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Aqueous processes yielding hybrid or composite materials are widespread in natural environments and their control is fundamental for a multiplicity of living organisms. Their design and in vitro engineering require knowledge about the spatiotemporal evolution of the interactions between the involved liquid and solid phases and, especially, the interphases governing the development of adhesion during solidification. The present study illustrates the effects of distinct proteins on the precipitation of sodium chloride encompassing the size, shape and distribution of halite crystals formed during the drying of droplets containing equally concentrated saline protein solutions. The precipitates obtained from aqueous sodium chloride formulations buffered with tris(hydroxymethyl)aminomethane (Tris) contained either bovine serum albumin (BSA), fibrinogen or collagen and were characterized with respect to their structure and composition using optical and electron microscopy as well as x-ray analysis. The acquired findings highlight that depending on the protein type present during droplet drying the halite deposits predominantly exhibit cubic or polycrystalline dendritic structures. Based on the phenomenological findings, it is suggested that the formation of the interphase between the growing salt phase and the highly viscous saline aqueous jelly phase containing protein governs not only the material transport in the liquid but also the material exchange between the solid and liquid phases.

The effect of the pre-bond contamination with fingerprint (FP), both during the production and the application of adhesively bonded patch repairs on composite aircraft parts, and the cumulative effect of fingerprint and hygrothermal ageing on the fracture toughness of carbon fiber reinforced plastic (CFRP) bonded joints are experimentally investigated. To this end, mode I and mode II fracture toughness tests were conducted on FP contaminated coupons and mode II fracture toughness tests on FP contaminated and aged coupons. The artificial FP was supposed to mimic the accidentally applied fingerprints on the CFRP adherent and was applied on the adherent in the size of a human thumb. The two investigated FP formulations consisted of an artificial hand perspiration solution for the production scenario, and of Skydrol hydraulic-oil for the repair scenario. Three levels of contamination with FP were considered for each scenario. The hygrothermal ageing conditions applied until moisture saturation achieved were 70 °C/ 85% RH. Prior to bonding, the CFRP adherent surfaces were inspected using full-scale monitoring with optically stimulated electron emission (OSEE), an extended nondestructive testing method, in order to analyze the physicochemical variations at the contaminated surface of the adherents before bonding. The ANOVA statistical method was used to assist the evaluation of the results and the deduction or reliable conclusions. The results revealed that the pre-bond FP contamination of the adherents leads to the reduction of the fracture toughness of the CFRP bonded joints. After-bond hygrothermal ageing under the prescribed conditions had no significant influence on the moisture absorption and load carrying capacity of the joint. However, it influenced the bondline integrity as it led to a significant reduction of the fracture toughness of the joint. The effect of the combination of pre-bond contamination and after-bond hygrothermal ageing is more severe than the two separate effects.

Classical molecular dynamics were carried out in order to obtain insights into proper conditions to perform chemical fixation of carbon dioxide (CO2) with epoxide molecules into cyclic carbonates. Two different molecules containing epoxide groups were investigated: 1,2–Epoxybutane (EB), called linear aliphatic epoxide molecule, and 3-Ethyl-7-oxabicyclo(4.1.0)heptane (EC), called cycloaliphatic epoxide molecule. The reaction systems involving carbon dioxide additionally were catalyzed by tetraethylammonium bromide (TEAB). The dynamics of the molecular groups were studied by taking into account known reaction mechanisms to investigate whether the optimal reaction conditions were observed. Radial distribution functions and self-diffusion coefficients were calculated and revealed that in case of the systems with cycloaliphatic epoxide groups as reagent the CO2 molecules were located far away from the agglomerate formed by the dispersed tetraethylammonium bromide catalyst and epoxide groups (EC), and they do not present enough mobility to overcome the long distances to react. Additionally, it was observed that, in the case of the linear aliphatic epoxide groups (EB), the dynamics of the groups tends to facilitate the reaction mechanisms by presenting a considerable amount of available CO2 molecules in the neighborhood of the epoxy rings. Thus, via the Molecular Dynamics insights, the systems containing linear aliphatic epoxide groups presented a much more accessible condition for the subsequent reaction steps of the carbon dioxide fixation to occur as compared to systems containing cycloaliphatic epoxide groups. The simulation results are in agreement with the experimental findings, which showed via infrared spectroscopy the successful conversion of epoxy rings from linear aliphatic epoxide molecules into five-membered cyclic carbonates after reacting with carbon dioxide.

Assessing adhesion or strength of composites or adhesive joints in a non-destructive way is highly challenging. Therefore, instead of performing retrospective quality assurance, i.e. investigating manufactured joints, it is advantageous to safeguard performance and quality of each layer and each interface already during manufacture. This approach still is challenging, as it requires a systematic quantitative evaluation of threshold criteria, but appreciably it gets more and more feasible. We present approaches for an inline-capable and non-destructive quality assurance of steps in manufacturing processes used for tailoring the state of substrate surfaces. Benefits from applying techniques for inline surface analysis like Optically Stimulated Electron Emission (OSEE) and Aerosol Wetting Test (AWT) will be detailed. The performed procedures contribute to a novel class of non-destructive testing (NDT) techniques, classified as Extended NDT (ENDT). The principle of ENDT methods is based on the detection of selected physico-chemical properties which are important for the anticipated performance of the functional interfaces in the products to be manufactured. A prerequisite for obtaining reliable composite materials is to reproducibly prepare a suitable surface state of the substrates before the first step of a coating or bonding process. As demonstrative application scenarios, we highlight first an exemplary surface pretreatment process for steel substrates, and second the identification of a surface state for carbon fiber reinforced polymer (CFRP) adherents suitable for joining. Concerning steel substrates we investigated two types of steel both in the as-received state and a state after grinding. We demonstrate that the removal of the topmost material layer comprising the reaction layer and mechanically deformed metal grains strongly affects the properties of the resulting adherent surface. As a consequence, a material-specific time slot for a steel substrate exposure in air after grinding is suggested in which the surface properties probed by OSEE remain unchanged. Moreover, we work out that the sensitivity and accuracy of inline-capable NDT techniques allow distinguishing surface states suitable for bonding of CFRP adherents from surface states unfavourable for adhesive bonding, and we exemplarily verify this statement for bonding processes applying freshly ground CFRP or, respectively, CFRP covered with thin layers of release agents.