Oxygen plasma functionalization of poly(p-phenilene sulphide)

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100 W. The electron density and temperature were measured with a double Langmuir probe and were 4 × 10¹⁵ m⁻³ and 3 eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4 × 10²¹ m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7 × 10⁻³ N/m or/and increased to 7 × 10⁻² N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20 at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.     

Effect of field direction on electrowetting in a nanopore

We manifest a significant influence of field direction and polarity on surface wetting, when the latter is tuned by application of an external electric field. Thermodynamics of field-induced filling of hydrocarbon-like nanopores with water is studied by open ensemble molecular simulation. Increased field strength consistently results in water-filling and electrostriction in hydrophobic nanopores. A threshold field commensurate with surface charge density of about one elementary charge per 10 nm2 suffices to render prototypical paraffin surfaces hydrophilic. When a field is applied in the direction perpendicular to the confining walls, the competition between orientational polarization and angle preferences of interfacial water molecules relative to the walls results in an asymmetric wettability of opposing surfaces (Janus interface). Reduction of surface free energy observed upon alignment of confinement walls with field direction suggests a novel mechanism whereby the applied electric field can operate selectively on water-filled nanotubes while empty ones remain unaffected.     

Wettability and surface composition of partly and fully regenerated cellulose thin films from trimethylsilyl cellulose

The wettability and surface free energy (SFE) of partly and fully regenerated cellulose model surfaces from spin coated trimethylsilyl cellulose were determined by static contact angle (SCA) measurements. In order to gain detailed insight into the desilylation reaction of the surfaces the results from SCA measurements were compared with data from other surface analytical methods, namely thickness measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Additionally, the influence of ultra high vacuum treatment (UHV) during XPS measurements on the water wettability and surface morphology of regenerated cellulose thin films was investigated. The wetting of polar and non-polar liquids increased with prolonged regeneration time, which is reflected in the higher SFE values and polarities of the films. After UHV treatment the water SCA of partly regenerated films decreases, whereas fully regenerated cellulose shows a higher water SCA. Therefore it is assumed that volatile desilylation products tend to adsorb on partly regenerated films, which strongly influences their wettability.     

Elaboration of nano-structured grafted polymeric surface

The surface grafting of multi-polymeric materials can be achieved by grafting as components such as polymers poly(N-isopropylacrylamide) and/or surfactant molecules (hexatrimethylammonium bromide, polyoxyethylene sorbitan monolaurate). The chosen grafting techniques, i.e. plasma activation followed by coating, allow a large spectrum of functional groups that can be inserted on the surface controlling the surface properties like adhesion, wettability and biocompatibility. The grafted polypropylene surfaces were characterized by contact angle analyses, XPS and AFM analyses. The influence of He plasma activation, of the coating parameters such as concentrations of the various reactive agents are discussed in terms of hydrophilic character, chemical composition and morphologic surface heterogeneity. The plasma pre-activation was shown inevitable for a permanent polymeric grafting. PNIPAM was grafted alone or with a mixture of the surfactant molecules. Depending on the individual proportion of each component, the grafted surfaces are shown homogeneous or composed of small domains of one component leading to a nano-structuration of the grafted surface.     

Effects of airborne fluoride on soil and vegetation

The study was initiated by the sudden uncontrolled release of airborne fluorides in 2005 into the environment from aluminium smelter factory that caused damage of vegetation. Samples of corn leaves and corn male flower heads with visible symptoms of fluoride intoxication had been collected in autumn 2005. Increased contents of total fluoride, which exceeded the maximum allowable content of fluorine in feeding stuffs, including meadow grass, were detected. During continuation of the study some commercially available herbal teas and plants used for preparing herbal teas infusions, collected in the field in 2010, were investigated to investigate possible uptake of fluoride from the soil. Nettle (Urtica dioica) has been found to be a promising passive bioindicator for monitoring phytotoxic effects of fluoride in the soil on the vegetation. Good correlation between labile free fluoride in the soil and total fluoride in the nettle has been found, while total fluoride in the soil, soil pH and the dominant wind direction were also proven as important factors influencing the uptake of fluoride by the nettle.     

Low-Temperature Toluene Oxidation on Fe-Containing Modified SBA-15 Materials

Transition metals as catalysts for total VOC oxidation at low temperatures (150–280 °C) are a big challenge nowadays. Therefore, iron-modified SBA-15, AlSBA-15, and ZrSBA-15 materials with 0.5 to 5.0 wt.% Fe loading were prepared and tested for toluene oxidation. It was found that increasing Fe loading significantly improved the rate of oxidation and lowered the temperature of achieving 100% removal of toluene from above 500 °C for the supports (AlSBA-15 and ZrSBA-15) to below 400 °C for 5FeZrSBA-15. The formation of finely dispersed iron oxide active sites with a particle size less than 5 nm was observed on all the SBA-15, AlSBA-15, and ZrSBA-15 supports. It was found that the surface properties of the mesoporous support due to the addition of Al or Zr predetermined the type of formed iron oxide species and their localization on the support surface. Fe-containing SBA-15 and AlSBA-15 showed activity in total toluene oxidation at higher temperatures (280–450 °C). However, 5 wt. % Fe-containing ZrSBA-15 showed excellent activity in the total oxidation of toluene as a model VOC at lower temperatures (150–380 °C) due to the synergistic effect of Fe-Zr and the presence of accessible and stable Fe²⁺/Fe³⁺ active sites.