Mikael Järn

Microbe repelling coated stainless steel analysed by field emission scanning electron microscopy and physicochemical methods

Coating of stainless steel with diamond-like carbon or certain fluoropolymers reduced or almost eliminated adhesion and biofilm growth of Staphylococcus epidermidis, Deinococcus geothermalis, Meiothermus silvanus and Pseudoxanthomonas taiwanensis. These species are known to be pertinent biofilm formers on medical implants or in the wet-end of paper machines. Field emission scanning electron microscopic analysis showed that Staph. epidermidis, D. geothermalis and M. silvanus grew on stainless steel using thread-like organelles for adhesion and biofilm formation. The adhesion threads were fewer in number on fluoropolymer-coated steel than on plain steel and absent when the same strains were grown in liquid culture. Psx. taiwanensis adhered to the same surfaces by a mechanism involving cell ghosts on which the biofilm of live cells grew. Hydrophilic (diamond-like carbon) or hydrophobic (fluoropolymer) coatings reduced the adherence of the four test bacteria on different steels. Selected topographic parameters, including root-mean-square roughness (Sq), skewness (Ssk) and surface kurtosis (Sku), were analysed by atomic force microscopy. The surfaces that best repelled microbial adhesion of the tested bacteria had higher skewness values than those only slightly repelling. Water contact angle, measured (θm) or roughness corrected (θy), affected the tendency for biofilm growth in a different manner for the four test bacteria.

H2S modified atomic layer deposition process for photocatalytic TiO2 thin films

H2S modified TiO2 films were grown by atomic layer deposition (ALD) using TiCl4, H2S and water as precursors. The films were characterized by XRD, XPS, TOF-SIMS, SEM and UV-VIS spectrometry. Photocatalytic activities of the films under UV and visible light were determined by the degradation of a thin layer of stearic acid. Light induced superhydrophilicity of the films was also studied. Although the sulfur content of the films was very low, substantial modification of the film properties occurred. All the films prepared at 400 and 500 °C with H2S were photocatalytically active under visible light. Photocatalytic activity under UV irradiation of the H2S modified films was also drastically improved when proper deposition parameters were applied.

Wetting studies of hydrophilic-hydrophobic TiO2@SiO2 nanopatterns prepared by photocatalytic decomposition.

TiO(2)@SiO(2) nanopatterns were prepared with the evaporation-induced self-assembly (EISA) technique. The material consists of an ultrathin (approximately 2 nm) layer of titania with hexagonally ordered craters of roughly 30 nm in diameter, on a silica substrate. The open pore structure and high homogeneity of the pattern makes these materials ideal for detailed wetting studies. The nanopatterns were functionalized with a fluoroalkylsilane (FAS), which attached on both titania and silica, resulting in a hydrophobic surface. By irradiating the composite material with UV light for different lengths of time, the hydrophilic/hydrophobic contrast in the nanopattern could be tuned. This is a result of the very different photocatalytic properties of titania and silica. The area fraction covered with FAS, f(FAS), as a function of UV irradiation time was calculated from water contact angle measurements of the composite film and corresponding reference samples, by using existing wetting models for heterogeneous surfaces. The results were compared to area fractions derived from X-ray photoelectron spectroscopy (XPS). f(FAS)-values determined from static water contact angles gave the best agreement with XPS, while advancing and receding contact angles overestimated and underestimated the f(FAS)-values, respectively. The Cassie model gave a slightly better fit to the XPS data than the Israelachivili model.

Optimizing the performance of tin dioxide microspheres for phosphopeptide enrichment

Phosphopeptide enrichment based on metal oxide affinity chromatography is one of the most powerful tools for studying protein phosphorylation on a large scale. To complement existing metal oxide sorbents, we have recently introduced tin dioxide as a promising alternative. The preparation of SnO(2) microspheres by the nanocasting technique, using silica of different morphology as a template, offers a strategy to prepare materials that vary in their particle size and their porosity. Here, we demonstrate how such stannia materials can be successfully generated and their properties fine-tuned in order to obtain an optimized phosphopeptide enrichment material. We combined data from liquid chromatography-mass spectrometry experiments and physicochemical characterization, including nitrogen physisorption and energy-dispersive X-ray spectroscopy (EDX), to explain the influence of the various experimental parameters.

Bioinspired Synthesis of Superhydrophobic Coatings

A superhydrophobic material prepared by precipitating calcium phosphate on TiO2 films under in vitro conditions is described. Crystalline calcium phosphate is very porous with octacalcium phosphate as the main phase. The films are made hydrophobic by the surface grafting of a perfluorophosphate surfactant (Zonyl FSE). The as-prepared coatings were strongly hydrophobic, with advancing contact angles exceeding 165 degrees and receding angles exceeding 150 degrees . The formation of the calcium phosphate layer is self-organizing, and the coating is easily functionalized. The material was characterized with dynamic contact angle measurements, SEM, XRD, and XPS. The strong water repellency is explained by the open porous morphology of the calcium phosphate coating together with the successful attachment of the hydrophobic function.

Influence of surface structure on wetting of coated offset papers

Abstract To obtain more knowledge of the properties affecting print quality and adhesion characteristics in the printing process, attention has been directed to the nature of surface energy. The aim was to compare different surface-energy calculation models and to investigate the influence of surface roughness on wetting of coated offset papers. The wetting process was studied by static contact angle measurements using a series of reference liquids. Topographical characterization was carried out using atomic force microscopy. Surface energy components were determined using different calculation models. The determination can be considerably simplified using a mono-monopolar model, which has been proven in previous studies. The surface energy components were derived from both apparent and topography-corrected contact angles. The surface topography had a significant effect on wetting of the samples studied.

Iron Oxide Doped Alumina-Zirconia Nanoparticle Synthesis by Liquid Flame Spray from Metal Organic Precursors

The liquid flame spray (LFS) method was used to make iron oxide doped alumina-zirconia nanoparticles. Nanoparticles were generated using a turbulent, high-temperature (𝑇max∼3000 K) H2-O2 flame. The precursors were aluminium-isopropoxide, zirconium-𝑛-propoxide, and ferrocene in xylene solution. The solution was atomized into micron-sized droplets by high velocity H2 flow and introduced into the flame where nanoparticles were formed. The particle morphology, size, phase, and chemical composition were determined by TEM, XRD, XPS, and N2-adsorption measurements. The collected particulate material consists of micron-sized aggregates with nanosized primary particles. In both doped and undoped samples, tetragonal phase of zirconia was detected in room temperature while alumina was found to be noncrystalline. In the doped powder, Fe was oxidized to Fe2O3. The primary particle size of collected sample was approximately from 6 nm to 40 nm. Doping was observed to increase the specific surface area of the powder from 39 m2/g to 47 m2/g.

Influence of long-term aqueous exposure on surface properties of plasma-sprayed oxides Cr2O3 and Cr2O3–25 wt% TiO2

The influence of water exposure on the surface properties of plasma-sprayed Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) was studied. It was shown that both plasma-sprayed materials contained Cr(VI) hydrous oxide phases, which dissolved rapidly at the beginning of water exposure. The dissolution continued slowly during the whole water exposure time. The Cr(VI) dissolution was accompanied by a rapid increase in surface IEP value. Both Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) showed similar dissolution, zeta potential, and surface oxidation states. Thus the addition of TiO(2) did not influence the surface properties of the plasma-sprayed Cr(2)O(3).

Radial Spreading of Inks and Model Liquids on Heterogeneous Polar Surfaces

Novel models are developed and previously published simple models characterizing the spreading of probe liquids and inks on solid surfaces are evaluated with water and ethylene glycol. The aim is to determine the most appropriate models which would be suitable to describe liquid and ink spreading on both chemically and structurally heterogeneous paper surfaces. The surface energy and its components (Lifshitz–van der Waals, acid and base) for the paper samples have previously been characterized at semi-equilibrium conditions. The equilibrium work of adhesion and work of spreading is found to be linearly related to the maximum print tack force of model inks. The dynamic spreading are found to be determined by coupled spreading mechanisms, being related both to the surface structure and surface chemistry.

Dynamic Spreading of Polar Liquids on Offset Papers

The aim of this study was to investigate the spreading of sessile drops of polar probe liquids (water and ethylene glycol) on pigment coated offset papers. Furthermore, existing theoretical models for spreading were applied to evaluate the experimental results. The hydrodynamic model gave a better fit to the results at lower spreading rates, while the molecular-kinetic theory gave a good fit over a larger velocity range. Factors introduced to correct for the exponential dependency on time of the drop base radius and its contact angle can be interpreted as coupled processes. Differences in the spreading between the papers were found to correlate with the acid and base components of the surface energy, rather than with differences in surface roughness.