play a vital role in the adsorption configuration of small-molecule molecular precursors and therefore in the reaction pathways. Here, scanning tunnelling microscopy (STM), synchrotron radiation photoelectron spectroscopy (SRPES), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been employed to characterize the monodeprotonated, fully deprotonated, and decarboxylated productsof isophthalic acid (IPA) on Cu(111). IPAis partially reacted (monodeprotonated) upon adsorption on Cu(111) at room temperature.Angular-dependent X-ray photoelectron spectroscopy reveals that IPA initially anchors to the surface via the carboxylate group. After annealing, the molecule fully deprotonates and reorients so that it anchors to the surface via both carboxylate groups in a bipodal configuration. NEXAFS confirms that the molecule is tilted upon adsorption and after full deprotonation. Following decarboxylation, the flat-lying molecule forms into oligomeric motifs on the surface. This work demonstrates the importance of molecular adsorption geometry for on-surface reactions.

Cyclodextrin inhibits zinc corrosion by destabilizing point defect formation in the oxide layer.

Corrosion inhibitors are added in low concentrations to corrosive solutions for reducing the corrosion rate of a metallic material. Their mechanism of action is typically the blocking of free metal surface by adsorption, thus slowing down dissolution. This work uses electrochemical impedance spectroscopy to show the cyclic oligosaccharide β-cyclodextrin (β-CD) to inhibit corrosion of zinc in 0.1M chloride with an inhibition efficiency of up to 85%. Only a monomolecular adsorption layer of β-CD is present on the surface of the oxide covered metal, with Raman spectra of the interface proving the adsorption of the intact β-CD. Angular dependent X-ray photoelectron spectroscopy (ADXPS) and ultraviolet photoelectron spectroscopy (UPS) were used to extract a band-like diagram of the β-CD/ZnO interface, showing a large energy level shift at the interface, closely resembling the energy level alignment in an n–p junction. The energy level shift is too large to permit further electron transfer through the layer, inhibiting corrosion. Adsorption hence changes the defect density in the protecting ZnO layer. This mechanism of corrosion inhibition shows that affecting the defect chemistry of passivating films by molecular inhibitors maybe a viable strategy to control corrosion of metals.

Angular dependent XPS study of surface band bending on Ga-polar n-GaN

Surface band bending and composition of Ga-polar n-GaN with different surface treatments were characterized by using angular dependent X-ray photoelectron spectroscopy. Upward surface band bending of varying degree was observed distinctly upon to the treatment methods. Besides the nitrogen vacancies, we found that surface states of oxygen-containing absorbates (O-H component) also contribute to the surface band bending, which lead the Fermi level pined at a level further closer to the conduction band edge on n-GaN surface. The n-GaN surface with lower surface band bending exhibits better linear electrical properties for Ti/GaN Ohmic contacts. Moreover, the density of positively charged surface states could be derived from the values of surface band bending.

Cyclodextrins in Corrosion Protection of Zinc

In corrosion protection, coatings separate a metal from the environment. Once a coating is mechanically damaged and the metal is exposed to a corrosive environment, electrochemical dissolution of the metal occurs in the defect. Consequently, cathodic oxygen reduction takes place at the metal/polymer interface, resulting in the cathodic disbondment of the coating.1 This cathodic delamination can be slowed down by changing the chemistry of the metal coating interface.2–4However, for a complete suppression of the cathodic delamination, the healing of the defect is required. Healing can be realized by adding corrosion inhibitors into the coating. To passivate the metal, such inhibitors must be released from the coating and transported to the defect. Organic corrosion inhibitors are widely used for a variety of metals. Because many of these inhibitors are poorly soluble, a sufficient release from the coating is rather difficult. This work will show that β-cyclodextrin (CD) can be used to facilitate the release of organic corrosion inhibitors, e.g. 2-mercaptobenzothiazole (MBT). CDs are cyclic oligosaccharides which allow the encapsulation of hydrophobic organic compounds, while their hydrophilic shell ensures sufficient solubility in aqueous phases. CDs are used e.g. in the pharmaceutical industry for drug delivery, including the controlled release of pharmaceutics in the body. In this work, model coatings were filled with organic corrosion inhibitors in the presence and absence of CD. The released inhibitor concentration from the coating was examined with UV-Vis spectroscopy as function of pH. An up to 5-fold increase of the released inhibitor concentration was observed in the presence of CD. The highest increase was observed at alkaline pH. In the presence of CD, electrochemical impedance spectroscopy (EIS) showed improved barrier properties of the coatings. By Scanning Kelvin Probe (SKP) experiments, the delamination velocity in the presence of CD was found to show a significant decrease compared to the control experiment. The potential in the mechanical defect rose to the passive potential under certain experimental conditions. After exposure of the mechanical defect to 0.1M KOH electrolyte, the delamination slowed down with time and stopped after ~10 h, accompanied by a rise of the defect potential.5 SKP control experiments with pure CD without corrosion inhibitor suggested furthermore that CD itself acts as corrosion inhibitor. Therefore electrochemical experiments were conducted in a classical three electrode setup. An inhibition efficiency of 95% for zinc was found by EIS at low chloride concentrations. Inspection of the zinc surfaces after electrochemical testing with scanning electron microscopy showed differences in the morphologies of the corrosion products. The presence of CD on the zinc surface was detected by Raman spectroscopy. In situ ellipsometric experiments showed no formation of a thick adsorption layer of CD, and no increase in the thickness of corrosion products. For an in depth understanding of the interaction mechanism of CD with zinc surfaces, angular dependent x-ray photoelectron spectroscopy (ADXPS) in combination ultraviolet photoelectron spectroscopy (UPS) was performed ex situ. It was found that CD changes the electronic structure of the surface oxide on zinc. In the presence of CD, the oxide contained less defects, i.e. became closer to an intrinsic semiconductor. The formation of such a defect-poor oxide suppresses charge transfer processes in electrochemical reactions. Therefore, CD adsorption inhibits corrosion. Oligosaccharides such as CD are environmentally friendly agents. This work shows the potential for a wider use of these agents in corrosion protection.

Dynamic covalent polymer brushes: reversible surface modification of reactive polymer brushes with alkoxyamine-based dynamic covalent bonds

Reactive poly(methacrylate)-based polymer brushes with radically exchangeable alkoxyamine units in the side chains were prepared on flat silicon substrates and their reactivity and surface properties were investigated. The reactive polymer brushes were prepared by surface-initiated atom transfer radical polymerization (ATRP) and the graft density of the brushes was estimated to be approximately 0.36 chains per nm2. Radical crossover reactions among the alkoxyamine units in the side chains of the polymer brushes and at the ends of the fluorinated polymer chains were carried out to produce polymer brushes with low surface free energies. Angular-dependent X-ray photoelectron spectroscopy (XPS) measurement suggested that the fluorinated polymer chains were predominantly attached to the outermost surface because of the size exclusion from the high graft density. In addition, the de-grafting reaction of the fluorinated polymer chains was also performed to confirm the reversibility of the radical crossover reactions. The surface properties of the polymer brushes after the grafting and de-grafting processes were characterized by XPS and contact angle measurements. The composition calculated from the XPS indicated that the reversible grafting of the fluorinated polymer chains proceeded successfully. The surface wettability of the polymer brushes also changed after the grafting of the fluorinated polymers. Furthermore, after the de-grafting of the fluorinated polymer chains, the peaks attributed to fluorine atoms completely disappeared from the XPS spectrum and the wettability of the surface after the de-grafting returned to that obtained before grafting.

Self-Assembled Organic Monolayers Terminated in Perfluoroalkyl Pentafluoro-λ6-sulfanyl (-SF5) Chemistry on Gold

Recently synthesized (Winter, R.; Nixon, P. G.; Gard, G. L.; Radford, D. H.; Holcomb, N. R.; Grainger, D. W. J. Fluorine Chem. 2001, 107, 23-30) SF5-terminated perfluoroalkyl thiols (SF5(CF2)nCH2CH2SH, where n = 2, 4, and 6) and a symmetric SF5-terminated dialkyl disulfide ([SF5-CH=CH-(CH2)8-S-]2) were assembled as thin films chemisorbed onto gold surfaces. The adsorbed monolayer films of these SF5-containing molecules on polycrystalline gold were compared using ellipsometry, contact angle, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and infrared spectroscopy (FTIR) surface analytical methods. The resulting SF5-dialkyl disulfide monolayer film shows moderate angle dependence in depth-dependent XPS analysis, suggesting a preferentially oriented film. The SF5-terminated perfluoroalkyl thiols exhibit angular-dependent XPS compositional variance depending on perfluoroalkyl chain length, consistent with improved film assembly (increasingly hydrophobic, fewer defects, and more vertical chain orientation increasing film thickness) with increasing chain length. Tof-SIMS measurements indicate that both full parent ions for these film-forming molecules and the unique SF5 terminal group are readily detectable from the thin films without substantial contamination from other adsorbates.

Surface segregation of chain ends in α,ω-fluoroalkyl-terminated polystyrenes films

α,ω-Fluoroalkyl-terminated polystyrenes (α,ω-PS(R f) 2) with various molecular weights were synthesized by an anionic polymerization. Then, chain end distribution in the surface region of the α,ω-PS(R f) 2 films was studied by angular-dependent X-ray photoelectron spectroscopy in conjunction with neutron reflectivity. The α,ω-PS(R f) 2 films annealed under vacuum exhibited surface localization of chain ends. Since the fluoroalkyl chain ends possess a lower surface free energy compared with the main chain part, they energetically prefer to partition to the surface. The extent to which the chain ends were segregated at the surface was examined as a function of molecular weight. Also, it was presented how surface orientation of the fluoroalkyl end groups was dependent on molecular weight. On the other hand, no segregation of the chain ends was observed at the surface of the α,ω-PS(R f) 2 film annealed in boiled water. This is because the chain ends with a lower surface free energy tend to stay away from the higher energy medium of the boiled water. This result reveals that the surface concentration of chain ends can be regulated by selecting an appropriate annealing condition based on surface thermodynamics.

An angular dependent X-ray photoemission study of Indium-tin-oxide surfaces

ABSTRACTThe surface properties of indium-tin-oxide (ITO) thin films treated by UV ozone or plasma were analyzed by angular dependent X-ray photoelectron spectroscopy (ADXPS) and by ultraviolet photoemission (UPS). The chemical composition, chemical states and the work function of the ITO surfaces were deduced. Our analysis indicate that ITO surface is Sn-rich. Both UV ozone and O-plasma treatments are most effective in removing surface hydrocarbon. Among all treatments, O-plasma treated surface achieved the highest work function of 4.4eV, whereas argon ion sputtered surface had the lowest work function of 3.9eV. Both O-plasma and UV ozone treatments increase the surface oxygen concentration. It is proposed that O2-ions diffuse into ITO. The diffusion length is about 50Å as deduced from ADXPS. The stoichiometry of the surface is the major factor in controlling the surface work function of ITO. A surface band bending model is proposed to account for the change of work function due to “oxidized” ITO surface after UV-ozone or oxygen plasma treatments.

Synthesis and Surface Properties of Fluorocarbon End-Capped Biodegradable Polyesters

We report the synthesis and characterization of a new class of materials based on combining hydrolytically degradable polyesters and fluorocarbon surface chemistry. These materials have surface properties which overcome some of the limitations of polymeric materials in controlled cellular or tissue adhesion properties. Fluorocarbon chains of two lengths (CF3(CF2)m(CH2)n, where F7C1 and F10C2 represent m = 6 and n = 1 and m = 9 and n = 2, respectively) have been synthesized as the terminal end groups to l- and dl-polylactides (PLA) and poly(lactide-co-glycolide) copolymers. Using both ring-opening polymerization and the substitution of the fluorocarbon at terminal hydroxyl groups, polyesters with 1, 2, and 4 fluorocarbon end groups were obtained (F-polyesters). Angular dependent X-ray photoelectron spectroscopy (XPS or ESCA) revealed that end groups are segregated at the surface. Further, the results show their the surface coverage of fluorocarbon groups increases with increasing the concentration and the length of fluorocarbon end groups. The surface composition of F-polyesters can be controlled by blending these polymers with polyesters or by changing the architecture of fluorocarbon end groups. From ESCA data of F-polyesters after in-vitro hydrolysis at pH = 11.4, results from the F-polyester with a longer fluorocarbon end group (F10C2-) show that the surface erosion occurs at the topmost surface region during the initial hydrolysis period. The F-polyester having a short fluorocarbon group (F7C1-) shows a progressive decrease of surface fluorocarbon concentration as a function of hydrolysis time. This result is explained by a longer retardation time for water permeation into the sample bulk of F10C2-l-PLA due to greater segregation of fluorocarbon groups at the topmost surface.

Angular-dependent photoemission studies of indium tin oxide surfaces

Indium tin oxide (ITO) surfaces were treated by solvent cleaning, by plasma of oxygen, argon, nitrogen and by argon ion (Ar+) sputtering. Angular-dependent X-ray photoelectron spectroscopy (ADXPS) and ultraviolet photoelectron spectroscopy (UPS) were used to determine the chemical composition, the chemical states and the work function after each treatment. It was found that oxygen plasma and nitrogen plasma chemically reacted with the ITO surfaces. Yet little etching of the surface can be observed after plasma treatments. Among all treatments, oxygen-plasma-treated ITO achieved the highest work function of 4.40 eV, whereas Ar+-sputtered ITO surface had the lowest work function of 3.90 eV. The stoichiometry of the ITO surface is shown to be the major controlling factor of the ITO work function.

Overlayer thickness determination by angular dependent X-ray photoelectron spectroscopy (ADXPS) of rough surfaces with a spherical topography

The influence of surface topography on overlayer thickness determination by angular dependent X-ray photoelectron spectroscopy (ADXPS) was investigated by a geometrical model with a surface topography consisting of hexagonal close-pack hemispheres or spherical segments. Calculations consider all tilting and shadowing effects including shadowing by neighboring segments. The results are compared to ADXPS experiments of monolayers of n-octanethiol and PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) on gold. Rough surfaces were prepared by hexagonal close-pack polystyrene latex beads of 500 nm diameter covered with 50 nm gold on a silicon wafer. Flatter topographies consist of a 200 nm evaporated gold layer on Si(100) and of Au(111) surfaces. Experimental data and the theoretical results of the model agree for the different topographies. Small deviations in the order of ≤10% between experimental data and model calculations, based on the straight line approximation (SLA) of electron emission, can be explained by elastic electron scattering. The model for hemispherical surfaces can also be extended to rough surfaces with a similar, but less defined, corrugation. Thickness determination is greatly facilitated at an off-normal ‘magic angle’ of approximately 55°, where the ratio of the observed and true overlayer thickness ( d obs and d 0, respectively) is almost constant, i.e. d obs/ d 0=1.6 for a large range of topographies. This value for the ‘magic angle’ is higher than the angle reported in the literature, i.e. approximately 35° obtained from a simple two-dimensional model [W.S.M. Werner, Surf. Interf. Anal. 23 (1995) 696] and 40–45° from a three-dimensional model of a spherical topography without neighbor-shadowing effects [P.L.J. Gunter, O.L.J. Gijzeman, J.W. Niemantsverdriet, Appl. Surf. Sci. 115 (1997) 342].

Pentafluoro-λ6-sulfanyl-Terminated Chlorosilanes: New SF5-Containing Films and Polysiloxane Materials

Two new SF5-terminated perfluoroalkylsilanesSF5(CF2CF2)nCH2CH2SiCl3 (n = 1 and 2)were synthesized by addition of trichlorosilane to the corresponding synthetic SF5-terminated perfluoroalkenes by hydrosilylation. Thin films of these SF5-silanes on clean silicon oxide substrates were characterized by ellipsometry, aqueous contact angle, and X-ray photoelectron spectroscopy (XPS) methods. The shorter SF5-silane film shows a hydrophobic interface with minimal angle dependence in depth-dependent XPS analysis, suggesting a poorly organized film. The longer SF5-silane exhibits a high aqueous static contact angle (106°) and angular-dependent XPS compositional variance consistent with improved film assembly (fewer defects and more vertical chain orientation). Bulk SF5-bearing materials were fabricated by silane hydrolysis, producing SF5-polymers and cross-linked networks bearing the unique SF5 perfluoroalkyl chemistry.

Protein Interactions with Poly(ethylene glycol) Self-Assembled Monolayers on Glass Substrates: Diffusion and Adsorption

Hydrophilic polymer chains, poly(ethylene glycol) (PEG), are attached to glass surfaces by silylation of the silanol groups on glass surfaces with (ω-methoxy-terminated PEG)trimethoxysilanes. We consider these tethered polymer chains to resemble self-assembled monolayers (SAMs) of PEG since the grafting process is entirely spontaneous. They are shown to exhibit excellent biocompatibility and represent a model system for studying the interactions of proteins with polymer surfaces. The PEG SAMs are prepared with two different molecular weight polymers (MW = 750 and 5000) and characterized with the techniques of angular-dependent X-ray photoelectron spectroscopy and atomic force microscopy. For the low molecular weight sample, the polymer chains tend to extend, forming a brush-like monolayer, whereas for the large molecular weight sample, the longer polymer chains tend to interpenetrate each other, forming a mushroom-like PEG monolayer on the surface. Interactions between a plasma protein, bovine serum albumin, and the PEG SAMs are investigated in terms of protein adsorption and diffusion on the surfaces by the technique of fluorescence recovery after photobleaching. The diffusion and aggregation behaviors of the protein on the two monolayers are found to be quite different despite the similarities in adsorption and desorption behaviors. The results are analyzed with a hypothesis of the hydrated surface dynamics.

The intrinsic toughness and adhesion mechanisms of a glass/epoxy interface

Glass/epoxy interfaces of sandwich specimens were fractured under steady-state conditions over a wide range of in-plane mode-mix. The plastic dissipation was calculated via finite element analysis and subtracted from the steady-state fracture toughness to obtain the intrinsic toughness of the interface. Mechanisms which contribute to the intrinsic toughness were found to include the thermodynamic work of adhesion, local inelastic deformations and polymer chain pull-out, but their combined energy was only approximately 15% of the intrinsic toughness. Angular dependent x-ray photoelectron spectroscopy of the glass surfaces after fracture revealed epoxy adsorbed to a depth of approximately 3 nm. Cleavage of epoxy strands was found to be the most significant mechanism contributing approximately 40% to the intrinsic toughness of the interface.

Voltammetric and XPS investigations of nickel hydroxide electrochemically dispersed on gold surface electrodes

Abstract A chemically modified electrode composed of mixed hydroxide and oxyhydroxide nickel film (6–8 nmol cm −2 ) on the gold substrate (Au ∣ Ni) was characterized by cyclic voltammetry and XPS techniques. The gold substrate electrodes were firstly electrochemically conditioned in 0.2 M NaOH by cycling the potential between −0.25 and 0.6 V versus SCE, then modified by cathodic electrodeposition of nickel hydroxide films. These nickel films were obtained either by voltage cycling (50 mV s −1 ) between 0.0 and −0.5 V (SCE) or at constant potential of −0.3 or −0.5 V using non-deaerated 50 mM Ni(NO 3 ) 2 solutions. X-ray photoelectron spectroscopy (XPS) characterisation and voltammetric behaviour of Au ∣ Ni electrodes in alkaline solutions are described. Continuous electrochemical cycling of the Au ∣ Ni electrodes induces significant changes of the nickel films in terms of crystallographic structures and chemical composition. Combination of XPS and electrochemical methodologies have demonstrated the ability to follow the morphological and chemical changes in alkaline solutions upon cycling potentials. Angular-dependent XPS measurements have demonstrated that electrochemical treatment induces the formation of a uniform film layer with the following chemical distribution: Au ∣ Ni(OH) 2 ∣ NiOOH. The electrocatalytic activity of the Au ∣ Ni electrodes is investigated in alkaline medium using glucose as a model compound. The favourable combination of active species such as gold and nickel leads to a sensing electrode with strong catalytic activity over a wide range of applied potentials.

Protein−Silicone Interactions: How Compatible Are the Two Species?

Protein-on-silicone and silicone-on-protein films were made by the sequential coating of the human serum albumin (HSA) onto silicone films on glass or vice versa. The silicones used were either trimethylsilyl-terminated poly(dimethylsiloxane) (unfunctionalized PDMS) or (triethoxysilyl)propyl-terminated poly(dimethylsiloxane) (functionalized TES−PDMS). Angular-dependent X-ray photoelectron spectroscopy (AD-XPS) and contact angle measurements (CA) were used to characterize the modified surfaces. Irrespective of the order of building the films, protein-on-silicone or silicone-on-protein both showed essentially identical surface compositions, suggesting a significant degree of mixing between the protein and silicone. The TES−PDMS was found to have a greater affinity for HSA: thicker and more homogeneous silicone films were found with TES−PDMS/HSA than with PDMS/HSA films.

Effects of silane coupling agents on the interphase and performance of glass-fiber-reinforced polymer composites

The properties of the fiber/matrix interphase in glass-fiber-reinforced composites can play a dominant rôle in governing overall composite performance. Understanding the interactions occurring at the interphase and being able to tailor them to give a desired composite property are of great importance. In this paper, a singlefilament model of a commercial glass-fiber-reinforcement manufacturing process was used to apply methacryloxy and amino silanes with one, two, and three silanols (mono-ol, diol, and triol) to two different glass fibers in a molecular model. Surface analyses by angular-dependent X-ray photoelectron spectroscopy (ADXPS), electric-kinetic analysis (EKA), and contactangle measurements were used to characterize the surface coatings. The micro-indentation technique was used to evaluate fiber/matrix interfacial adhesion. Changes observed in surface chemistry, micromechanics, and composite properties as function of the silanol type are correlated.