Dmitri Fix

Self-Healing Anticorrosion Coatings Based on pH-Sensitive Polyelectrolyte/Inhibitor Sandwichlike Nanostructures

An anticorrosion layer of a smart polymer coating is developed. The nature and properties of the coating simultaneously provide three mechanisms of corrosion protection: passivation of the metal degradation by controlled release of an inhibitor, buffering of pH changes at the corrosive area by polyelectrolyte layers, and self-curing of the film defects due to the mobility of the polyelectrolyte constituents in the layer-by-layer assembly.

Buffering polyelectrolyte multilayers for active corrosion protection

Polyelectrolyte multilayers successively deposited on an ultrasonically pre-treated metal surface demonstrate anticorrosion self-healing behaviour by the blocking of the corrosion processes without addition of any other inhibiting species due to their pH-buffering ability.

Hybrid polyester coating incorporating functionalized mesoporous carriers for the holistic protection of steel surfaces.

Given the well-documented global corrosion challenge, [ 1 ] the development of universal coating systems for metals that provide both passive and active protection is desirable. The active part of such systems typically consists of either polymer precursors [ 2 , 3 ] or effi cient corrosion inhibitors contained inside small capsules disseminated throughout the coating. [ 4–9 ] In both cases, coating rupture and the onset of corrosion trigger a release of the active molecules, which can either physically repair the passive coating [ 2 , 3 ] or form a thin impermeable fi lm over the exposed metal surface. [ 4–9 ] Previous work in our group has focused on the use of corrosion inhibitors; the technology is well-established for aluminium surfaces and typically employs a hybrid sol-gel fi lm as the coating matrix. [ 8–10 ] However, despite some effort, no similarly effective system has been found for steel. [ 4 , 11 ] When applied to steel the same sol-gel fi lm tends to form a noticeably permeable coating that is highly susceptible to corrosive attack. [ 4 ] To improve the passive and active protection of steel, the coating matrix should be nonporous with excellent adhesion and incorporate well-dispersed capsules containing a suitable inhibitor in suffi cient quantity. Dense polymer-based coatings are a good option for the passive layer; those incorporating inhibitor directly [ 12 , 13 ] or inside capsules [ 5–7 ]

Influence of magnetic fields on magneto-aerotaxis

The response of cells to changes in their physico-chemical micro-environment is essential to their survival. For example, bacterial magnetotaxis uses the Earths magnetic field together with chemical sensing to help microorganisms move towards favoured habitats. The studies of such complex responses are lacking a method that permits the simultaneous mapping of the chemical environment and the response of the organisms, and the ability to generate a controlled physiological magnetic field. We have thus developed a multi-modal microscopy platform that fulfils these requirements. Using simultaneous fluorescence and high-speed imaging in conjunction with diffusion and aerotactic models, we characterized the magneto- aerotaxis of Magnetospirillum gryphiswaldense. We assessed the influence of the magnetic field (orientation; strength) on the formation and the dynamic of a micro-aerotactic band (size, dynamic, position). As previously described by models of magnetotaxis, the application of a magnetic field pointing towards the anoxic zone of an oxygen gradient results in an enhanced aerotaxis even down to Earths magnetic field strength. We found that neither a ten-fold increase of the field strength nor a tilt of 45° resulted in a significant change of the aerotactic efficiency. However, when the field strength is zeroed or when the field angle is tilted to 90°, the magneto-aerotaxis efficiency is drastically reduced. The classical model of magneto-aerotaxis assumes a response proportional to the cosine of the angle difference between the directions of the oxygen gradient and that of the magnetic field. Our experimental evidence however shows that this behaviour is more complex than assumed in this model, thus opening up new avenues for research.

Quantitative analysis of scanning electric current density and pH-value observations in corrosion studies

The corrosion behaviour of a well-investigated aluminium alloy AA2024-T3 in sodium chloride solution was observed via scanning vibrating and ion-selective electrode techniques. A completely new approach to the analysis of the obtained data is demonstrated. The 3D fitting procedures of current density distribution and of the local pH-values above the corroding surface allow precise quantification and localization of reactive centres. Global physical parameters such as the total anodic current and the proton production rate become accessible. Both increase simultaneously with immersion time, while their ratio remains constant.

Anisotropy in Bone Demineralization Revealed by Polarized Far-IR Spectroscopy

Bone material is composed of an organic matrix of collagen fibers and apatite nanoparticles. Previously, vibrational spectroscopy techniques such as infrared (IR) and Raman spectroscopy have proved to be particularly useful for characterizing the two constituent organic and inorganic phases of bone. In this work, we tested the potential use of high intensity synchrotron-based far-IR radiation (50–500 cm−1) to gain new insights into structure and chemical composition of bovine fibrolamellar bone. The results from our study can be summarized in the following four points: (I) compared to far-IR spectra obtained from synthetic hydroxyapatite powder, those from fibrolamellar bone showed similar peak positions, but very different peak widths; (II) during stepwise demineralization of the bone samples, there was no significant change neither to far-IR peak width nor position, demonstrating that mineral dissolution occurred in a uniform manner; (III) application of external loading on fully demineralized bone had no significant effect on the obtained spectra, while dehydration of samples resulted in clear differences. (IV) using linear dichroism, we showed that the anisotropic structure of fibrolamellar bone is also reflected in anisotropic far-IR absorbance properties of both the organic and inorganic phases. Far-IR spectroscopy thus provides a novel way to functionally characterize bone structure and chemistry, and with further technological improvements, has the potential to become a useful clinical diagnostic tool to better assess quality of collagen-based tissues.

The role of angular reflection in assessing elastic properties of bone by scanning acoustic microscopy

For an assessment of the mechanical performance of bone, a quantitative description of its mechanical heterogeneity is necessary. Previously, scanning acoustic microscopy (SAM) was used as a non-destructive method to estimate bone stiffness on the micrometer scale. While up to now only the normal incidence of acoustic waves is taken into account, we extend in our study the evaluation procedure by considering the full opening of the acoustic lens. The importance of this technical aspect is demonstrated by determining the contrast in Youngs modulus between newly formed osteons and the surrounding higher mineralized interstitial bone. Several regions of human cortical bone of a femur in cross-section were imaged. For all the regions quantitative backscattered-electron imaging (qBEI) to estimate the local mass density was combined with SAM measurements. These measurements reveal a non-monotonic dependence between acoustic reflectivity and Youngs modulus, which shows that it is actually necessary to consider the lens opening in a quantitative way. This problem was experimentally and theoretically approached by using lenses with two different opening angles operated at different frequencies (52° at 400MHz and 80° at 820MHz) to image the same specimen. The mass density of bone in osteons was found to be 1930kg/m(3) on average, while the higher mineral content in interstitial bone results in a 9% increase of the density. The contrast in the effective Youngs modulus E, as determined through SAM, is more pronounced, with an average value of 14GPa in osteons and a more than 60% increase in interstitial bone. Additionally, SAM maps show oscillations in E with a periodicity of the typical bone lamella thickness of approximately 7µm in both osteons and interstitial bone. This mechanical heterogeneity can be explained by the varying orientation of the mineralized collagen fibers.