NMR Study of the Microstructures and Water–Polymer Interactions in Cross-Linked Polyurethane Coatings

The microstructure of a polymer coating plays an important role in the water uptake behavior. This paper aims to correlate the molecular mobility and the water–polymer interactions with the microstructures of a highly cross-linked PU system. GARfield NMR imaging was used to monitor in situ the water uptake of the PU coating at different temperatures. The results of continuum <i>T</i>₂ fitting show that at temperatures below the enthalpy relaxation temperature (65 °C) the PU coating uptakes water, whereas the polymer matrix is not plasticized by the presence of water. At higher temperatures, however, the polymer matrix is significantly mobilized by the presence of water molecules as indicated by the appearance of the longer <i>T</i>₂ component. The water content in the PU coating is monitored by GARfield NMR at different temperatures. The results show that the water content decreases in two steps as the temperature decreases from 85 °C to the room temperature. This result is explained in combination with the molecular relaxation phenomenon probed by the DSC. A microstructure model was formulated based on the experimental results

High spatial resolution NMR imaging of polymer layers on metallic substrates

High spatial resolution NMR imaging techniques have been developed recently to measure the spatial inhomogeneity of a polymer coating film. However, the substrates of the polymer coatings for such experiments are generally required to be non-metallic, because metals can interact with static magnetic fields B(0) and RF fields B(1) giving rise to artifacts in NMR images. In this paper we present a systematic study on the effects of metallic substrates on 1D profiles obtained by high resolution NMR imaging. The off-resonance effect is discussed in detail in terms of the excitation profile of the RF pulses. We quantitatively show how the NMR signal intensities change with frequency offset at different RF pulse lengths. The complete NMR profiles were simulated using a Finite Element Analysis method by fully considering the inhomogeneities in both B(1) and B(0). The excellent agreement between the calculated and measured NMR profiles on both metallic and non-metallic substrates indicates that the experimental NMR profiles can be reproduced very well by numerical simulations. The metallic substrates can disturb the RF field of the coil by eddy current effect and therefore change the NMR profiles. To quantitatively interpret the NMR profile of a polymer layer on a metallic substrate, the profile has to be divided by the profile of a reference on the same metallic substrate located at the same distance from the coil

Aureobasidium melanogenum: a native of dark biofinishes on oil treated wood

The genus Aureobasidium, which is known as a wood staining mould, has been detected on oil treated woods in the specific stain formation called biofinish. This biofinish is used to develop a new protective, self-healing and decorative biotreatment for wood. In order to understand and control biofinish formation on oil treated wood, the occurrence of different Aureobasidium species on various wood surfaces was studied. Phenotypic variability within Aureobasidium strains presented limitations of morphological identification of Aureobasidium species. PCR amplification and Sanger sequencing of ITS and RPB2 were used to identify the culturable Aureobasidium species composition in mould stained wood surfaces with and without a biofinish. The analysed isolates showed that several Aureobasidium species were present and that Aureobasidium melanogenum was predominantly detected, regardless of the presence of a biofinish and the type of substrate. A. melanogenum was detected on wood samples exposed in the Netherlands, Cameroon, South Africa, Australia and Norway. ITS-specific PCR amplification, cloning and sequencing of DNA extracted from biofinish samples confirmed results of the culturing based method: A. melanogenum is predominant within the Aureobasidium population of biofinishes on pine sapwood treated with raw linseed oil and the outdoor placement in the Netherlands

Elucidating the Dehydration Pathways of K₂CO₃·1.5H₂O

Potassium carbonate sesquihydrate has previously been identified as a promising material for thermochemical energy storage. The hydration and cyclic behavior have been extensively studied in the literature, but detailed investigation into the different processes occurring during dehydration is lacking. In this work, a systematic investigation into the different dehydration steps is conducted. It is found that at higher temperatures, dehydration of pristine material occurs as a single process since water removal from the pristine crystals is difficult. After a single cycle, due to morphological changes, dehydration now occurs as two processes, starting at lower temperatures. The morphological changes open new pathways for water removal at the newly generated edges, corners, and steps of the crystal surface. The observations from this work may contribute to material design as they elucidate the relation between material structure and behavior

The indoor fungus Cladosporium halotolerans survives humidity dynamics markedly better than Aspergillus niger and Penicillium rubens, despite less growth at lowered steady state water activity

Indoor fungi cause damage in houses and are a potential threat to human health. Indoor fungal growth requires water, for which the terms water activity (aw) and relative humidity (RH) are used. The ability of the fungi Aspergillus niger, Cladosporium halotolerans, and Penicillium rubens in different developmental stages to survive changes in aw dynamics was studied. Fungi grown on media with high aw were transferred to a controlled environment with low RH and incubated for one week. Growth of all developmental stages was halted during incubation below 75 % RH, while growth continued at 84 % RH. Swollen conidia, germlings, and micro-colonies of A. niger and P. rubens could not reinitiate growth when retransferred from a RH below 75 % to high aw All developmental stages of C. halotolerans showed growth after retransfer from 75 % RH. Dormant conidia survived retransfer to a medium with high aw in all cases. In addition, retransfer from 84% RH to high aw resulted in burst hyphal tips in Aspergillus and Penicillium Cell damage of hyphae of these fungi after incubation at 75 % RH was already visible after 2 hours of incubation as observed by staining with the fluorescent dye TOTO-1. Thus, C. halotolerans is more resistant to aw dynamics than A. niger and P. rubens, despite its limited growth, compared to these fungi, at a lowered steady state aw The survival strategy of this phylloplane fungus to these dynamics in aw is discussed in relation to its morphology as studied with Cryo-SEM. SOCIETAL IMPORTANCE: Indoor fungi cause structural and cosmetic damage in houses and are a potential threat to human health. Growth depends on water, only available at certain periods of the day (e.g cooking, showers). To know why fungi can or cannot survive indoors is important to find novel ways for prevention. Until now the ability of fungi to grow on media with little available water at a steady state (unchanging conditions) is important to evaluate whether a fungus could grow indoors. In this study, we found that the fungus Cladosporium halotolerans, a common indoor fungus, is more resistant to changes in available water than the fungi Aspergillus niger and Penicillium rubens despite the fact that the latter fungi can grow on media with low available water. Concluded, the ability of fungi to deal with changes in humidity is at least as important as the ability to grow at low water media