On the road towards developing truly self-healing polymer coatings, autonomous gap closure behavior is an important step. Stored entropic energy in a polymer could act as driving force for this closure. To make proper use of this concept it is important to develop characterization protocols able to relate entropy release to gap closure dynamics and ultimately to polymer architecture. Dynamic mechanical thermal analysis (DMA) and Laser Speckle Imaging (LSI) have previously been used in separate studies to quantify entropic energy change and measure local polymer dynamics, respectively. This work aims to develop an LSI-based protocol able to relate entropic induced length changes measured in DMA to polymer relaxation dynamics. To this purpose a set of non-healing epoxies with different molecular weight between crosslinks was tested both in DMA and LSI. A recently developed analysis protocol was used to extract, from DMA data, the entropy change at the glass transition region related to displacement (i.e. shape memory effect). With the help of a micro-tensile tester and a temperature control system, LSI allowed quantifying the local dynamics of the studied polymers as function of temperature and strain. The overall relaxation dynamics in stress relaxation tests measured with LSI were then compared to the DMA results. A relation between the strain relaxation dynamics in LSI, crosslinking density, entropy release and tan δ variation with temperature was found. This was done by comparing the frequency and intensity of local displacements measured with LSI to delta length and tan δ obtained with DMA. Furthermore, this research revealed an interesting discrepancy between local strain relaxation and stress relaxation times, as the local strain relaxation time extracted with LSI was shown to be longer than the overall stress relaxation time measured by the micro-tensile tester in the same test. The characterization and data analysis protocol explored here paves the way towards experimental methods that allow a more direct correlation between coating design parameters, such as crosslinking density and chain flexibility, and local entropy driven damage closure.

Alkaline water electrolysis will become increasingly important for supplying the world with sufficient renewable energy, and with raw material for the chemical and pharmaceutical industry. Zero Emission Fuels B.V. (ZEF), a technology start-up based in the Netherlands, is developing a small scale alkaline electrolysis cell (AEC), which is integrated in a methanol producing micro-plant. The challenge of this project is to look into the use of polymers for the encapsulation of the ZEF AEC. The conditions of the ZEF AEC are not to be neglected. The system will run in a 30wt% KOH solution at a temperature of 90 °C and a pressure of 50 bar. Not many polymers will be able to withstand these conditions for a desired lifetime of 20 years. Using CES EduPack, a selection of 30 potentially suitable polymers has been made, from which high density polyethylene (HDPE), 40% glass-reinforced polyphenylene sulfide (PPS-40%gf) and polysulfone (PSU) are further investigated. Based on a literature review and a simple KOH ageing test, HDPE is found unsuitable for application in the ZEF AEC. PPS-40%gf and PSU have been subjected to durability testing for a range of different conditions involving a variety of KOH concentrations (15, 30 and 45wt%), and two oxygen partial pressures (O2 at 5 bar and air with pO2=20%) at different temperatures (90, 120 and 170 °C). The purpose of the ageing experiments is to give a better understanding of the effect of these parameters on the structure and integrity of the polymer; and to eventually be able to acquire a lifetime prediction. Extensive characterisation of the exposed samples has been carried out using different techniques, including weight measurement, tensile testing, DMA, creep-recovery testing, DSC, FTIR, XRD and SEM. After 12 weeks of ageing, it is found that glass-filled polymers are unsuitable for application in a strong alkaline solution at elevated temperatures, due to the dissolution of the glass fibres, which leads to a reduction in mechanical and barrier properties. However, the PPS matrix and PSU are found to be resistant to thermo-oxidative and chemical degradation in the tested ageing conditions. Only subtle changes in mechanical, visco-elastic and thermal behaviour are observed, which can be assigned to the effects of physical ageing. Due to the undesirable brittle nature of PPS, it can be concluded that PSU is the most promising candidate for the long-term application in alkaline electrolysis.

Coating deposition by Physical Vapour Deposition (PVD) on high strength steels is an important research project at TATA Steel - IJmuiden. The research is aimed at replacing the conventional hot-dip galvanisation process to obtain a defect-free coating without affecting their well-engineered properties. However, the annealing treatment of the steel, performed to obtain these properties, affects the coating adhesion properties. This is a result of the selective oxidation process, which forms external oxides of alloying elements at the surface. Therefore, a pre-treatment process is required to remove these surface oxides from the steel strips before they are coated. Plasma sputtering is currently being used for the pre-treatment to remove any contaminants and surface oxides from the steel. To obtain a good coating adhesion, a relatively large amount of surface oxides needs to be removed by sputtering. Also, the removed material is known to contaminate the vacuum chamber in the PVD deposition line, for which frequent maintenance of the chamber might be necessary. Thus, an additional surface pre-treatment step was investigated in this study to reduce the sputtering process inside the vacuum as much as possible. In the present work, the effect of both direct current electrolytic alkaline cleaning and sulphuric acid etching on the surface of DP800 steel was investigated. Two different baths were considered for this purpose; a 27 g/L NaOH bath with some additive at 60°C and a 50 g/L H2SO4 bath at 25°C and 50°C. A current density of 1.5 A/dm2 was applied during the electrolytic cleaning for which both cathodic and anodic polarisation methods were investigated. Also, a range of acid etching times (10s to 120s) was investigated for the given concentration and temperatures of the acid bath to study its effect on the surface. The effect of adding a corrosion inhibitor into the acid bath on the rest of the coating deposition process was also investigated. Various surface characterisation techniques and wettability tests were performed to study the changes in morphology and composition of the surface and their effect on the coating adhesion properties of the treated samples. Finally, coating adhesion tests were performed after zinc deposition to investigate the adhesion performance of the steel after the pre-treatment steps. Initial surface analysis during electrolytic alkaline cleaning showed that the anodic polarisation was more effective than cathodic polarisation of the sample, as the latter tends to reduce the surface wettability by additional deposits of iron fines over the surface. A subsequent acid etching provided a reduction in the minimum required sputter intensity to obtain a good adhesion from 2300 kJ/m2 to about 800 kJ/m2. A further reduction was achieved to a sputter intensity of only 214 kJ/m2 after retarding the effects of surface reoxidation by vacuum sealing the samples. Acid etching at 25°C provided bad coating adhesion at lower etching times, attributed to the partial dissolution of surface oxides and absence of an initial grain roughening. Good coating adhesion was either obtained at higher etching times or by increasing the temperature of the acid bath to 50°C. Addition of a corrosion inhibitor was considered impractical as high sputter intensities (> 321 kJ/m2) was required to remove the adsorbed inhibitor molecules from the surface. Thus, a reduction in the required sputter intensity was achieved by more than a factor of 10 after acid etching, only if the effects of surface reoxidation during the transfer time between acid etching and entering the PVD installation can be minimized.

Self-healing ability in polymers is typically probed by monitoring restorative properties after localized macroscopic damage or repetitive cycles of destructive testing followed by a healing cycle (e.g. cut-and-heal tests). However, the restoration of homogeneously distributed damage before ultimate failure remains largely unattended in literature. This work investigates whether damage degree and damage restoration after plastic deformation in self-healing polymer networks can be identified via continuous relaxation spectra from rheology, which were recently successfully employed to identify energy contributions in self-healing polyurethanes. As a model system a self-healing epoxy-silane dual network with dynamic sulfur-sulfur bonds is used together with a non-healing reference epoxy. Three levels of deformation are probed: pristine, partially plastic (near yield), and fully plastic (near failure). Compared to the non-healing reference epoxy, the self-healing epoxy is observed to have faster dynamics of the main relaxation peak and to dissipate more energy at very fast (10-9 s) relaxation times. It is found that any level of plastic deformation (near yield or near failure) induces clear changes in the energy profile compared to the pristine state (e.g. relaxation peak height drop). Between the two levels of plastic deformation, no clear distinction could be made. An oven treatment, intended to repair any induced damage by stimulating network mobility through sulfur-sulfur bond reshuffling above Tg, was found to shift the energy profile to longer relaxation times for both pristine and plastically deformed samples not observed in the non-healing polymer. However, this time shift could be undone by allowing a one week recovery period after the oven treatment. It is proposed that the observed behavior can be explained by trapping, in self-healing polymers, a non-equilibrium polymer state through quenching. Despite the necessary further research, the results confirm the potential of continuous relaxation spectra to evaluate damage degree and damage restoration in plastically deformed self-healing polymers.

Filamentous fungi grow large networks of biomass with minimal energy input. This biomass consists of polysaccharide-based filamentous networks and adherent extracellular polymeric substances (EPS). Recent reports show that this biomass can be formed into plastic-like thin film materials. Further, non-filamentous fungi have been applied as living coatings on wood. Even so, filamentous fungi remain unexplored for coating applications. This work fills that gap by studying how a selected filamentous fungus (Schizophyllum commune) and its lab-produced biomass interact with aerospace aluminum alloys, and to explore their potential as a sustainable resource to create coatings. Two complementary routes were explored in this work. In the first one, S. commune was allowed to grow—under controlled conditions—on the surface of bare aluminum alloys of different compositions and surface treatments. The growth extent, filament density, and structure were investigated as a function of the underlying metal composition, surface treatment, and nutrient availability. In the second route, thin-film coatings were produced from processed biomass extracted from liquid cultures of S. commune. The quality of the consolidated films and their scratch resistance and adhesion as a function of a range of processing parameters and aluminum surface treatments was investigated. S. commune grew further and more densely on AA6082 than on AA2024 and AA7075. Differences decreased after grinding, which suggests that the alloy-dependent near-surface deformed layer and alloy composition heavily influence fungal growth. The in-situ-grown fungi led to intense local surface corrosion and weakly adhered biomass. Alternatively, films produced from processed liquid culture biomass led to semi-transparent coatings with microstructure dependent on the processing conditions and fungal extract used. Although processing steps led to improvements in scratch resistance and porosity, coating macroporosity remained high and insufficient for barrier requirements. Surface treatments led to clear improvements, but even then, film adhesion remained well below that of more broadly studied and developed biopolymer coatings (>10x better adhesion). This research showed the potential of fungi to create films on aluminum alloys with ample room for improvement toward fungi-based coatings. Future research should focus on more extensive species screening, adhesion optimization, decreasing porosity, and better understanding fungi-metal local interactions.

Microbes, and the biofilms they form on surfaces, generally have a negative impact on performance. Well­-known examples are the increase of drag in ships and pipes, and the accelerated corrosion of metallic structures known as MIC. Among microbes, diatoms form a large unicellular algae group known to play a relevant role in the first stages of biofilm formation. Diatoms are well-­known for their species­-dependent silica exoskeletons, but they also produce, as other microbes, extracellular polymeric substances (EPSs) that may offer opportunities for the development of novel bio­based surface treatments. In this work we studied the interaction between a marine diatom species named Cylindrotheca fusiformis and aerospace aluminum alloys as a first step towards novel surface protection treatments of aircraft structures. Two routes were followed to study the interaction of C. fusiformis with aluminum alloys after studying diatom population growth. The first route focused on the biofilm formation on aluminum 99.5%, AA20204-­T3 and AA7075­-T6 to study the effect of surface composition. The effect of the surface preparation (degreased vs. polished) was then studied with AA2024­T3 substrates. The second route focused on the study of diatoms’ motility on aluminum 99.5% and AA2024-­T3 with various surface pretreatments. In this work, a number of characterization techniques such as FTIR, SEM/EDS, Raman spectroscopy and image correlation techniques were used. It was found that C. fusiformis forms well­-adherent biofilms on all aluminum substrates, independently of the surface composition and surface pre­treatment. Nevertheless, the biofilms appeared to be most homogeneous on AA7075­T6, while the EPS layer was more homogeneous on aluminum 99.5% and AA2024­T3. The motility studies showed that C. fusiformis lowers its surface motility rapidly when on aluminum 99.5% until cells stop being motile. On AA2024­T3, cells maintain their motility for longer periods of time. The motility dependency on surface chemistry is hypothesized to come from speciation dependent aluminum toxicity. Post­mortem chemical analysis of the exposed surfaces showed traces of organic material in the form of proteins and carbohydrates attributed to displacement trails. The results confirm that monocultures of C. fusiformis are able to generate biofilms on aerospace aluminum alloys and release water­ insoluble organic matter on the surface. The promising results here obtained pave the way for more dedicated research to understand the relationships between surface chemistry and topology, and diatom motility and biofilm formation and composition.