Nanocomposite coatings are of great interest as barrier coatings since synergy effects between matrix and additive properties can be achieved. This, however, requires favorable additive-matrix interactions to provide a strong interphase (interface region). In this work we elucidate the properties of two environmentally benign nanocomposite coatings based on a waterborne acrylate formulation with additives from renewable sources, i.e. either cellulose nanocrystals, CNC; or, alternatively, cellulose nanofibrils, CNF. We focus on the corrosion protective properties of these coatings and discuss the reason why the nanocomposite with CNC displays favorable corrosion protection properties whereas that with CNF does not. To this end we utilized scanning electron microscopy, water contact angle measurement, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy techniques to investigate the microstructure, surface wetting, interactions between cellulosic materials and matrix as well as corrosion protective properties of both composite coatings.

Chemical interactions between aqueous vanadium species and aluminium alloy AA6063-T5 were investigated in vanadate-containing NaCl solutions. Confocal Raman and X-ray photoelectron spectroscopy experiments were utilised to gain insight into the mechanism of corrosion inhibition by vanadates. A greenish-grey coloured surface layer, consisting of V+4 and V+5 polymerized species, was seen to form on the alloy surface, especially on top of cathodic micrometre-sized IMPs, whereby suppressing oxygen reduction kinetics. The results suggest a two-step mechanism of corrosion inhibition in which V+5 species are first reduced to V+4 or V+3 species above cathodic IMPs, and then oxidized to mixed-valence V+5/V+4 polymerized compounds.

The present investigation highlights corrosion protection of carbon steel by a waterborne acrylate-based matrix coating, with and without reinforcement by cellulose nanocrystals, by using electrochemical impedance spectroscopy in 0.1 M NaCl solution over a period of 35 days. Interactions between cellulose nanocrystals and the matrix coating were demonstrated by Fourier transform infrared spectroscopy. The results show that both coatings have high barrier performance but different protective characteristics during long-term exposure. The differences can be attributed to the reinforcement effect of cellulose nanocrystals caused by hydrogen bonding interactions between cellulose nanocrystals and the matrix coating.

The formation of a bridging gas meniscus via cavitation or nanobubbles is considered the most likely origin of the submicrometer long-range attractive forces measured between hydrophobic surfaces in aqueous solution. However, the dynamics of the formation and evolution of the gas meniscus is still under debate, in particular, in the presence of a thin air layer on a superhydrophobic surface. On superhydrophobic surfaces the range can even exceed 10 mu m. Here, we report microscopic images of the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. This is achieved by combining laser scanning confocal microscopy and colloidal probe atomic force microscopy. The configuration allows determination of the volume and shape of the meniscus, together with direct calculation of the Young-Laplace capillary pressure. The long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.

Nature lubricates in aqueous environment, and thus the example of a human synovial joint with its seamless function has been a fascination for scientists since the times of the birth of modern science. Here, inspired by nature, we investigate the mechanistic function of three different types of synergistic molecular aggregates. Firstly, we show how simple phospholipids lubricate hydrophilic model surfaces of silica and how this lubrication is facilitated further by the presence of an anionic polysaccharide, hyaluronan, due to the enhanced surface build-up of lubricant material. Next, we mimic natural polylectrolytesurfactant aggregation by employing a highly positively charged polyelectrolyte and anionic surfactant that strongly associate both in the bulk and at the surfaces by building structured aggregates that lubricate due to hydration lubrication. This occurs despite of the presence of strong attraction between the lubricated surfaces. This is an example of synergistic lubrication due to particular internal structural arrangement of the aggregates. Finally, we investigate the case of synergistic lubrication due to preferential surface ordering of two biological polyelectrolytes, cartilage oligomeric matrix protein and lubricin, that leads to favourable lubrication.

Understanding the complex and dynamic nature of calcite surfaces under ambient conditions is important for optimizing industrial applications. It is essential to identify processes, their reversibility, and the relevant properties of CaCO3 solid-liquid and solid-gas interfaces under different environmental conditions, such as at increased relative humidity (RH). This work elucidates changes in surface properties on freshly cleaved calcite (topography, wettability and surface forces) as a function of time (<= 28 h) at controlled humidity (<= 3-95 %RH) and temperature (25.5 degrees C), evaluated with atomic force microscopy (AFM) and contact angle techniques. In the presence of humidity, the wettability decreased, liquid water capillary forces dominated over van der Waals forces, and surface domains, such as hillocks, height about 7.0 angstrom, and trenches, depth about -3.5 angstrom, appeared and grew primarily in lateral dimensions. Hillocks demonstrated lower adhesion and higher deformation in AFM experiments. We propose that the growing surface domains were formed by ion dissolution and diffusion followed by formation of hydrated salt of CaCO3. Upon drying, the height of the hillocks decreased by about 50% suggesting their alteration into dehydrated or less hydrated CaCO3. However, the process was not entirely reversible and crystallization of new domains continued at a reduced rate.

The molecular mechanisms responsible for outstanding lubrication of natural systems, like articular joints, have been the focus of scientific research for several decades. One essential aspect is the lubrication under pressure, where it is important to understand how the lubricating entities adapt under dynamic working conditions in order to fulfill their function. We made a structural investigation of a model system consisting of two of the molecules present at the cartilage interface, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and hyaluronan, at high hydrostatic pressure. Phospholipid layers are found at the cartilage surfaces and are able to considerably reduce friction. Their behavior under load and varied solution conditions is important as pressures of 180 bar are encountered during daily life activities. We focus on how divalent ions, like Ca2+, affect the interaction between DPPC and hyaluronan, as other investigations have indicated that calcium ions influence their interaction. It could be shown that already low amounts of Ca2+ strongly influence the interaction of hyaluronan with DPPC. Our results suggest that the calcium ions increase the amount of adsorbed hyaluronan indicating an increased electrostatic interaction. Most importantly, we observe a modification of the DPPC phase diagram as hyaluronan absorbs to the bilayer which results in an L-alpha-like structure at low temperatures and a decoupling of the leaflets forming an asymmetric bilayer structure.

The mechanical properties of hydrogels are of importance in many applications, including scaffolds and drug delivery vehicles where the release of drugs is controlled by water transport. While the macroscopic mechanical properties of hydrogels have been reported frequently, there are less studies devoted to the equally important nanomechanical response to local load and shear. Scanning probe methods offer the possibility to gain insight on surface nanomechanical properties with high spatial resolution, and thereby provide fundamental insights on local material property variations. In this work, we investigate the local response to load and shear of poly(2-hydroxyethyl methacrylate) hydrogels with two different cross-linking densities submerged in aqueous solution. The response of the hydrogels to purely normal loads, as well as the combined action of load and shear, was found to be complex due to viscoelastic effects. Our results show that the surface stiffness of the hydrogel samples increased with increasing load, while the tip-hydrogel adhesion was strongly affected by the load only when the cross-linking density was low. The combined action of load and shear results in the formation of a temporary sub-micrometer hill in front of the laterally moving tip. As the tip pushes against such hills, a pronounced stick-slip effect is observed for the hydrogel with low cross-linking density. No plastic deformation or permanent wear scar was found under our experimental conditions.

Propofol is an amphiphilic small molecule that strongly influences the function of cell membranes, yet data regarding interfacial properties of propofol remain scarce. Here we consider propofol adsorption at the air/water interface as elucidated by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS data show that propofol adsorbed at the air/ water interface interacts with water strongly in terms of hydrogen bonding and weakly in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied there is almost no change in the orientation adopted at the interface. Data from NR show that propofol forms a dense monolayer with a thickness of 8.4 angstrom and a limiting area per molecule of 40 angstrom(2), close to the value extracted from surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded as long as the solubility limit is not exceeded. Additionally, measurements of the 1H NMR chemical shifts demonstrate that propofol does not form dimers or multimers in bulk water up to the solubility limit.