We investigated the physicochemical surface properties of different highly aligned nitrogen-doped multi-walled carbon nanotube (N-MWCNT) carpets, synthesized using toluene/pyrazine, toluene/benzylamine and acetonitrile via a sublimation-based chemical vapor deposition (SCVD) method at 760 degrees C. The surfaces of the N-MWCNT carpets synthesized using toluene/pyrazine and toluene/benzylamine were very hydrophobic. In contrast, we observed a complete wetting of the N-MWCNT carpets synthesized using acetonitrile. The difference in the wetting behavior of these N-MWCNT carpets is the main focus in this study and was not investigated before. Here, we show that not only the presence or concentration of nitrogen inside the carbon lattice, but especially it's kind of incorporation have an important influence on the surface polarity. (C) 2018 Elsevier Ltd. All rights reserved.

Omniphobic and superomniphobic sol-gel coatings have been prepared on technical scale by sol-gel formulations modified with a perfluoropolyether and/or a fluoropolymer nanoparticle dispersion. Single and two-layer coatings were prepared by spraying or coating with a doctor blade. They exhibited a broad range of different morphologies leading to different wetting behavior. Under certain preparation conditions (spraying at elevated temperature, high surface coverage), the single-layer coatings with perfluoropolyether and fluoropolymer nanoparticles exhibited a hierarchical structuring at various length scales, high roughness and aspect ratio, re-entrant structures and superomniphobic behavior. The mechanical stability of these layers was sufficient to maintain superhydrophobicity and oleophobicity after a harsh wet abrasion test. Two-layer coatings with a smooth low-energy top coat on a rough fluorine-free base coat had a higher mechanical stability but showed an insatisfactory wetting behavior. Systematic investigation of the correlations between roughness, liquid surface tension and advancing/receding contact angle of water, water-ethanol mixtures and hexadecane confirmed the existing theories. The self-cleaning properties of the rough coatings were good for polar soils; for oils they are very sensitive to layer defects.

Multiwalled carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition and subsequently purified by applying a high temperature annealing process. The annealed material was characterized using Raman spectroscopy. Next, the interaction of the annealed MWCNTs with polycarboxylate (PCE) comb-copolymer surfactants was studied regarding the quality of dispersion in water, with a focus on the influence of the critical parameters temperature and pH. Optical micrographs and integral light transmission measurements revealed that both temperature and pH strongly impact the dispersion quality of the MWCNTs. Dynamic light scattering and zeta potential measurements of aqueous solutions of the diluted PCE samples proved that conformational changes occur in dependence on temperature as well as pH. Moreover, it was found that specific molecular conformations strongly affect their efficiency to disperse MWCNTs. On the basis of these experimental findings, a scheme illustrating the consequences of PCE coiling and stretching on successful CNT dispersion in water is presented.

The immobilisation of silica nanoparticles on the surface of a flowing polymer melt is studied during injection moulding. We use silica nanoparticles of identical size of about 200 nm, but with different surface functionalities: plain unmodified particles with silanole groups as well as amino-and hydrocarbon modified particles. The particles were brought in contact with a polycarbonate melt at a temperature of 300 degrees C. In our investigation, we show that particles with polar surfaces are more embedded than those with non-polar surfaces. Immobilised polar particles exhibited also a higher adhesion, tested with an adhesive tape, whereas the non-polar particles can be easily removed by peeling off the adhesive tape. This paper reveals that surface properties have a larger influence on embedding of nanoparticles than thermal conditions due to cooling of the melt.

Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different extruded polypropylene- and polyethylene-based wood–plastic composite (WPC) formulations. The surfaces were analysed using stereophotogrammetry, high-resolution scandisk confocal microscopy and scanning electron microscopy, resulting in detailed information about the topography and surface morphology. In addition, dynamic water contact angle measurements were carried out to characterize the wettability of the samples. The effects of polymer type, polymer content, additive content and processing method on the resulting topography and wetting were investigated. The correlation between topography and wetting resulted in a conceptual model of WPC surface morphology and wetting, which may be applied to optimize adhesion properties of this composite material.

Using the example of carbon nanoparticles of different functionality and shape, the possibilities of a comprehensive surface characterization are presented. In the focus of the analytical work lie electrokinetic and wetting measurements, which were supplemented by X-ray photoelectron spectroscopy and gas sorption measurements. Thus, the chemical functionality, the surface energy as well as the topography of the particle surfaces can be described quantitatively. Knowing these variables allows a targeted selection of particles as reinforcing materials as well as nucleating agents.

Polyethylene terephthalate multifilament fabrics used as filtration and operating room textiles possess through-thickness pore channels at the yarn intersections (meso-pores). These pore channels pose a risk for the penetration of contaminated fluids and particles. The size of pore channels may be reduced by high-density weaving. However, this leads to reduced drapability and thus to degraded application properties of the fabric. To satisfy the requirements without impeding the physiological properties of the textile, fluid- and particle-tight fabrics are developed. This was realized by partial immobilization of functionalized micro particles into the meso-pores. A reduction of the pore size without complete pore-closure is achieved by establishing a net-like particle structure in the meso-pores. To match the requirements of intensive use, permanent particle-bonding to the fiber surface is necessary. This can be achieved by suitable polyethylene terephthalate fabric surface-modification, dependent on the particle functionalization. The investigations have shown that functionalized particles establish a very good inter particle bonding as well as to the fiber surface. An increased permanent bonding can be realized by a modification of the fabric surface which is tuned to the functionalization of the particle.

Two types of carbon‐based materials, i.e., mesoporous carbon and HNO3‐oxidized carbon nanotubes, with nearly the same specific surface area and abundant in surface oxygen‐containing functional groups were selected in order to examine their effect on the hydration of tricalcium silicate (C3S), the main portland cement component, in early stages. Different methods, including XPS and TG‐MS analyses, electrokinetic potential measurements, as well as determination of adsorption capacity for calcium ions from aqueous solutions, were used to investigate the physicochemical surface properties of the selected carbon‐based materials. It was found that the carbon‐based materials with high specific surface area and rich in oxygen‐containing functional groups on their surfaces have a catalytic effect on early C3S hydration. It was observed that the modification of C3S paste with the selected materials added in high concentrations (1 wt% and higher) led to an increase in the rate and degree of C3S hydration in the early stages. The mechanism of early C3S hydration accelerated by carbon‐based materials rich in surface functional groups was clarified by the example of the mesoporous carbon. It was found that the oxygen‐containing functional groups present on the carbon surface have both an influence on the content of calcium ions in the aqueous phase of the C3S paste and an indirect positive effect in relation to the specific surface of C3S.

Controlling the reversibility, quantity, and extent of biomolecule interaction at interfaces has a significant relevance for biomedical and biotechnological applications, because protein adsorption is always the first step when a solid surface gets in contact with a biological fluid. Polymer brushes, composed of end-tethered linear polymers with sufficient grafting density, are very promising to control and alter interactions with biological systems because of their unique structure and distinct collaborative response to environmental changes. We studied protein adsorption and cell adhesion at polymer brush substrates which consisted of poly(N-isopropylacrylamide) (PNIPAAm), having a lower critical solution temperature (LCST), to control bioadsorptive processes by changing the environmental temperature. Preparing the PNIPAAm brushes by the "grafting-to"-method two differently synthesized PNIPAAm polymers were used, at which one possessed an additional hydrophobic terminal headgroup. It is known that hydrophobic moieties can influence protein adsorption significantly. The films were comprehensively analyzed by in situ spectroscopic ellipsometry, contact angle measurements, streaming potential, and atomic force microscopy. Our study was mainly focused on the investigation of the fibrinogen (FGN) adsorption responsiveness both on homo polymer PNIPAAm brushes with and without the hydrophobic terminal functionalization, and further on binary brushes made of the polyelectrolyte poly(acrylic acid) (PAA) and one of the prior described two PNIPAAm species. The results show that the terminal hydrophobic modification of PNIPAAm has a considerable impact on wettability, LCST, and morphology of the homo and the binary brush systems, which consequently led to an alteration of FGN adsorption. By using binary PNIPAAm-PAA brushes with different composition it was possible to induce stimuli dependent FGN adsorption with a considerable amplified switching effect by introducing a hydrophobic terminal residue to PNIPAAm. Cell adhesion studies with human mesenchymal stem cells reflected the results of the FGN adsorption.

Micropowder of poly(tetrafluoroethylene) (PTFE) can be used in base oils to improve the tribological properties significantly, if oil molecules are covalently linked to primary PTFE particles in the dispersion. Enhanced properties are not only determined by the amount of PTFE micropowder added to the oil but as well by the surface charge, radical concentration, and the size and distribution of PTFE particles in the oil phase.The chemical compatibilization (=cc) between PTFE micropowder and ester oil by the use of two types of PTFE micropowder, which differ in radical concentration and the amount of functional groups is shown. The concentration of PTFE micropowder in the dispersions was varied from 5 to 20 wt%. Both the pure PTFE micropowder and the oil-PTFE-cc dispersions were characterized by ESR and FTIR spectroscopy as well as by zeta potential measurements. Rheological and tribological tests were performed on the ester oil and the oil-PTFE-cc dispersions. Qualitative differences are discussed in terms of particle interactions, dispersion stability, chemical compatibilization efficiency and the amount of functional groups.A correlation between flow properties and surface charge of the PTFE particles within the dispersions was obtained. The influence on tribological properties is discussed as well. (C) 2014 Elsevier B.V. All rights reserved.

Different approaches, including determination of the surface tension via capillary penetration measurements and characterization of the surface chemical composition by means of X-ray photoelectron spectroscopy (XPS), were applied to reveal the surface properties of various CNT types produced from acetonitrile (CH3CN), cyclohexane (C6H12) and methane (CH4). Significant differences were found in the polarity of the CNT surfaces depending on the used precursors. The surface tension of the CNTs increases by utilization of carbon sources in the following order: cyclohexane, methane, acetonitrile. Using XPS analysis a comparatively high contents of nitrogen and oxygen atoms were detected on the surface of the CH3CN-CNTs. Based on the results of the mass spectrometry, the strong hydrophobic character observed for the C6H12-CNTs is assumed to originate from polycyclic aromatic hydrocarbons deposited on the nanotubes’ surface during synthesis. The investigation of the deposition of silica on the CNTs by a sol-gel method showed that the polar surface of the CH3CN-CNTs provided the most favorable condition for the heterogeneous precipitation of silica. In contrast, no precipitation of silica was observed on the hydrophobic C6H12-CNTs.

Single polycation cross-linked multilayers, based on poly(ethyleneimine) (PEI), have been prepared using a method of 3,3',4,4'-benzophenonetetracarboxylic-dianhydride (BTCDA)-mediated electrostatics and hydrogen bonds layer-by-layer assembly. Linear PEI [PEI(L)] and branched PEI [PEI(B)] were adsorbed from salt-free aqueous solutions, either onto silica microparticles with particle diameter of 40-60 mu m (Daisogel type) and 9-11 mu m (Davisil type) or silicon wafers. The BTCDA cross-linking of the polycation adsorbed onto the solid surface results in a surface covered with carboxylic groups. The cross-linked polycation layers, which are negatively charged over a wide range of pH, can adsorb a new positively charged polyelectrolyte layer. A regular increase of the single polycation multilayers onto silica microparticles was observed by zeta potential measurements and X-ray photoelectron spectroscopy. The immobilization of two enzymes (pepsin and lysozyme) onto the functionalized silica surface, via glutaraldehyde (GA), has been tested. The amount of the attached enzyme significantly depended on the isoelectric point of the enzyme. Surface characteristics, average height, h(a), and average roughness, R-a, slightly increased after each modification step of the organic film. (C) 2013 Elsevier B.V. All rights reserved.

Electrokinetics is a convenient tool for characterizing surface properties of solids, but also for studying adsorption processes on such surfaces. One topic of our interest was the study of the sizing process of glass fibres. With the help of streaming potential measurements using the electrokinetic analyser (EKA by Anton Paar, Graz, A), we found an interesting change of surface properties of glass fibres depending on the size composition. In case of adsorption of pure -aminopropyltriethoxisilane (AMEO) onto glass fibre surface, the resulting surface has strong basic properties with an isoelectric point () of about pH(IEP)=10. In the case of modification with a mixture of AMEO and one cationic surfactant (in our case oleyltrimethylammoniumchloride/Arquad S50), the IEP changes to pH(IEP)=6.3. The shape of the function zeta-potential vs. pH corresponds to a curve of surfaces either without any functional groups or with amphoteric properties. For us, this result was astonishing. Due to the cationic functional groups of the AMEO and the surfactant, a highly polar cationic (positively charged) surface was expected. This article discusses possible reasons for the observed behaviour.

Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different mechanically modified stainless steel surfaces. The surfaces were analyzed using high-resolution confocal microscopy, resulting in detailed information about the topographic properties. In addition, static water contact angle measurements were carried out to characterize the surface heterogeneity of the samples. The effect of morphological anisotropy on water contact angle anisotropy was investigated. The correlation between topography and wetting was studied by means of a model of wetting proposed in the present work, that allows quantifying the air volume of the interface water drop-stainless steel surface.

We investigated the adaptive adhesion properties of comb-like random copolymer brushes made of poly(ethylene glycol) (PEG)-poly(dimethylsiloxane) (PDMS) grafted on flat and rough substrates. The properties of the brush layers were investigated using ARXPS, contact angle, electrokinetics, null ellipsometry, and adhesion measurements. It was found that hydrophobic PDMS segments segregate at the brush topmost layer in the dry state. However, hydrophilic PEG chains segregate at the brush topmost layer in the wet state. The adhesion properties of fabricated materials were tested using the AFM colloid probe technique and probe tack tester. It was found that the adhesive properties depend strongly on the mechanical properties (stiff/soft) and chemical functionality (hydrophobicity/hydrophilicity) of the applied adhesion tester as well as on the chemical composition, surface roughness, and thickness of the brush. In particular, hydrophobic PDMS and hydrophilic PEG adhere more strongly to hydrophobically modified and hydrophilic native colloid probes, respectively. Thick brushes are more adhesive than thin ones, and brushes grafted to flat substrates are stickier than those grafted to rough substrates when measured with a hard AFM probe. Unlike the results of adhesion measurements performed using hard AFM probes, the PDMS surface probed by soft pressure-sensitive adhesives (PSA) is almost nonadhesive. However, PEG is strongly adhesive, and the adhesion increases with the PEG fraction in the brush when probed by both hydrophilic and hydrophobic soft adhesives. The surfaces roughness also has a considerable effect on adhesion. Contrary to the adhesion measurements performed by hard AFM colloid probes, the adhesion of rough surfaces measured with a soft PAA or SIS tack tester is greater than that on the corresponding flat one.

It has been shown that fouling processes are very complex. They are largely determined by interaction forces between the solid surface and the corresponding adherent molecules. In this article, according to the DLVO theory van der Waals- and electrostatic interactions be considered and combined with the surface topography of the solid surface. It can be shown that a variety of factors determine the adsorption behavior. Using these results, requirements may be placed on a solid surface to prevent contamination as far as possible.

A novel route to synthesize organic/inorganic hybrid microparticles containing trypsin attached on the surface was developed. Poly(vinyl amine) (PVAm) with low (15,000gmol−1) and high (340,000gmol−1) molar mass was adsorbed from salt-free aqueous solution onto silica microparticles with particle diameter of 40–60μm. Then, the enzyme was covalently bound to the surface via glutaraldehyde (GA) as cross-linker. X-ray photoelectron spectroscopy (XPS), potentiometric and polyelectrolyte titrations, and electrokinetic measurements were employed to obtain information about the polyelectrolyte adsorption and multilayer formation, as well as the amount of trypsin that has been covalently bound to the PVAm-functionalized surface. The study showed that the stability of the organic layer carrying the enzyme has been strongly influenced by the molar mass of the PVAm under the streaming fluid condition. The amount of the attached enzyme did not significantly vary with the adsorbed amount of PVAm.