Immobilization of tetraphenylporphyn and its metallocomplexes on the surface of plasma-treated polypropylene

The immobilization of 5,10,15,20-tetraphenylporphyn and its zinc and manganese complexes on the surface of polypropylene modified by plasmachemical treatment and subsequent grafting copolymerization of acrylamide or 4-vinylpyridine has been studied by multiple attenuated total reflection FTIR spectroscopy, electronic absorption spectroscopy, and atomic force microscopy. It has been demonstrated that the immobilized molecules of tetraphenylporphyn and its metallocomplexes are active in the photosensitized generation of singlet oxygen to the gas phase.     

Photoluminescence of TiO2: effect of UV light and adsorbed molecules on surface band structure

The photoluminescence (PL) of TiO(2) at 529.5 nm (2.34 eV) has been found to be a sensitive indicator of UV-induced band structure modification. As UV irradiation occurs, the positive surface potential changes and shifts the depth of the depletion layer. In addition, reversible band bending due to the adsorption of the electron-donor NH(3) and CO molecules has been observed in measurements combining PL with FTIR surface spectroscopy. It has been found that the O(2) molecule acts in two ways: as a reversibly adsorbed electron-acceptor molecule and as an irreversibly adsorbed molecule that heals natural oxygen vacancy defects in the near-surface region.     

Production of highly homogeneous Si(100) surfaces by H2O etching: surface morphology and the role of strain

The etching of Si(100) surfaces in ultrapure water was studied with a combination of infrared spectroscopy (FTIR) and scanning tunneling microscopy (STM). While the FTIR results show that the initially rough H/Si(100) surface becomes highly homogeneous during etching, a phenomenon generally associated with surface smoothing, STM images reveal that the homogeneity is associated with the formation of well-defined etch hillocks. After many hours of etching, the resulting H-terminated surface is composed of stripes of atomically flat Si(100) terminated by etch hillocks bounded by {111}- and {110}-oriented microfacets. Polarization analysis of the Si-H stretching modes provides strong evidence for uniform dihydride-termination of the flat regions, with the narrow (approximately 25 A) width of these stripes allowing for relaxation of steric strain between neighboring dihydrides. The unusual hill-and-valley etch morphology is attributed to the effects of steric strain on the reactivity of sites on the etched surface.     

Analytical strategies for characterizing the surface chemistry of nanoparticles

Chemical modifications of nanoparticle (NP) surfaces are likely to regulate their activities, remove their toxic effects, and enable them to perform desired functions. It is urgent to develop analytical strategies for acquiring structural and quantitative information about small molecules linked to the surface of NP. Recent progress in characterizing the surface chemistry of NPs using nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, liquid chromatography–mass spectroscopy (LC–MS), X-ray photoelectron spectroscopy (XPS), and combustion elemental analysis are reviewed.     

Organic surface modification and analysis of titania nanoparticles for self-assembly in multiple layers

The characteristics of TiO₂ coatings can greatly influence their final performance in large-scale applications. In the present study, self-assembly of TiO₂ nanoparticles (NPs) in multiple layers was selected as a deposition procedure on various substrates. For this, the main prerequisite constitutes the surface modification of both NPs and substrate with, for example, silane coupling agents. A set of functionalized TiO₂ NPs has been produced by reaction with either (3-aminopropyl)triethoxysilane (APTES) or (3-aminopropyl)phosphonic acid (APPA) to functionalize the NP surface with free amino-groups. Then, the complementary functionalized NP set can be obtained from an aliquot of the first one, through the conversion of free surface amino groups to aldehydes by reaction with glutaraldehyde (GA). Several types of TiO₂ NPs differing in size, shape, and specific surface area have been functionalized. Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), SEM/ energy-dispersive X-ray spectroscopy (EDS), XPS, Auger electron spectroscopy (AES), and Time-of-Flight (ToF)-SIMS analyses have been carried out to evaluate the degree of functionalization, all the analytical methods employed demonstrating successful functionalization of TiO₂ NP surface with APTES or APPA and GA.     

Characterization of electron-beam-modified surface coated clay fillers and their influence on physical properties of rubbers

A novel process of surface modification of clay filler has been developed by coating this with an acrylate monomer, trimethylol propane triacrylate (TMPTA) or a silane coupling agent, triethoxy vinyl silane (TEVS) followed by electron beam irradiation. Characterization of these surface modified fillers has been carried out by Fourier-transform infrared analysis (FTIR), electron spectroscopy for chemical analysis (ESCA), wettability by dynamic wicking method measuring the rise of a liquid through a filler-packed capillary tube and water flotation test, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). Presence of the acrylate and the silane coupling agent on the modified fillers has been confirmed from FTIR, ESCA, and EDX studies, which has also been supported by TGA studies. The contact angle measurement by dynamic wicking method suggests improvement in hydrophobicity of the treated fillers, which is supported by water flotation test especially in the case of silanized clay. However, XRD studies demonstrate that the entire modification process does not affect the bulk properties of the fillers. Finally, both unmodified and modified clay fillers have been incorporated in styrene butadiene rubber (SBR) and nitrile rubber (NBR). Rheometric and mechanical properties reveal that there is a definite improvement using these modified fillers specially in the case of silanized clay compared to the control sample, probably due to successful enhancement in interaction between the treated clay and the base polymer.     

Polymorphism behavior of poly(ethylene naphthalate)/clay nanocomposites: role of clay surface modification

The influence of clay surface modification on the polymorphism behavior of poly(ethylene naphthalate) (PEN)/clay nanocomposites was investigated via in situ Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. The results show that untreated clay has a heterogeneous nucleating effect on PEN and favors the beta-crystal form, while the surfactant 1-hexadecyl-2,3-dimethylimidazolium (IMC16) has a plasticization effect and tends to enhance the kinetically favored alpha-phase instead. In contrast, the nanocomposite (PEN/IMC16-MMT) formed from IMC16-treated clay (IMC16-MMT) exhibits a strong temperature-dependent polymorphic behavior, with the beta-phase being more favored at 200 degrees C, but the alpha-phase being preferred instead at 180 degrees C. In situ FTIR spectroscopy of PEN/IMC16-MMT reveals an abrupt change in the concentration of alpha- and beta-"crystalline conformers" between the two temperatures during the induction period of crystallization. This is attributed to the hindered formation of stable nuclei at the organoclay surface. In addition, surfactant degradation gives rise to a highly plasticized polymer/organoclay interface. The combination of the hindered heterogeneous nucleation and plasticization effects gives rise to the unique temperature-dependent polymorphism behavior in PEN/IMC16-MMT.     

Multitechnique surface spectroscopic studies of plasma modified polymers III. H2O and O2/H2O plasma modified poly(methyl methacrylate)s

The surfaces of poly(methyl methacrylate) (PMMA) films modified by O₂H₂O and H₂O radio-frequency glow discharge plasmas were studied using electron spectroscopy for chemical analysis (ESCA or XPS), low energy ion scattering (LEISS or ISS), Fourier transform IR spectroscopy (FTIR) with attenuated total reflectance (ATR) sampling, and critical surface energy from contact angle measurements. The extent and nature of modification with respect to promotion of a hydrophilic surface compared to the hydrophobic surface of the unmodified PMMA has been probed. Results show drastic decreases in C/O ratio at the near surface, which increases to that of the unmodified PMMA as deeper cross sections are analyzed. In addition peak fitting of ESCA data correlated with FTIR functional group information allows for the qualitative and quantitative analysis of the resulting bonding and structure of the modified layer. From these results combined with the polarity and surface energy differences obtained from contact angle measurements, the structural changes are discussed with respect to plasma reaction mechanisms and differences in the structure of the modified polymer films.     

Effect of surface coverage on the conformation and mobility of C18-modified silica gels

C18-modified silica gels with surface coverages of 2 to 8.2 micromol m(-2), were prepared by different synthetic pathways and characterized by Fourier Transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR) spectroscopy, and chromatographic measurements. The effects of temperature and bonding density on the conformational order of C18-modified silica gels were studied in detail by FTIR spectroscopy. The silane functionality and degree of cross-linking of silane ligands on the silica surface were evaluated by 29Si cross-polarization magic-angle spinning (CP/MAS) NMR and the structural order and mobility of the alkyl chains were investigated by 13C CP/MAS NMR spectroscopy. CH2 symmetric and anti-symmetric stretching bands and CH2 wagging bands were used as IR probes to monitor the conformational order and flexibility of the alkyl chains in the C18 phases. Qualitative information about the conformational order was obtained from frequency shifts of the CH2 symmetric and anti-symmetric stretching bands. The relative amounts of kink/gauche-trans-gauche, double-gauche, and end-gauche conformers in the alkyl chains were determined by analysis of CH2 wagging bands. These results indicate that surface coverage plays a dominant role in the conformational order of C18-modified silica gels. The FTIR and NMR data are discussed in the context of the chromatographic shape-selectivity differences.     

Novel multiparametric approach to elucidate the surface amine-silanization reaction profile on fluorescent silica nanoparticles

This Article addresses the important issue of the characterization of surface functional groups for optical bioassay applications. We use a model system consisting of spherical dye-doped silica nanoparticles (NPs) that have been functionalized with amine groups whereby the encapsulated cyanine-based near-infrared dye fluorescence acts as a probe of the NP surface environment. This facilitates the identification of the optimum deposition parameters for the formation of a stable ordered amine monolayer and also elucidates the functionalization profile of the amine-silanization process. Specifically, we use a novel approach where the techniques of fluorescence correlation spectroscopy (FCS) and fluorescence lifetime measurement (FL) are used in conjunction with the more conventional analytical techniques of zeta potential measurement and Fourier transfer infrared spectroscopy (FTIR). The dynamics of the ordering of the amine layer in different stages of the reaction have been characterized by FTIR, FL, and FCS. The results indicate an optimum reaction time for the formation of a stable amine layer, which is optimized for further biomolecular conjugation, whereas extended reaction times lead to a disordered cross-linked layer. The results have been validated using an immunoglobulin (IgG) plate-based direct binding assay where the maximum number of IgG-conjugated aminated NPs were captured by immobilized anti-IgG antibodies for the NP sample corresponding to the optimized amine-silanization condition. Importantly, these results point to the potential of FCS and FL as useful analytical tools in diverse fields such as characterization of surface functionalization.     

Grafting cavitands on the Si(100) surface

Cavitand molecules having double bond terminated alkyl chains and different bridging groups at the upper rim have been grafted on H-terminated Si(100) surface via photochemical hydrosilylation of the double bonds. Pure and mixed monolayers have been obtained from mesitylene solutions of either pure cavitand or cavitand/1-octene mixtures. Angle resolved high-resolution X-ray photoelectron spectroscopy has been used as the main tool for the monolayer characterization. The cavitand decorated surface consists of Si-C bonded layers with the upper rim at the top of the layer. Grafting of pure cavitands leads to not-well-packed layers, which are not able to efficiently passivate the Si(100) surface. By contrast, monolayers obtained from cavitand/1-octene mixtures consist of well-packed layers since they prevent silicon oxidation after aging. AFM measurements showed that these monolayers have a structured topography, with objects protruding from the Si(100) surface with average heights compatible with the expected ones for cavitand molecules.     

Characterization of the cell surface and cell wall chemistry of drinking water bacteria by combining XPS, FTIR spectroscopy, modeling, and potentiometric titrations

Aquabacterium commune, a predominant member of European drinking water biofilms, was chosen as a model bacterium to study the role of functional groups on the cell surface that control the changes in the chemical cell surface properties in aqueous electrolyte solutions at different pH values. Cell surface properties of A. commune were examined by potentiometric titrations, modeling, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. By combining FTIR data at different pH values and potentiometric titration data with thermodynamic model optimization, the presence, concentration, and changes of organic functional groups on the cell surface (e.g., carboxyl, phosphoryl, and amine groups) were inferred. The pH of zero proton charge, pH(zpc) = 3.7, found from titrations of A. commune at different electrolyte concentrations and resulting from equilibrium speciation calculations suggests that the net surface charge is negative at drinking water pH in the absence of other charge determining ions. In situ FTIR was used to describe and monitor chemical interactions between bacteria and liquid solutions at different pH in real time. XPS analysis was performed to quantify the elemental surface composition, to assess the local chemical environment of carbon and oxygen at the cell wall, and to calculate the overall concentrations of polysaccharides, peptides, and hydrocarbon compounds of the cell surface. Thermodynamic parameters for proton adsorption are compared with parameters for other gram-negative bacteria. This work shows how the combination of potentiometric titrations, modeling, XPS, and FTIR spectroscopy allows a more comprehensive characterization of bacterial cell surfaces and cell wall reactivity as the initial step to understand the fundamental mechanisms involved in bacterial adhesion to solid surfaces and transport in aqueous systems.     

Manipulation of electrocatalytic reaction pathways through surface chemistry: in situ Fourier transform infrared spectroscopic studies of 1,3-butanediol oxidation on a Pt surface modified with Sb and S adatoms

Cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroscopy were employed to study the electrocatalytic properties of a Pt electrode modified with adatoms of antimony (Sb) or sulfur (S) for 1,3-butanediol (1,3-BD) oxidation. The results demonstrated the possibility of manipulating the reaction pathways involved in 1,3-BD oxidation through chemical modification of the Pt electrode surface. Both Sb and S adatoms (Sb(ad) and S(ad)) can inhibit the dissociative reaction of 1,3-BD into CO, which is the main source of self-poisoning in electrocatalysis of small organic molecules. On Pt electrodes modified with a high coverage of Sb(ad) (Pt/Sb(ad)) the onset oxidation potential of 1,3-BD has been significantly decreased, which is attributed to the fact that the oxidation of Sb(ad) occurs at lower potentials than that of the Pt surface. In situ FTIR results illustrated that, although at potentials below 0.5 V (vs a saturated calomel electrode), at which the Sb(ad) is stable on the Pt electrode surface, both carbonyl and CO2 species have been observed, the principal oxidation products of 1,3-BD are carbonyl species. Such results indicate that the reaction is mainly the dehydrogenation of 1,3-BD molecules. However, at potentials above 0.5 V the proportion of CO2 species in the oxidation products increases quickly, implying that the reaction has turned to the breakage of C-C bonds in 1,3-BD molecules and the subsequent oxidation of the cleaved fragments. In contrast with the cases of 1,3-BD oxidation on Pt and Pt/Sb(ad) electrodes, the reaction of 1,3-BD oxidation on a Pt electrode modified with S adatoms (Pt/S(ad)) is oriented completely to the production of carbonyl species when electrode potentials are below 0.9 V, though the reaction activity is relatively low. When the electrode potential is increased above 0.9 V, the intensity of the CO2 IR band in the FTIR spectra increases rapidly, corresponding to a fast oxidation of 1,3-BD on surface Pt sites recovered by the oxidation and desorption of S(ad) from the Pt surface.     

Structural analysis of the reconstructed Si(001)-C surface

The atomic structure of reconstructed Si(001)c(4 x 4)-C surface has been studied by coaxial impact collision ion scattering spectroscopy. When the 100L of ethylene (C(2)H(4)) molecules have been exposed on Si(001)-(2 x 1) surface at 700 degrees C, it is found that C atoms cause the ordering of missing Si dimer defects and occupy the fourth layer of Si(001) directly below the bridge site. Our results provide the support for the previous model in which a missing dimer structure is accompanied by C incorporation into the subsurface.     

Influence of phosphonation and phosphation on surface acid-base and morphological properties of CaO as investigated by in situ FTIR spectroscopy and electron microscopy

Pure, phosphated, and phosphonated CaO samples were prepared and characterized by X-ray powder diffractometry, FTIR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray microprobing. Surface acid-base properties were probed by in situ FTIR spectroscopy of adsorbed CO (at 85 K), CDCl3 (at RT), CO2 (at RT), and methyl butynol decomposition reactions (at 473 K). Results obtained have shown phosphate and, to a larger extent, phosphonate additives to enhance the strength of Lewis acid sites exposed on CaO surfaces, at the expense of the Lewis base site strength. The phosphonation has been found, moreover, to make CaO particles grow in a preferential direction and be less susceptible to rehydration. These findings may establish surface chemical attributes for the application of the methylene bisphosphonate (MBP) class of drugs to hamper acid-induced resorption of bone materials (osteoporosis).     

Methanol adsorption on the beta-Ga2O3 surface with oxygen vacancies: theoretical and experimental approach

Methanol adsorption on beta-Ga2O3 surface has been studied by Fourier transform infrared spectroscopy (FTIR) and by means of density functional theory (DFT) cluster model calculations. Adsorption sites of tetrahedral and octahedral gallium ions with different numbers of oxygen vacancies have been compared. The electronic properties of the adsorbed molecules have been monitored by computing adsorption energies, optimized geometry parameters, overlap populations, atomic charges, and vibrational frequencies. The gallia-methanol interaction has different behaviors according to the local surface chemical composition. The calculations show that methanol can react in three different ways with the gallia surface giving rise to a nondissociative adsorption, a dissociative adsorption, and an oxidative decomposition. The surface without oxygen vacancies is very reactive and produces the methanol molecule decomposition. The molecule is nondissociatively adsorbed by means of a hydrogen bond between the alcoholic hydrogen atom and a surface oxygen atom and a bond between the alcoholic oxygen atom and a surface gallium atom. Two neighbor oxygen vacancies on tetrahedral gallium sites produce the dissociation of the methanol molecule and the formation of a bridge bond between two surface gallium atoms and the methoxy group.     

Grafting of polyethylene glycols onto nanometer silica surface by 1,4‐phenylene diisocyanate

In this paper, polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica in toluene by using 1,4‐phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one‐step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate‐bound silica with PEG. The PEG‐grafted silica has been characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and SEM analyses. The effects of reaction time, temperature and molar ratio of reactant on the effectiveness of the surface grafting were also investigated. Optimum grafting conditions of PEG were obtained at the temperature of 80 °C for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA. Copyright © 2010 John Wiley & Sons, Ltd.     

Photolabile carboxylic acid protected terpolymers for surface patterning. Part 2: Photocleavage and film patterning

The surface properties of films made of p-methoxyphenacyl derivative terpolymers, associated with photocleavage by UV irradiation, and their optical patterning are investigated. The deprotection reaction has been monitored by UV and FTIR spectroscopy, contact angle measurements, and X-ray photoelectron spectroscopy, revealing the photoremoval of the protecting p-methoxyphenacyl group in high yields under mild conditions. Parallel and serial patterning of the films has been performed by selective irradiation through optical masks and by laser irradiation via fiber tips of a scanning near-field optical microscope, respectively. By irradiation of photolabile protected functional groups, free carboxylic groups become exposed to the surface with which fluorescent dyes and proteins can be associated specifically.     

Effects of surface morphology on the anchoring and electrooptical dynamics of confined nanoscale liquid crystalline films

The orientation and dynamics of two 40-nm thick films of 4-n-pentyl-4'-cyanobiphenyl (5CB), a nematic liquid crystal, have been studied using step-scan Fourier transform infrared spectroscopy (FTIR). The films are confined in nanocavities bounded by an interdigitated electrode array (IDA) patterned on a zinc selenide (ZnSe) substrate. The effects of the ZnSe surface morphology (specifically, two variations of nanometer-scale corrugations obtained by mechanical polishing) on the initial ordering and reorientation dynamics of the electric-field-induced Freedericksz transition are presented here. The interaction of the 5CB with ZnSe surfaces bearing a spicular corrugation induces a homeotropic (surface normal) alignment of the film confined in the cavity. Alternately, when ZnSe is polished to generate fine grooves along the surface, a planar alignment is promoted in the liquid crystalline film. Time-resolved FTIR studies that enable the direct measurement of the rate constants for the electric-field-induced orientation and thermal relaxation reveal that the dynamic transitions of the two film structures are significantly different. These measurements quantitatively demonstrate the strong effects of surface morphology on the anchoring, order, and dynamics of liquid crystalline thin films.     

Plasma-Induced Graft Polymerization of Poly(ethylene glycol) Methyl Ether Methacrylate on Si(100) Surfaces for Reduction in Protein Adsorption and Platelet Adhesion

Argon plasma-induced graft polymerization of a solution-coated macromonomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), on the Si(100) surface was carried out to impart anti-fouling properties to the Si(100) surface. The surface composition and microstructure of the PEGMA graft-polymerized Si(100) surfaces were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) measurements. The extent of crosslinking in the plasma-graft polymerized PEGMA (pp-PEGMA) was estimated by gel fraction determination. In general, an appropriate RF power of about 15 W and a PEGMA macromonomer concentration of about 1 wt% in the coating solution for plasma polymerization produced a high graft yield of pp-PEGMA on the Si(100) surface (the pp-PEGMA-g-Si surface). The Si(100) surface with a high concentration of the grafted pp-PEGMA was effective in preventing bovine serum albumin (BSA) adsorption and platelet adhesion.