Protein resistant polyurethane surfaces by chemical grafting of PEO: amino-terminated PEO as grafting reagent

The objective of this work was to gain a better understanding of the mechanism of resistance to protein adsorption of surfaces grafted with poly(ethylene oxide) (PEO). A polyurethane-urea was used as a substrate to which PEO was grafted. Grafting was carried out by introducing isocyanate groups into the surface followed by reaction with amino-terminated PEO. Surfaces grafted with PEO of various chain lengths (PUU-NPEO) were prepared and characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). XPS data indicated higher graft densities on the PUU-NPEO surfaces than on analogous surfaces prepared using hydroxy-PEO (PUU-OPEO) as reported previously [J.G. Archambault, J.L. Brash, Colloids Surf. B: Biointerf. 33 (2004) 111-120]. Protein adsorption experiments using radiolabeled myoglobin, concanavalin A, albumin, fibrinogen and ferritin as single proteins in buffer showed that adsorption was reduced on the PEO-grafted surfaces by up to 95% compared to the control. Adsorption decreased with increasing PEO chain length and reached a minimum at a PEO MW of 2000. Adsorption levels on surfaces with 5000 and 2000 MW grafts were similar. There was no clear effect of protein size on resistance to protein adsorption. Adsorption on the PUU-NPEO surfaces was significantly lower than on the corresponding PUU-OPEO surfaces, again suggesting higher graft densities on the former. Adsorption of fibrinogen from plasma was also greatly reduced on the grafted surfaces. From analysis (SDS-PAGE, immunoblotting) of the proteins eluted after plasma exposure, it was found that the grafted surfaces and the unmodified substrate adsorbed the same proteins in roughly the same proportions, suggesting that adsorption to the PEO surfaces occurs on patches of bare substrate. The PEO grafts did not apparently cause differential access to the substrate based on protein size.     

Preparation of thin SnO2 layers by inorganic sol-gel process

SnO₂ sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl₄, (2) washing the precipitates with NH₄NO₃ solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO₃, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO₂ by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared.     

Preparation of thin stable erbium target sandwiched between carbon layers

Targets of isotopically enriched ¹⁷⁰Er (erbium) were prepared on 45 μg/cm² carbon backing using the method of vacuum evaporation. Another layer of carbon with thickness 23 μg/cm² was deposited on it as a protective cap with the help of an electron gun. Carbon backing, Er and the capping carbon layer were deposited using resistive heating and electron gun deposition without disturbing the vacuum. The thickness of ¹⁷⁰Er was measured by X-ray fluorescence analysis as well as with Rutherford backscattering spectrometry and it was found to be 150 μg/cm². Successful preparation of sandwiched targets was very sensitive to substrate temperature, deposition rate, duration of in situ annealing, cooling rate etc.     

A study of thin surface layers by multilayer Mössbauer spectroscopy /MMS/

A stacking Mössbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the⁵⁷Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the⁵⁷Fe film after corrosion in a zinc phosphate solution.     

Grain boundary corrosion of the surface of annealed thin layers of gold by OH· radicals

Annealed thin layers of gold with large mono-crystalline areas were treated with OH^· radicals generated in an electrochemical Fenton reaction. The morphological changes observed with ex situ atomic force microscopy in non-contact mode and grazing incidence X-ray diffractometry show that the grain boundaries, and generally the non-{111} planes, are the loci of highest reactivity, i.e., the places where the gold dissolution is much faster than on the {111} planes.     

Preparation of ultrathin coating layers using surface modified silica nanoparticles

Silica nanoparticles are used in various applications including catalysts, paints and coatings. To reach an optimal performance via stability and functionality, in most cases, the surface properties of the particles are altered using complex procedures. Here we describe a simple method for surface modification of silica nanoparticles (SNP) using sequential adsorption of oppositely charged components. First, the SNPs were made cationic by adsorption of a cationic polyelectrolyte. Poly(allylamine hydrochloride) (PAH) and polyethyleneimine (PEI) were chosen as polycations to investigate the difference between a linear and a branched polyelectrolyte. Next, the dispersion of cationic SNPs was combined with an anionic alkyl ketene dimer (AKD) emulsion. Using this approach cationic, hydrophobic silica particle dispersions were produced. Dynamic light scattering, contact angle measurements and atomic force microscopy (AFM) were used for analyzing the particle and coating layer properties. The chosen polyelectrolyte affected the structure of the dispersion. The layer build-up was studied in detail using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption and layer properties of the cationic polyelectrolytes adsorbed on silica as well as the affinity of AKD to this layer were explored. The application possibilities of the modified particle dispersions were demonstrated by preparing paper and silica surfaces with tailored properties, such as elevated surface hydrophobicity, using an ultrathin coating layer.     

Preparation of thin films of platinum group metals by pulsed MOCVD. II. Deposition of Ru layers

In situ high-temperature mass spectrometry is used to analyze the thermal decomposition of Ru(acac)₃ and Ru(nbd)(allyl)₂ vapor and possible schemes of thermal transformations on the heated surface. By pulsed MOCVD with in situ mass spectrometric control of deposition processes ultrathin Ru layers with a thickness of several nanometers are obtained. The role of the reaction medium, precursor nature, and deposition temperature in the formation of a nanocrystalline structure of the films is revealed. Ruthenium films with a compact continuous structure are formed from Ru(acac)₃ and hydrogen at a deposition temperature of 340°C and below; an increase in the temperature results in the growth of nanogranular Ru layers. Regardless of deposition conditions, from Ru(nbd)(allyl)₂ granular nanocrystalline Ru layers are formed     

Preparation of thin films of platinum group metals by pulsed MOCVD. I. Deposition of Ir layers

Pulsed MOCVD with the in situ mass spectrometric control of the deposition process is employed to obtain ultrathin Ir layers with a thickness from units to tens of nanometers. The role of the reaction medium, precursor nature, and deposition temperature in the formation of the nanocrystalline structure of films is revealed. The deposition of Ir from Ir(acac)₃ in the oxygen atmosphere results in the formation of dense homogeneous structures, while in vacuum or in the hydrogen atmosphere, nanosized granular Ir layers are deposited. When Ir(CO)₂(acac) is used, Ir films with a granular structure are obtained regardless of the reaction medium.     

Analysis of thin layers by means of spark-source mass spectrometry

Summary A device has been constructed with which the surface of a specimen can be scanned with a spark drawn from a fixed counter electrode. The mean depth of penetration is of the order of microns and limits of detection of 0.1 ppm are possible. Repeated scanning allows profile analysis, too.

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Analyse dünner Schichten mit Hilfe der Funken-Massenspektrometrie

Zusammenfassung Eine Anordnung wurde konstruiert, mit der eine sich drehende Probenoberfläche durch eine feste Gegenelektrode abgetastet werden kann. Die mittlere Eindringtiefe pro Funkenentladung liegt in der Größenordnung von Mikrometern. Nachweisgrenzen von 0,1 ppm sind möglich. Durch wiederholtes Abtasten können auch Profilanalysen durchgeführt werden.

     

Highly stable redox-active molecular layers by covalent grafting to conductive diamond

We demonstrate a modular "click"-based functionalization scheme that allows inexpensive conductive diamond samples to serve as an ultrastable platform for surface-tethered electrochemically active molecules stable out to ～1.3 V vs Ag/AgCl. We have cycled surface-tethered Ru(tpy)(2) to this potential more than 1 million times with little or no degradation in propylene carbonate and only slightly reduced stability in water and acetonitrile.     

Oscillations in thin nematic layers

In the present paper a thin nematic liquid crystal layer between two identical boundary surfaces (solid walls or free surfaces in the case of a freely suspended film) is considered. In a mean field approximation it is shown that the interference between the boundary surface-induced smectic density waves results in oscillations of the free energy of the nematic layer and disjoining pressure acting on the boundary surfaces. Theoretical dependence of disjoining pressure on the nematic layer thickness is in qualitative agreement with experiment. Also we have considered a thin film of polar nematic in which in addition to an ordinary monolayer smectic A phase (S_A1) with the layer thickness d equal to the molecular length l the partial bilayer smectic A phase (S_Ad) occurs. It is shown that the variation of the distance between the boundary surfaces can result in the oscillatory S_A1-A_Ad phase transitions in this nematic film     

Water at a hydrophilic solid surface probed by ab initio molecular dynamics: inhomogeneous thin layers of dense fluid

We present a microscopic model of the interface between liquid water and a hydrophilic, solid surface, as obtained from ab initio molecular dynamics simulations. In particular, we focused on the (100) surface of cubic SiC, a leading semiconductor candidate for biocompatible devices. Our results show that in the liquid in contact with the clean substrate, molecular dissociation occurs in a manner unexpectedly similar to that observed in the gas phase. After full hydroxylation takes place, the formation of a thin (approximately 3 A) interfacial layer is observed, which has higher density than bulk water and forms stable hydrogen bonds with the substrate. The presence of this thin layer points at rather weak effects on the structural properties of water induced by a one-dimensional confinement between approximately 1.3 nm hydrophilic substrates. In addition, our results show that the liquid does not uniformly wet the surface, but molecules preferably bind along directions parallel to the Si dimer rows.     

The influence of the surface on conformational equilibrium in thin layers of nematic liquid crystal

Changes in the conformational equilibrium in thin layers of the nematic liquid crystal 5CB between fluorite plates were studied by IR spectroscopy. A decrease in the thickness of the liquid crystalline layer symmetrically confined by poorly wettable fluorite surfaces is accompanied by the shift of conformational equilibrium toward rotamers characterized by a higher energy and the spatial structure preventing dense packing of molecules in the interlayer.     

Structure of water in thin layers

This paper considers the physical behavior of the boundary layers of water near the hydrophilic and hydrophobic surfaces. The overlapping of these layers leads to the generation of structural forces of repulsion, in the first case, and those of attraction, in the second. Inclusion of structural forces in the DLVO theory and the theory of heterocoagulation allows one to explain the results of measurements of contact angles for water solutions at different concentrations, pH values, and temperatures. The maximum influence of structural effects on colloid stability, wetting phenomena, and liquid flow in thin pores is to be expected in two extreme cases—that of a highly lyophobic system and that of a highly lyophilic one.     

Cellulose surface grafting with polycaprolactone by heterogeneous click-chemistry

This work deals with a new approach of grafting cellulose surface fibres by polycaprolactone macromolecular chains in heterogeneous conditions via click-chemistry. Thus, cellulose esters were prepared by reacting Avicel with undecynoic acid, in order to prepare cellulose substrate bearing multiple CC-terminated hairs. The prepared modified Avicel substrates were characterised by FTIR, XPS spectroscopy, elemental analyses and showed that the grafting have indeed occurred. The degree of substitution of the prepared cellulose esters was around 0.1. In parallel, polycaprolactone-diol (PCL) was converted to azido-derivative and the ensuing products characterised by FTIR and ¹³C-NMR spectroscopy. Both methods confirmed the success of such modification. Finally, cellulose esters were reacted with azido-PCL grafts in heterogeneous conditions through “click chemistry”. The thus prepared modified cellulose substrates were characterized by FTIR and XPS spectroscopy as well as elemental analyses. The three techniques confirmed the occurrence of the grafting. A weight gain of 20% was achieved.     

Computer simulations of thin polymer layers

Molecular dynamics calculations are used to explore the structure of dense monolayers of long-chain molecules supported on a planar surface. As a model we consider ensembles of flexible chains consisting of N segments (N=32, 64 and 128) in a box with lateral (x, y) periodicity conditions. The effect of surface coverage on the conformational properties of chains is studied. At high coverages, the results of the simulations show that each chain is strongly stretched along the normal to the surface and the mean layer thickness is linear in N. The segment density distribution along the normal is found to be an universal function A^2/3 f (zA^1/3 N), where A is the surface area per chain. The high-coverage distribution has a well defined broad plateau, in agreement with the so-called blob model. In contrast to the predictions of this model, however, we observe that the chains are strongly stretched at all space scales. Differences between the results of simulations and those predicted by the mean-field theory are also discussed.     

Deposition of thin electroplated Cd-Se layers

Cadmium-selenium alloys were electrodeposited from a sulfuric acid electrolyte. The effect of the H₂SeO₃, CdSO₄, and sulfuric acid concentrations, current density, and temperature on the composition and quality of cathode deposits was studied.