The successful use of ice-binding proteins (IBPs) to develop anti-icing surfaces requires a comprehensive understanding of their working mechanism when introduced in environments distinct from the protein's natural setting. This study systematically addresses this aspect by investigating how IBPs control ice accretion when grafted onto an aluminum alloy using polyethylene glycol (PEG) linkers of various lengths and on the polymer backbone of a PEG hydrogel matrix. Freezing experiments monitored through thermal imaging reveal that the degrees of freedom of the proteins significantly influence their functionality. Specifically, we demonstrate that when the degrees of freedom of anti-freeze proteins (AFPs) are restricted by their functionalization on surfaces using short linkers or when they are present in restricted volumes in polymers, they behave as ice-nucleating proteins (INPs) promoting ice accretion. In conditions where their degrees of freedom are enhanced (long linkers, water-rich environment), AFPs effectively inhibit ice nucleation and propagation. The work underlines the relevance of protein mobility as a so far unforeseen key design factor needed to fully benefit from the potential use of natural or synthetic AFPs grafted on surfaces for cryopreservation of biological samples and the design of next-generation low-icing surfaces and coatings.

The stability of inhibiting layers on AA2024-T3 intermetallic particles (IMPs) during re-immersion in saline following an initial immersion in a Ce(III)-containing electrolyte was investigated using in situ reflected light microscopy. Re-immersion behaviour varied due to differences in IMP composition, spatial distribution, and Ce(III) precipitation. IMPs were grouped into four categories based on whether their activity was high or low during both the immersion and re-immersion stages. Majority of the high activity particles during re-immersion had low activity during immersion. Longer immersion times (up to 72 h) and a brief delay in inhibitor supply (30 s) reduced re-immersion activity by increasing Ce(III) coverage. These findings suggest that corrosion protection systems promoting greater Ce(III) precipitation may enhance re-immersion stability.

Recent works have shown the potential of diatomaceous earth (DE) as an efficient and environmentally friendly storage system for active chemicals such as corrosion inhibitors in coatings. The storage of organic inhibitors is nevertheless challenging. To address this challenge, in this work, we study the effect of surface modification of DE particles on the loading and release of organic corrosion inhibitors in solution and from coatings. To this aim, three trichlorosilanes with varying alkyl chain lengths (C4, C8, C18) were used to modify the surface of sp. Aulacoseira-type diatomite (DE). 2,5-Dimercapto-1,3,4-thiadiazolate di-potassium salts (KDMTD) were selected as a model corrosion inhibitor for its high solubility and effectiveness in protecting Cu-rich aerospace alloys, such as AA2024-T3. UV-Vis spectroscopy revealed a relationship between chain length and inhibitor loading and release, with mid-length silane (C8) adsorbing 3.5 times more inhibitor with no negative effect on release kinetics. When incorporated into epoxy-amine coatings, C8 surface modification significantly improved DE particle dispersion and protection of the inhibitor from the polymer matrix, preventing unwanted side reactions. This increased the availability of active organic inhibitors for protection at damaged sites. In-situ reflected microscopy during immersion and postmortem analysis of damaged coatings demonstrated high levels of corrosion protection and the formation of stable protective layers at damaged sites. The research opens the path to more efficient use of functional DE particles in coatings.

Polyelectrolytes with ionic domains screened by bulky hydrophobic segments form processable, hydrophobic complexes called “compleximers”. Ionic liquids, which are chemically similar, further plasticize compleximers, yet the mechanisms behind their plasticization effects and distribution within the complexes remain unclear. This study examines the relaxation dynamics of plasticized compleximers across multiple length scales using rheology, fluorescence recovery after photobleaching (FRAP), and broadband dielectric spectroscopy (BDS). The incorporation of ionic liquids into compleximers reduces their glass transition temperature (T_g), accelerates diffusive processes, increases segmental motion, and leads to a small decrease in activation energy associated with these relaxation processes. However, the activation energies vary substantially between techniques, probing different physical processes: approximately 200 kJ/mol in rheology, 50 kJ/mol in FRAP, and 90 kJ/mol in BDS. These variations suggest that collective dynamics strongly influence the compleximer rheology, making the mobilization (and activation) of polymer chains distinct from the local movement of ionic segments.

Micropatterned surfaces with both hydrophilic and hydrophobic regions are relevant for a wide range of applications from fuel cells to water harvesting systems. The preferential nucleation of water on hydrophilic regions can also be used to control frost nucleation on chemically patterned surfaces. So far, this concept has been tested on brittle silicon surfaces with only a few different sizes and shapes of hydrophilic regions. In this work, the concept of controlled icing is investigated on five polymeric surfaces with different surface energies modified by micropatterning them with three types of hydrophilic polymer brushes. Frost formation and propagation on the resulting patterned surfaces with regions of varying wettability is monitored and quantified using high-resolution thermal imaging. The study proves that control over frost nucleation and propagation using regions of varying wettability can be achieved on commodity polymers. In addition to influencing the time and location of ice nucleation, the local patterning affects the freezing propagation mode and rate due to its impact on the continuity and thickness of molecular water layers (MWL). These results show that local control over the state of MWLs is key to controlling both ice nucleation and propagation of freezing events on surfaces.

Streaking corrosion (SC) of AA7075-T6, characterized by the rapid dissolution of an altered surface layer (ASL) formed through mechanical surface treatments, is investigated. Utilizing in situ high-resolution reflected light microscopy, we reveal that SC initiates preferentially on intermetallic particles (IMP) or pre-existing pits. Optical evidence of galvanic interactions between propagating streaks and connected IMPs is observed. Concurrent in situ open circuit potential (OCP) measurements show a characteristic pattern that correlate with SC initiation, progression, and termination. This work demonstrates the effectiveness of a simple in situ optical-electrochemical setup in tracking dynamic local corrosion processes and directly linking OCP transients to specific corrosion events.

In this work, we study the relationship between the molecular water layer (MWL) and frost freezing onset and propagation. The progression of frost has been reported to be governed by various localized icing phenomena, including interdroplet ice bridging, dry zones, and frost halos. Reports studying the state of water on surfaces have revealed the presence of a thin nanometer water layer on a range of surfaces. Regardless of further investigations that show environmental humidity, temperature, and surface energy to affect the thickness of the MWL on surfaces, the influence of the MWL on frost nucleation and propagation has not yet been previously addressed in the literature. To study the effect of the MWL on surface freezing events, a range of surface-functionalized glass substrates were prepared. In situ monitoring of freezing events with thermal imaging allowed studying the effect of surface chemistry and environmental relative humidity (RH) on the thickness and continuity of the MWL. We argue that the observed icing nucleation and propagation kinetics are directly related to the presence and continuity of the MWL, which can be manipulated by controlling the environmental humidity and surface chemistry.

Understanding how late an inhibitor can be released once corrosion initiated without compromising corrosion protection may help in developing more efficient anticorrosion coatings. We explored this idea through time-controlled Ce(NO₃)₃ availability to AA2024-T3 immersed in 0.05 M NaCl. Ce(NO₃)₃ was supplied at 0, 30, 60, and 180 s from the start of immersion to get a concentration of 0.001 M. Detailed visualization of surface changes at the intermetallic particle level was obtained using in-situ reflected microscopy. SEM-EDX and confocal laser microscopy confirmed the extent of intermetallic degradation and local inhibitor deposition corresponding to operando changes. When the inhibitor is supplied within 60 s of immersion, the surface changes slowdown earlier and are visually less extensive than in uninhibited systems. Furthermore, our results highlight the potential of reflected microscopy for local corrosion inhibition studies and underscore the importance of understanding the interaction between inhibitor release timing and corrosion protection.

Water-borne coatings often contain nanofillers to enhance their mechanical or optical properties. The aggregation of these fillers may, however, lead to undesired effects such as brittle and opaque coatings, reducing their performance and lifetime. By controlling the distribution and structural arrangement of the nanofillers in the coatings and inserting reversible chemical bonds, both the elasticity and strength of the coatings may be effectively improved, while healing properties, via the reversible chemistry, extend the coating’s lifetime. Aqueous dispersions of polymer-core/silica-corona supracolloidal particles were used to prepare water-borne coatings. Polymer and silica nanoparticles were prefunctionalized with thiol/disulfide groups during the supracolloid assembly. Disulfide bridges were further established between a cross-linker and the supracolloids during drying and coating formation. The supracolloidal nanocomposite coatings were submitted to intentional (physical) damages, i.e., blunt and sharp surface scratches or cut through into two pieces, and subsequently UV irradiated to induce the recovery of the damage(s). The viscoelasticity and healing properties of the coatings were examined by dynamic, static, and surface mechanical analyses. The nanocomposite coatings showed a great extent of interfacial restoration of cut damage and surface scratches. The healing properties are strongly related to the coating’s viscoelasticity and interfacial (re)activation of the disulfide bridges. Nanocomposite coatings with silica concentrations below their critical volume fraction show higher in situ healing efficiency, as compared to coatings with higher silica concentration. This work provides insights into the control of nanofillers distribution in water-borne coatings and strategies to increase the coating lifetime via mechanical damage recovery.

The most common way to protect metallic structures from corrosion is through the use of passive and active corrosion protection with coatings containing dispersed corrosion inhibitor particles. Current approaches use inorganic microparticles containing mostly toxic and/or critical elements (e.g. CrVI, Li-salts). Organic inhibitors have been identified as a potential replacement technology due to their high inhibiting efficiency in solution, high versatility and lower toxicity. Nevertheless, when brought into organic coatings these inhibitors lose their efficiency due to unwanted side reactions with the surrounding organic matrix (coating). In this work we propose a novel strategy to isolate the organic corrosion inhibitor microparticles from the surrounding matrix. The new approach is based on the gas-deposition of an oxide nanolayer on the microparticles using gas deposition in a fluidized bed reactor. As a result, the organic particles are better dispersed in the coating and do not react with the surrounding matrix. Upon coating damage the particles are exposed to water and release sufficiently high amounts of the organic corrosion inhibitor at the damaged location. The work introduces a technique that can be used in other applications with similar challenges and a new technology that enables for the first time to store large amounts of active organic corrosion inhibitors in reactive organic coatings for efficient protection of metallic infrastructure. This opens the path to the practical use of highly efficient organic inhibitors in coatings for corrosion protection.

The strategies used by organisms living in water to adhere to surfaces have been a major source of inspiration to develop synthetic underwater adhesives. Amongst the mechanisms explored, byssus-inspired metalorganic chemistry offers a broad range of possibilities due to the breath of coordination bonds, salts and polymer backbones available. This has led to a significant amount of research on bio-inspired synthetic glue-type (liquid) and tape-type (solid) adhesives. However, reversibility under water, durability and universality of adhesion remains elusive. We demonstrate that the combination of Ni-metalorganic chemistry with a flexible hydrophobic polymer allows developing fully healable and recyclable polymers able to reversibly adhere (under water) to substrates with surface energies as diverse as Teflon and glass. Other metal ions such as Fe3+ and Zn2+ did not provide the desired adhesion in water. The underlying mechanism is attributed to local water-induced chain re-orientation and the use of strong but dynamic metalorganic coordination (Ni2+-2,5-thiophenedicarboxaldehyde). The results unveil a versatile route to develop solid-state underwater adhesives and water-triggered healing polymers using a one-pot synthesis strategy (Schiff-base with metal coordination) with an underlying mechanism that can be extrapolated to different application domains such as biomedical, energy and underwater soft robotics.

In this paper, graphene oxide (GO) modified microcapsules have been developed for use in self-healing Cardanol-based epoxy anti-corrosion coatings on steel substrates. The microcapsules had a polymethyl methacrylate (PMMA) shell, covered with aminated GO flakes and contained either of the two complementary healing agents mixed with nanosized GO flakes. One set of capsules contained epoxidized nanosized GO and Cardanol-based epoxy resin, while the other contained aminated nanosized GO and Cardanol-based amine curing agent. The microcapsules had a narrow size distribution with a peak value of 4 μm. The Cardanol-based coatings containing various fractions of up to 20 wt% microcapsules in their stoichiometric ratio showed excellent anti-corrosion and self-healing properties. FT-IR, XPS, AFM, and Raman spectroscopy were used to characterize the size and chemical composition of the GO. Optical microscopy and SEM were used for morphological characterization. Double cantilever test upon bulk samples showed an excellent load transfer across the fracture plane after only 1 day curing at room temperature. The anti-corrosion properties of the Cardanol-based coating containing the two-component microcapsules were tested using electrochemical impedance spectroscopy (EIS). It was found that, after 60-day immersion in 3.5 wt% NaCl solution, the low-frequency impedance modulus |Z|_0.01Hz of the Cardanol-based coating containing GO-modified microcapsules was three orders of magnitude higher than that of the systems with capsules without GO. After scratching the coating containing 20 wt% GO-modified microcapsules and exposing it to an aqueous 3.5 wt% NaCl solution, the |Z|_0.01Hz of the Cardanol-based coating returned over a period of 7 days to the original value.

The interaction of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) with the AA2024-T3 local microstructure (S-phase, secondary phases and matrix) as function of the NaCl concentration is studied. The inhibiting power and the local interaction of DMTD with the metal were studied by in–situ opto-electrochemistry, XPS and Raman spectroscopy. The stability of the inhibiting layers was evaluated by re-exposing the samples to NaCl solutions without inhibitor. The amount of DMTD and its interaction state (chemisorption/physisorption) vary with the local microstructural composition and NaCl concentration. Higher stability of the inhibiting layers is obtained when these are formed in presence of small amounts of NaCl (0.025–0.25 M).

Autonomous through-thickness scratch repair (healing) in coatings requires scratch closure and interfacial molecular sealing. Although qualitative aspects of the first stage of self-healing have been addressed, quantitative description enabling the control over the healing process need further understanding. In this work the polymer-architecture-dependent stored entropic energy during deformation is quantified using the rubber elasticity theory and correlated to the scratch closure degree experimentally observed in microscopic measurements. Using well-defined thermoplastic healing polyurethanes with variable soft phase fraction contents these studies show that pressure-free damage closure of scratches maintaining mechanical integrity during healing is governed by the capability of the polymer to store entropic energy during damage. The storage (and release) of energy is controlled by varying the damage and healing temperatures in relation to the specific viscoelastic length transition (TVLT) and the glass transition temperature (Tg). Damage closure increases linearly with the entropy release and is controlled by two parameters of the network, the junction density and damping factor. If mechanical damage does not lead to storage of mechanical energy healing does not occur.

This work investigates an integrated analysis of in-situ optical data and time-frequency information from electrochemical potential noise (EPN) data to study the effectiveness and durability of an anodic and cathodic corrosion inhibitor. Two different corrosion inhibiting species, cerium(III) (Ce(III)) and phytic acid (PHA), are tested on aluminum alloy AA2024-T3. Corrosion of AA2024-T3 serves as a negative reference. Time-frequency analysis of EPN data provides a direct insight in the kinetics of the electrochemical processes related to different types of corrosion and/or inhibitor activity over time. The simultaneous, in-situ optical technique allows visualizing and quantifying the surface changes associated with the electrochemical signals. Both Ce(III) and PHA were not capable to inhibit corrosion to a large extent, as re-immersion led to electrochemical (corrosion) activity for both inhibitors. Time-variant changes between corrosion, inhibitor activity, inhibited state and re-activation can effectively be discriminated from each other.

In this work a diffusion-driven inhibitor transport model is used to help in the design of inhibitor-loaded carriers for anticorrosive primers. The work focuses on inhibitor release at damaged locations of different dimensions exposed to electrolyte and is validated experimentally. The damage dimensions are first simulated to determine the minimal inhibitor release rate necessary to reach the required inhibitor concentrations for corrosion protection of the exposed metal. Kinematic and mass conservation laws are then used as first-order approximations to study the effect of different characteristics of nano- and micro-particles loaded with inhibitors embedded in an organic coating during the first 100 s of immersion. The simulated results are validated experimentally using epoxy coatings containing cerium-loaded zeolites and diatomaceous earth as nano- and micro-carriers respectively. These experiments confirmed the simulated predictions, showing that under the used exposure conditions nano-particles are only able to protect relatively small damages of micron size dimensions. Micron-sized carriers on the other hand allow sufficient release to protect larger damages, even at lower pigment volume concentrations. Additional simulations on rapid electrolyte diffusion pathways inside the coating are also in good agreement with the experiments, indicating the presence of diffusion pathways might play an important role in sustained inhibitor release and corrosion protection at local damages.

The most widely accepted test for bond durability analysis in aerospace metal-bonded structures is the bondline corrosion test introduced in the late 90s. Little progress has been made however on non-destructive testing methods that allow determining the bond quality after years of use. Here, a non-destructive method based on dielectric spectroscopy is introduced to evaluate the state of a metal-adhesive-metal bond exposed to salt fog spray up to 180 days. Several samples were evaluated with broadband dielectric spectroscopy (BDS), floating roller peel (FRP) tests and bondline corrosion (BLC) after exposure to salt fog spray test for different times. Relaxation processes and conductivity phenomena extracted from the BDS data (e.g. apparent conductivity relaxation time (τ_max) using electric modulus) are found to correlate well with the bond strength measured in peel test and BLC progression. The BDS-based protocol was able to identify the local interfacial degradation stages in a non-destructive mode and with high resolution. The protocol has the potential to be further developed into a test method for durability on coupon level.

A hyphenated optical-electrochemical technique and image analysis protocol is used to quantify global and local (intermetallic) corrosion process and kinetics. Our findings reveal an early stage (< 60 s) composition-dependent hierarchical local activation of all IMs that can be attributed to IM dealloying. This is followed by local trenching initiated at matrix locations adjacent to regions of the IMs previously dealloyed, which in turn develops into concentric trenching around the IMs. These stages have quantifiable activation times and kinetics. While dealloying kinetics are found to be strongly dependent on IM composition and slightly dependent on IM size in the case of the S-phases, trenching kinetics are IM composition and size independent.

The use of self-healing (SH) polymers to make 3D-printed polymeric parts offers the po-tential to increase the quality of 3D-printed parts and to increase their durability and damage toler-ance due to their (on-demand) dynamic nature. Nevertheless, 3D-printing of such dynamic poly-mers is not a straightforward process due to their polymer architecture and rheological complexity and the limited quantities produced at lab-scale. This limits the exploration of the full potential of self-healing polymers. In this paper, we present the complete process for fused deposition model-lingof a room temperature self-healing polyurethane. Starting from the synthesis and polymer slab manufacturing, we processed the polymer into a continuous filament and 3D printed parts. For the characterization ofthe 3D printed parts,we used a compression cut test, which proved useful when limited amount of material is available. The test was able to quasi-quantitatively assess both bulk and 3D printed samples and their self-healing behavior. The mechanical and healing behavior of the3D printed self-healing polyurethane was highly similar to that of the bulk SH polymer. This indicates that the self-healing property of the polymer was retained even after multiple processing steps and printing. Compared to a commercial 3D-printing thermoplastic polyurethane, the self-healing polymer displayed a smaller mechanical dependency on the printing conditions with the added value of healing cuts at room temperature.

The elastic modulus of corrosion product (E_cp) has been reported with significant variations in the literature. This study aims to investigate the E_cp of naturally-generated chloride-induced corrosion products formed in different concrete mixes. Microstructural characterization was conducted through nano-indentation, electron microscopy and Raman spectroscopy. The corrosion products were mainly composed of a goethite matrix with portions of maghemite, independently of the concrete composition. Microscopic analysis suggest that layers of corrosion products grow at different times and under different physico-chemical conditions. Our measurements showed that E_cp varied between 80−100 GPa, which can be suggested for numerical models of corrosion induced cracking.