Andrzej Kotarba

Oxygen plasma functionalization of parylene C coating for implants surface : Nanotopography and active sites for drug anchoring

The effect of oxygen plasma treatment (t=0.1-60 min, pO2=0.2 mbar, P=50 W) of parylene C implant surface coating was investigated in order to check its influence on morphology (SEM, AFM observations), chemical composition (XPS analysis), hydrophilicity (contact angle measurements) and biocompatibility (MG-63 cell line and Staphylococcus aureus 24167 DSM adhesion screening). The modification procedure leads to oxygen insertion (up to 20 at.%) into the polymer matrix and together with surface topography changes has a dramatic impact on wettability (change of contact angle from θ=78±2 to θ=33±1.9 for unmodified and 60 min treated sample, respectively). As a result, the hydrophilic surface of modified parylene C promotes MG-63 cells growth and at the same time does not influence S. aureus adhesion. The obtained results clearly show that the plasma treatment of parylene C surface provides suitable polar groups (C=O, C-O, O-C=O, C-O-O and O-C(O)-O) for further development of the coating functionality.

Stability and excitation of potassium promoter in iron catalysts – the role of KFeO2 and KAlO2 phases

Well‐characterized catalyst model compounds of KAlO2 and KFeO2 are investigated by thermal desorption of potassium from the material. The desorbing fluxes of ions, atoms and highly excited states (field ionizable Rydberg states) were studied with surface and field ionization detectors in a vacuum apparatus. From the Arrhenius plots the activation energies for desorption of K and K+ were determined. The chemical state of potassium at the surfaces is concluded to be: ionic on KAlO2 (with the K desorption barrier of 1.76 eV) and covalent on KFeO2 (barrier of 2.73 eV). These results agree with the data obtained earlier for industrial catalysts for ammonia and styrene production. They are interpreted in terms of the Schottky cycle, which is completed for KAlO2 and fails for KFeO2. This failure indicates a non‐equilibrium desorption process. K Rydberg states are only found to desorb from KFeO2, in agreement with the suggestion that such states in some way are responsible for the catalytic activity.

Angular resolved neutral desorption of potassium promoter from surfaces of iron catalysts

Abstract The angular dependence of neutral potassium emission in the form of ground-state atoms as well as Rydberg species is studied from a fused iron catalyst. The catalyst is of the type used for ammonia synthesis in so-called pre-reduced (metallic) condition. The angular distributions observed by surface ionization detection have a more peaked shape than the cosine distribution expected for thermal equilibrium. In the case of a catalyst sample used in the industrial process even a sharp peak on top of a cosine distribution is found. Using detection by field ionization, i.e. detection of Rydberg species only, a rather sharp lobe in the normal direction is found. A theoretical description of cluster formation outside the sample surface from atoms with velocity distributions characteristic for thermal equilibrium is used to interpret the results. The cluster formation is probably due to the long-range interaction between the Rydberg atoms formed on the surface, and the clusters are at least partially formed in an excited state. The cluster sizes contributing to the distributions are estimated from fits to the experimental results. The main cluster size observed with surface ionization detection is concluded to be quite small, containing just a few atoms. There also exist contributions of larger clusters of the size around 10–30 atoms in the case of the pre-reduced catalyst. The used catalyst also gives mainly small clusters, but it does not give clusters of the size 10–30 atoms. Both types of catalyst also give a small number, less than 5%, of very large clusters, with more than 100 atoms according to the model. The field ionization data for the pre-reduced catalyst are well matched by a single cluster size of approximately 30 atoms, which indicates that such clusters have a longer lifetime in the initial excited state than the small clusters.

Emission of excited potassium species from an industrial iron catalyst for ammonia synthesis

The angular dependence of potassium emission-desorption is studied from a fused iron catalyst of the type used for ammonia synthesis. The excited species (K*, Kn*, etc.) and positive ions K+ have strongly different angular distributions. The bilobular distribution measured for ion desorption is concluded to be either due to excited atoms, so-called Rydberg atoms, or excited clusters. Both types of species have to desorb from the edges of the sample and become field ionized and deexcited just outside the sample, as reported in previous studies on an iron oxide catalyst. The peak in the normal direction measured for excited species is due to excited cluster formation outside the catalyst surface. Similarities with previous results for other catalysts are observed. The possibility that the promoter function of potassium in the ammonia synthesis is due to excited species is pointed out.

Sulfur Poisoning of Iron Ammonia Catalyst Probed by Potassium Desorption

The surface of an unpoisoned and sulfur-poisoned industrial iron ammonia catalysts is investigated by K, K+ thermal desorption. The K+ desorption energy increases while the K energy decreases upon poisoning. Presence of sulfur also suppresses the potassium desorption in electronically excited states.

Potassium at catalytic surfaces—stability, electronic promotion and excitation

Thermal desorption of potassium atoms, ions and Rydberg atoms from K-doped transition metal carbides and nitrides were invetigated. The results were rationalized in terms of Schottky cycle. The status of the promoter was evaluated in three aspects: stability at the surface, electronic promotion and non-equilibrium excitation. Their relevance to catalysis is briefly discussed.

Parylene coatings on stainless steel 316L surface for medical applications — Mechanical and protective properties

The mechanical and protective properties of parylene N and C coatings (2-20 μm) on stainless steel 316L implant materials were investigated. The coatings were characterized by scanning electron and confocal microscopes, microindentation and scratch tests, whereas their protective properties were evaluated in terms of quenching metal ion release from stainless steel to simulated body fluid (Hanks solution). The obtained results revealed that for parylene C coatings, the critical load for initial cracks is 3-5 times higher and the total metal ions release is reduced 3 times more efficiently compared to parylene N. It was thus concluded that parylene C exhibits superior mechanical and protective properties for application as a micrometer coating material for stainless steel implants.

Kinetics of activation of the industrial and model fused iron catalysts for ammonia synthesis

Abstract The paper summarizes our results published for many years and also adds new information. Kinetic data concerning the reduction of the oxidized forms of model as well as industrial catalysts used in ammonia synthesis were obtained in dry and in wet atmosphere containing 1% water vapour. The data for the industrial catalyst have been reassessed using three kinetic models. Modifications applied to the classical Seth-Ross model of the shrinking-core type resulted in the best fitting of this equation to the experimental data. The failure of the crackling core model to describe the kinetic data in a quantitative way is tentatively explained. The reduction of model catalysts containing enhanced amounts of wustite and/or potassium proceeds initially linearly with time. The effect of promoters, and especially of potassium, is discussed in more detail. The magnetite-alumina subsystem is responsible for the retardation effect of the water vapour on the reduction rate. A hypothesis is formulated that — in the presence of wustite or potassium — the inhibitive, Al-rich, hydrated surface layer is not effective in hindering the progress of the reduction process.

Energy-pooling transitions to doubly excited K atoms at a promoted iron-oxide catalyst surface: more than 30 eV available for reaction.

The promoter action of alkali atoms, such as K atoms, at heterogeneous catalyst surfaces has been used in industrial catalysis for many decades, giving improved activity and selectivity in the catalyzed chemical reactions. Several mechanisms for this promotion effect have been proposed, among which the Rydberg excitation mechanism is well-supported by experiments from our groups. Further experiments now show that even doubly excited K Rydberg species are formed at an industrial catalyst (styrene catalyst) surface. This indicates that a large excitation energy of >30 eV can easily accumulate in an atomic or molecular species. The methods used for the identification of the excited species are pulsed laser-induced TOF-MS and intracavity stimulated emission. The doubly excited states are formed at the surface of the catalyst by thermal excitation through selective excitation and energy-pooling processes and are here observed outside the surface in the extended boundary layer. Experiments with ionization energy transfer indicate that no energy matching is required in reactions driven by the excitation energy.

Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection

The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function-bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces.