A novel bilayer coating system for autonomous corrosion-triggered self-healing is demonstrated. The storage of the encapsulated monomer and the catalyst is separated in two different layers. The encapsulated catalyst is stored inside a metallic coating, which ensures its activity even for an extended exposure time. The release from the capsules is triggered by corrosion and the correlated pH increase.
Raman spectroscopy in a confocal microscope was used to study electrochemically synthesized corrosion products from sour gas experiments. When exposed to oxygen-containing atmosphere, the initial mackinawite FeS corrosion product transformed under laser irradiation to hematite, Fe 2 O 3 . Measurements with a thin water layer on top of the corrosion products prevented the transformation, as drying was prevented. In situ Raman measurements of mackinawite formation avoided the problem of transformation completely. In situ and operando, the initially formed mackinawite showed two Raman peaks in the wavenumber range >180 cm −1 centered around 200-215 cm −1 and 285-300 cm −1 . On an empirical basis, these modes were assigned to a B 1g mode of the iron sublattice and an A 1g mode of the sulfur sublattice, respectively. A comparison with a literature assignment for aged mackinawite suggests that the aging observed involves significant changes in the sulfur sublattice. Corrosion of iron in H 2 S containing solutions is a general problem in crude oil and natural gas production, and is generally referred to as sour corrosion. Aqueous H 2 S solutions promote corrosion of steels, [1][2][3] but the exact nature and mechanisms of corrosion strongly depend on the reaction conditions. 4-7 While the process has been widely investigated for pure iron, [8][9][10][11][12] and carbon steels, [13][14][15][16][17] there is still a lack of understanding of the reaction path and electronic properties of the corrosion products. 18,19The chemistry of the corrosion products formed during H 2 Striggered corrosion is rather complex, as there are many different solids consisting only of iron and sulfur. 20 However, mackinawite has been found to be the initial, 8,21 and probably most important corrosion product, of iron in aqueous sulfide solutions as it was observed in reactions carried out over a wide range of pH and temperature. 11,19,[22][23][24] It possesses a tetragonal, layered crystal structure, [25][26][27] and can be synthesized by precipitation from solutions containing Fe 2+ and S 2− solutions, 28,29 or by reaction of sulfide solution with metallic iron. 19,21,26,30 In the field of microbially induced corrosion, sulfatereducing bacteria are known to transform sulfate compounds into iron sulfides, e.g. mackinawite. [31][32][33][34][35][36] Raman spectroscopy has become an important tool for identification of corrosion products. [37][38][39][40][41][42][43][44][45] Some major problems may still occur due to laser heating, fluorescence, or low sensitivity as a consequence of the small cross-sections of Raman scattering. However, the fact that glass and water are both very weak Raman scatterers makes this technique suitable for in situ measurements in aqueous environments. 46-48The presence of water has an additional positive effect on the process as it decreases the heating from the laser. The use of (in situ and operando) Raman spectroscopy for study corrosion process studies of iron in sulfide rich environments has been already repor...
Protein structure is highly diverse when considering a wide range of protein types, helping to give rise to the multitude of functions that proteins perform. In particular, certain proteins are known to adopt a knotted or slipknotted fold. How such proteins undergo mechanical unfolding was investigated utilizing a combination of single molecule atomic force microscopy (AFM), protein engineering and steered molecular dynamics (SMD) simulations to show the mechanical unfolding mechanism of the slipknotted protein AFV3-109. Our results reveal that the mechancial unfolding of AFV3-109 can proceed via multiple parallel unfolding pathways that all cause the protein slipknot to untie, and the polypeptide chain to completely extend. These distinct unfolding pathways proceed either via a two-state or three-state unfolding process involving the formation of a well-defined, stable intermediate state. SMD simulations predict the same contour length increments for different unfolding pathways as single molecule AFM results, thus provding a plausible molecular mechanism for the mechanical unfolding of AFV3-109. These SMD simulations also reveal that two-state unfolding is initiated from both the N- and C-termini, while three-state unfolding is initiated only from the C-terminus. In both pathways, the protein slipknot was untied during unfolding, and no tightened slipknot conformation observed. Detailed analysis revealed that interactions between key structural elements lock the knotting loop in place, preventing it from shrinking and the formation of a tightened slipknot conformation. Our results demonstrate the bifurcation of the mechancial unfolding pathway of AFV3-109, and point to the generality of a kinetic partitioning mechanism for protein folding/unfolding.
We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single-molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water (H(2)O) with deuterium oxide (D(2)O). Using a combination of force protocols, we demonstrate that protein unfolding, protein collapse, protein folding and a chemical reaction are affected in different ways by substituting H(2)O with D(2)O. We find that D(2)O molecules form an integral part of the unfolding transition structure of the immunoglobulin module of human cardiac titin, I27. Strikingly, we find that D(2)O is a worse solvent than H(2)O for the protein I27, in direct contrast with the behaviour of simple hydrocarbons. We measure the effect of substituting H(2)O with D(2)O on the force dependent rate of reduction of a disulphide bond engineered within a single protein. Altogether, these experiments provide new information on the nature of the underlying interactions in protein folding and chemical reactions and demonstrate the power of single-molecule techniques to identify the changes induced by a small change in hydrogen bond strength.
Polymer coatings are widely used to protect metals from corrosion. Coating adhesion to the base material is critical for good protection, but coatings may fail because of cathodic delamination. Most of the experimental studies on cathodic delamination use polymers to study the corrosion behavior under conditions where the interfacial chemistry at the metal(oxide)/polymer interface is not well-defined. Here, ultrathin linear and cross-linked poly(methyl methacrylate) [PMMA] coatings that are covalently bound to oxide-covered zinc via a silane linker have been prepared. For preparation, zinc was functionalized with vinyltrimethoxysilane (VTS), yielding a vinyl monomer-covered surface. These samples were subjected to thermally initiated free radical polymerization in the presence of methyl methacrylate (MMA) to yield surface-bound ultrathin PMMA films of 10-20 nm thickness, bound to the surface via Zn-O-Si bonds. A similar preparation was also carried out in the presence of different amounts of the cross-linkers ethylene glycol diacrylate and hexanediol diacrylate. Functionalized and polymer-coated zinc samples were characterized by infrared (IR) spectroscopy, secondary ion mass spectrometry (SIMS), ellipsometry, and X-ray photoelectron spectroscopy (XPS). Coating stability toward cathodic delamination has been evaluated by scanning Kelvin probe (SKP) experiments. In all cases, the covalently linked coatings show lower delamination rates of 0.02-0.2 mm h(-1) than coatings attached to the surface without covalent bonds (rates ∼10 mm h(-1)). Samples with a higher fraction of cross-linker delaminate slower, with rates down to 0.03-0.04 mm h(-1), compared to ∼0.3 mm h(-1) without cross-linker. Samples with longer hydrophobic alkyl chains also delaminate slower, with the lowest observed delamination rate of 0.028 mm h(-1) using hexanediol diacrylate. For the coatings studied here, delamination kinetics is not diffusion limited, but the rate is controlled by a chemical reaction. Several possibilities for the nature of this reaction are discussed; radical side reactions of the oxygen reduction are the most likely path of deadhesion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.