Variations In Surface Chemistry Research Articles

The effect of copolymer composition on the surface properties of perfluoroalkylethyl acrylates

AbstractThe surface properties of two perfluoroalkylethyl acrylic copolymers—aqueous, Zonyl®329 and solvent‐based, Zonyl®225—were studied. Zonyl®329 is a water‐based dispersion and Zonyl®225 a solvent‐based copolymer solution; both polymers have the same perfluoroalkyethyl side chains [F(CF2)nCH2CH2] but have different comonomer compositions. Thin films, prepared by dip coating onto mica and quartz, with and without annealing, were characterized by contact angle and by X‐ray photoelectron spectroscopy (XPS). The contact angle measurements showed little variation with polymer and with substrate, consistent with the supposition that the perfluoroalkylethyl chains aggregate on the surface and thus dominate surface properties, irrespective of the composition of the rest of the polymer. XPS revealed only small variations in surface chemistry for studied films. Annealed films showed improved segregation for solvent‐based Zonyl®225, which has both hydrocarbon alkyl and perfluoroalkylethyl side chains; the presence of hydrocarbon alkyl chains enables the perfluoroalkylethyl chains to reorganize after annealing. Depending on the external conditions, this thermal treatment can enable more perfluoroalkylethyl chains to reach the film surface (solid/air interface), leading to a reduction in the dispersive‐dominant surface and enhancement in perfluoroalkylethyl segregation. This suggested that perfluoroalkylethyl side chains dominate the surface properties, which are thus not dependent on substrate, backbone composition, or formulation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Bubble formation in NiCr splat on aluminum substrate during plasma spray: Surface chemistry effect

NiCr single splats were plasma-sprayed on aluminum substrates which were modified by thermal treatments over a range of specific temperatures. It was observed that the splat morphologies changed from highly fingered splats to disk splats with increasing thermal treatment temperature. In addition, the density of the bubble pores which formed at the underside of NiCr splats significantly reduced with an increase of substrate temperature. X-ray photoelectron spectroscopy was used to examine the variation of surface chemistry with thermal treatment. The release of water from the dehydration of an oxyhydroxide layer, which was found to form on the substrate surface, was strongly correlated with the splat morphology and bubble formation at the splat underside. It is proposed that the water desorption from the substrate surface causes turbulence in the spreading process of the splat and the bubble formation at the splat underside, which leads to the splashing of the splat. Preheating or heating the substrate during spraying can partly remove the water prior to spraying, thereby greatly improving the contact between the splats and the substrate which enhanced the formation of a disk splat and significantly reduced the bubble formation at the splat underside.

Controlling Film Morphology in Conjugated Polymer:Fullerene Blends with Surface Patterning

We study the effects of patterned surface chemistry on the microscale and nanoscale morphology of solution-processed donor/acceptor polymer-blend films. Focusing on combinations of interest in polymer solar cells, we demonstrate that patterned surface chemistry can be used to tailor the film morphology of blends of semiconducting polymers such as poly-[2-(3,7-dimethyloctyloxy)-5-methoxy-p-phenylenevinylene] (MDMO-PPV), poly-3-hexylthiophene (P3HT), poly[(9,9-dioctylflorenyl-2,7-diyl)-co-benzothiadiazole)] (F8BT), and poly(9,9-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylendiamine) (PFB) with the fullerene derivative, [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). We present a method for generating patterned, fullerene-terminated monolayers on gold surfaces and use microcontact printing and Dip-Pen Nanolithography (DPN) to pattern alkanethiols with both micro- and nanoscale features. After patterning with fullerenes and other functional groups, we backfill the rest of the surface with a variety of thiols to prepare substrates with periodic variations in surface chemistry. Spin coating polymer:PCBM films onto these substrates, followed by thermal annealing under nitrogen, leads to the formation of structured polymer films. We characterize these films with Atomic Force Microscopy (AFM), Raman spectroscopy, and fluorescence microscopy. The surface patterns are effective in guiding phase separation in all of the polymer:PCBM systems investigated and lead to a rich variety of film morphologies that are inaccessible with unpatterned substrates. We demonstrate our ability to guide pattern formation in films thick enough to be of interest for actual device applications (up to 200 nm in thickness) using feature sizes as small as 100 nm. Finally, we show that the surface chemistry can lead to variations in film morphology on length scales significantly smaller than those used in generating the original surface patterns. The variety of behaviors observed and the wide range of control over polymer morphology achieved at a variety of different length scales have important implications for the development of bulk heterojunction solar cells.

ToF‐SIMS Imaging of DBD‐Plasma‐Printed Microspots on BOPP Substrates

AbstractImaging ToF‐SIMS has been applied to characterize the surface chemistry variations across small areas produced by a DBD‐type plasma printing technique on a BOPP substrate using pure nitrogen and a nitrogen‐hydrogen gas mixture. CH4N+ and CNO− secondary ions are detected with high yields remote from the discharge region. They are discussed to be due to surface modifications of the substrate by metastable gas‐phase species. On the other hand, surface species exist that are preferentially formed by reactions of the substrate with short‐lived species which are only present close to the plasma discharge region. A C3H8O+ secondary fragment ion is assumed to be a key fragment of such a surface species.magnified image

XPS study of the surface chemistry of Ag-covered L-CVD SnO 2 thin films

In this paper, we present the results of X-ray photoelectron spectroscopy characterization of SnO 2 thin films prepared by laser chemical vapour deposition (L-CVD) and subsequently covered by Ag atoms just after deposition and after long-term exposed to dry air, subsequent annealing in ultra high vacuum at 400 °C and dry air oxidation at 400 °C. Using the standard analytical procedure based on atomic sensitivity factors, the variation of surface chemistry defined in terms of the relative concentration of the main components of the films after the above-mentioned procedures has been determined. It was confirmed that after dry air exposure as well as dry air oxidation, the layers undergo an oxidation reaching almost SnO 2 stoichiometry. Besides, during ultra high vacuum annealing, the films undergo reduction to almost SnO stoichiometry. At the same time, Ag atoms deposited at the top of layers diffuse into the subsurface layers. This was confirmed by X-ray photoelectron spectroscopy depth profiling analysis.

Study of NO adsorption on activated carbons

Activated carbons (ACs) with varied porous textures and surface chemistry were studied for NO removal under different test conditions at temperatures below 100°C. When oxygen is absent, there is almost no NO removal. When oxygen is present ACs act both as a catalyst for NO oxidation and as an adsorbent for NO adsorption. NO conversion is correlated with the presence of narrow micropores and is independent of surface area. ACs with an average micropore size around 7Å exhibit the best NO removal capacity. NO rather than NO2 was observed to be the main adsorbed species during the initial period of adsorption. NO2 adsorption and NO2 gas release start only after the carbon surface was rapidly oxidized during the early stage of adsorption. The decomposition of NO2 formed through NO oxidation was believed to be responsible for the rapid carbon surface oxidation and NO chemisorption.

Manufacturing a nanometre scale surface topography with varying surface chemistry to assess the combined effect on cell behaviour

Surface topography and surface chemistry can influence cell adhesion. This study evaluated how the combined effect of topography and chemistry can reduce cell spreading and proliferation. Silica nanoparticulate coatings ranging from 7, 14 and 21 nm in diameter were manufactured on glass substrates and chemically modified using organofunctional siloxanes bearing methyl (−CH3), sulphydryl (−SH), amine (−NH2), carboxyl (−COOH) and hydroxyl (−OH) terminal functional groups. Chemical modification of 7 nm silica induced changes in wettability with the advancing angle increasing for all modifications and the receding angle increasing for −CH3, −NH2 and −SH group modifications. X-ray Photoelectron Spectroscopy (XPS) revealed that the surface chemistry was altered for all chemically modified surfaces confirming the modification step. The Field Emission Scanning Electron Microscopy (FESEM) demonstrated that the nanoparticulate coating remained intact after each chemical treatment. Optical microscopy from tissue culture experiments revealed changes in the morphology of the cells that could be attributed to the surface topography of the nanoparticulate coatings irrespective of the surface chemistry.

TOF-SIMS Analysis of a 576 Micropatterned Copolymer Array To Reveal Surface Moieties That Control Wettability

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used in a high-throughput fashion to obtain mass spectra from the surfaces of 576 novel acrylate-based polymers, synthesized using a combinatorial approach and in a micropatterned format. To identify variations in surface chemistry within the library, principal component analysis (PCA) was used. PCA clearly identified surface chemical commonality and differences within the library. The TOF-SIMS spectra were also used to determine the relationship between water contact angle (WCA) and the surface chemistry of the polymer library using partial least-squares regression (PLS). A good correlation between the TOF-SIMS data from the novel polymers and water contact angle was obtained. Examination of the PLS regression vector allowed surface moieties that correlate with high and low WCA to be identified. This in turn provided an insight into molecular structures that significantly influence wettability. This study demonstrates that multivariate analysis can be successfully applied to TOF-SIMS data from a large library of samples and highlights the potential of these techniques for building complex surface property/chemistry models.

X-ray Photoelectron Spectroscopic Study of the Surface State during Ethane Oxidative Dehydrogenation at Millisecond Contact Times

The chemical nature of Pt/α-Al2O3 catalysts has been studied using X-ray photoelectron spectroscopy (XPS) during catalyst preparation and after being exposed to different feed compositions during autothermal oxidative dehydrogenation of ethane. In addition, the axial variation in surface chemistry has been probed by studying the front and back sides of the catalyst. Significant surface changes were observed following the addition and removal of chlorine to the feed. Chlorine addition led to large carbon deposits throughout the catalyst, and a significant surface concentration of chlorine on the catalyst surface. Chlorine addition also changed the oxidation state of platinum, leading to more oxidized platinum at the front of the monolith and more reduced platinum at the back of the monolith. Subsequent removal of chlorine led to the disappearance of chlorine from the XPS spectrum and to the removal of a significant amount of carbon from the front and back of the catalytic monolith.

Affinity chromatography using biocompatible and reusable biotinylated membranes

A novel, reusable biotinylated affinity chromatography strategy for the bio-specific binding of bioactive avidin tagged enzymes or polypeptides is reported. Using an avidin coupled peroxidase fusion protein as a test system; non-specific protein shielding and matrix regeneration were also shown. The amphiphilic surfactant Pluronic ® F108 was used as an affinity linker, by non-covalent binding to membrane chromatographic matrices while the terminal hydroxyl groups of Pluronic were covalently coupled to the biological ligand biotin. Planar nonporous membranes of varying surface chemistry were synthesised to test the matrix dependent affinity binding of biotinylated Pluronic and their respective ability to resist non-specific protein adsorption. Membrane regeneration using sodium dodecyl sulphate (SDS) was capable of displacing both adsorbed proteins and Pluronic. SDS micelles (34 mM) were effective in desorbing membrane bound protein while 5 mM SDS removed up to 85% of the bound ligand after 20 h incubation at 20 °C. In this study, polyvinylidene membranes had the highest ligand binding capacity of 0.22 mg cm −2 and specific, competitive affinity binding of avidin-peroxidase was shown in the presence of up to 0.2 mg ml −1 ‘contaminant’ proteins. The resultant biocompatible affinity chromatographic system was regenerated and reused with no significant change in performance for up to five cycles.

Influence of substratum surface chemistry/energy and topography on the human fetal osteoblastic cell line hFOB 1.19: Phenotypic and genotypic responses observed in vitro

Time-dependent phenotypic response of a model osteoblast cell line (hFOB 1.19, ATCC, and CRL-11372) to substrata with varying surface chemistry and topography is reviewed within the context of extant cell-adhesion theory. Cell-attachment and proliferation kinetics are compared using morphology as a leading indicator of cell phenotype. Expression of ( α 2, α 3, α 4, α 5, α v, β 1, and β 3) integrins, vinculin, as well as secretion of osteopontin (OP) and type I collagen (Col I) supplement this visual assessment of hFOB growth. It is concluded that significant cell-adhesion events—contact, attachment, spreading, and proliferation—are similar on all surfaces, independent of substratum surface chemistry/energy. However, this sequence of events is significantly delayed and attenuated on hydrophobic (poorly water-wettable) surfaces exhibiting characteristically low-attachment efficiency and long induction periods before cells engage in an exponential-growth phase. Results suggest that a ‘time–cell–substratum–compatibility–superposition principle’ is at work wherein similar bioadhesive outcomes can be ultimately achieved on all surface types with varying hydrophilicity, but the time required to arrive at this outcome increases with decreasing cell–substratum–compatibility. Genomic and proteomic tools offer unprecedented opportunity to directly measure changes in the cellular machinery that lead to observed cell responses to different materials. But for the purpose of measuring structure–property relationships that can guide biomaterial development, genomic/proteomic tools should be applied early in the adhesion/spreading process before cells have an opportunity to significantly remodel the cell–substratum interface, effectively erasing cause and effect relationships between cell–substratum–compatibility and substratum properties. Impact Statement This review quantifies relationships among cell phenotype, substratum surface chemistry/energy, topography, and cell–substratum contact time for the model osteoblast cell line hFOB 1.19, revealing that genomic/proteomic tools are most useful in the pursuit of understanding cell adhesion if applied early in the adhesion/spreading process.

A Study of the Effects of Surface Chemistry on the Initial Deposition Mechanisms of Dairy Fouling

The initial interactions between milk protein components and surfaces with varying surface chemistry are the main focus of this study. The research draws from the expectation that suitable modification of heating surfaces may minimise the effects of protein fouling and/or decrease the deposit adhesion strength to facilitate simpler cleaning procedures. Samples to be fouled were placed in a flow-through rig, and whey protein fouling solutions were pumped through the rig to flow past the samples. Fouling times were kept under 3 min in order to study the deposit forming during the initial stages at elevated temperatures. Whey protein deposits were formed on stainless steel and diamond-like carbon (DLC) coated stainless steel surfaces. Compositional analysis of the deposit formed on the surfaces was performed using X-ray photoelectron spectroscopy (XPS). Possible protein functional groups were identified by analysing the C, O and N components on the surface. Angle resolved XPS allowed determination of groups which may be involved in bonding. Preliminary results suggest bonding on Si-doped DLC involves N containing groups and C—OH groups. Similar analyses are being performed for stainless steel and standard DLC surfaces. These initial results will be further verified and accompanied by measurement of deposit weight and removal characteristics to better determine the effect of modification.

The significance of electrokinetic characterization for interpreting interfacial phenomena at planar, macroscopic interfaces

Streaming potential measurements provide valuable information for the validation and interpretation of interfacial phenomena that occur at flat macroscopic surfaces. Planar substrates have been extensively used for the interpretation of events, which occur at particulate surfaces; however, these flat surfaces are often only questionably representative of their particulate counterparts due to variations in surface chemistry and topography. In this study, the zeta potential from planar macroscopic surfaces of PMMA, mica, graphite, fluorite, and calcite have been calculated from streaming potentials measured in aqueous solutions using an asymmetric clamping cell. These zeta potentials have been found to significantly contribute to understanding and interpretation of interfacial phenomena influenced by Coulombic interactions including adsorption, surface forces, and the structure of surface micelles.

AuPd Metal Nanoparticles as Probes of Nanoscale Thermal Transport in Aqueous Solution

Water- and alcohol-soluble AuPd nanoparticles have been investigated to determine the effect of the organic stabilizing group on the thermal conductance G of the particle/fluid interface. The thermal decays of tiopronin-stabilized 3−5-nm diameter AuPd alloy nanoparticles, thioalkylated ethylene glycol-stabilized 3−5-nm diameter AuPd nanoparticles, and cetyltrimethylammonium bromide-stabilized 22-nm diameter Au-core/AuPd-shell nanoparticles give thermal conductances G ≈ 100−300 MW m-2 K-1 for the particle/water interfaces, approximately an order of magnitude larger than the conductance of the interfaces between alkanethiol-terminated AuPd nanoparticles and toluene. The similar values of G for particles ranging in size from 3 to 24 nm with widely varying surface chemistry indicate that the thermal coupling between AuPd nanoparticles and water is strong regardless of the self-assembled stabilizing group.

Polymeric coatings for biomedical devices

To improve the properties of materials in biomedical applications and to allow a better interaction of the medical device with the biological system surrounding it, frequently polymeric coatings are applied. However, the adhesion of the coating to the substrate usually poses a problem as the materials involved have either rather inert surfaces or strongly varying surface chemistries. We describe a new approach which allows to attach a wide variety of polymer films to organic substrates either of polymeric or biological origin. The technique is based on photochemical processes occurring in benzophenone group containing polymers, which lead to simultaneous crosslinking of the polymer in the coating and surface-attachment of the forming polymer network. The synthesis and characterization of monolayers and surface-attached polymer networks through this route are described and possible applications of this approach in the biomedical area are discussed.

Sulfur adsorption at GaAs(1 0 0) from solution: role of the solvent in surface chemistry

The chemistry of GaAs(1 0 0) oxide-free surfaces treated with solutions of ammonium sulfide in different amphiprotic solvents (water, alcohols) was studied by photoemission spectroscopy in order to clarify the role, which the solvent plays in adsorbate interaction with the surface atoms at the semiconductor/solution interface. Adsorption of sulfur from solution results in the appearance of As–S bonds with solvent-dependent chemical shifts vs. the As–Ga bulk emission. Bonds with larger chemical shifts are formed in low dielectric constant alcohols. Annealing of the surfaces results in the decomposition of As–S bonds and the appearance of Ga–S bonds. At the surfaces treated with high dielectric constant solutions (water- or methanol-based) elemental arsenic appears after As–S decomposition. At the surfaces formed in the solutions with low dielectric constant (isopropanol- or tert-butanol-based) the formation of new Ga–S species with annealing is accompanied by a decrease in the As–S chemical shift. Further annealing of the surface causes the disappearance of As–S bonds and the appearance of As–As surface dimers. Valence band spectra of GaAs(1 0 0) surfaces after annealing contain a solvent-dependent Ga–S related valence state. The observed variation of surface chemistry with change of sulfide solution is related to the variation of the adatom reactivity by different solvation shells.

Sizings on Alkali-Resistant Glass Fibers: Environmental Effects on Mechanical Properties

The alkali-resistant glass fibers (ARG) are coated with special sizings to provide superior alkali resistance and are designed to reinforce cementitious and other alkali matrixes. The assessment of changes in the fiber surface nanomechanical properties is essential for understanding the fiber bulk mechanical fracture behavior. Here we present examples demonstrating sensitive surface stiffness and dissipated energy with regard to the depth profile at the nanoscale, using atomic force microscopy with nanoindentation. A nondimensional energy index is proposed to estimate inhomogeneous surface properties and account for the substrate effect. Additionally, the variations in surface chemistry were evaluated by Fourier transform infrared attenuated total reflection spectroscopy and thermal gravimetric analysis. Among three types of aqueous environments evaluated, an alkaline solution is the most aggressive to the fiber surface. Subsequently, we describe the effect of surface property variability on the fiber ten...

Rheology, Sedimentation, and Filtration of TiO2 Suspensions

AbstractIt is shown that with aqueous suspensions of colloidal oxide and hydroxide particles simple rheometric and sedimentation experiments allow the determination of the optimum pH for filtration and washing. This approach is more practical than zeta potential measurements, as explained by a theoretical review and illustrated by experiments with industrial TiO2 white pigments of varying surface chemistry. Besides, the solids content of the filter cake and its dependence on pH is correctly predicted from the rheology of the suspension, thus giving an idea of the mechanism of filter cake formation. This follows from a comparison to the results of filtration experiments. There, the influences of filter vacuum as well as of pH and solids content of the pigment feed suspension on filtration capacity and washing efficiency have been studied. The experiments also illustrate an inexpensive method of how to find the optimum set of parameters for an economical drum filter operation in the plant.

Characterization of non-uniform wettability on flame-treated polypropylene-film surfaces

The flame treatment of polypropylene (PP) film involves the use of impinging, conical flames to oxidize the surface of the PP.Depending on treatment conditions, the PP film can be exposed to an inhomogeneous environment because of the conical shape of the flames. This environment can lead to cross-web variations, or 'lanes', in the wettability of the film. We have developed a simple method to quantify these non-uniformities using the information provided by the Wilhelmy plate technique of dynamic contact angle measurement. Both surface-averaged and spatially resolved surface-energy data can be obtained by this technique. In the case of our PP film, the spatial nonuniformities were found to be caused by variations in surface chemistry, not topography. These nonuniformities are not observed on untreated PP. Use of this method enables a quantitative evaluation of the effects of flame-treatment process variables on treatment uniformity.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) for high-throughput characterization of biosurfaces

A graded oxidation process, involving UV-ozone (UVO) treatment, was used to create a poly(ε-caprolactone) (PCL) surface with a systematic variation in surface chemistry. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has proved useful in characterizing the chemical composition of these surfaces and in monitoring the oxidation process. The TOF-SIMS data correlates with contact angle data and the results of the binding studies performed with mouse calvarial cells. UVO treatment resulted in a PCL surface with improved wettability and cellular adhesion.