How thermal curing of an organic paper coating changes topography, chemistry, and wettability

Celluloses are preferred renewable substrates, but hydrophilicity and porosity disfavor their water resistance. We present here an ecofriendly application of imidized nanoparticles and a method to flexibly tune the surface wettability of papers. The soft nanostructured coating is sensitive to thermal curing, which affects both the surface chemistry and morphology. The thermal stability of the coating is first investigated with conventional and modulated differential scanning calorimetry, revealing influences of the imide content and an endotherm reaction below the glass transition temperature at 120-150 °C. The latter is studied in detail for an appropriate selection of the copolymer precursors. According to diffuse reflection infrared spectroscopy, Raman spectroscopy, and UV/vis spectroscopy, the endotherm corresponds to an imidization reaction. The morphology of the coatings is followed at various scale levels by contactless roughness measurements and atomic force microscopy. Finally, the experimental values are fitted to the parameters of the Wenzel wetting model, and so-called calibration curves for the relation between contact angles, surface roughness, and surface chemistry are presented. They allow the prediction of the water contact angle of coated papers from the hydrophilic to the hydrophobic range, with a maximum in hydrophobicity after increasing the imide content at 120-150 °C curing.     

Additive-free clicking for polymer functionalization and coupling by tetrazine-norbornene chemistry

Herein we report the use of a tetrazine-norbornene inverse electron demand Diels-Alder conjugation applied to polymer end-functionalization and polymer-polymer coupling. The reaction was found to be applicable to polymer-polymer coupling, as judged by SEC, DOSY NMR, and LCxSEC analyses, giving diblock copolymers by merely mixing the constituent homopolymers together under ambient conditions, using no catalyst, additive, or external stimulus.     

Quantitative analysis of Mo–Si–B alloy phases with wavelength dispersive spectroscopy (WDS–SEM)

Mo–Si–B alloys show great potential as high temperature materials. Due to peak overlapping of B‐K_α and Mo‐M_ζ, analyzing these alloys with microanalysis presents a real challenge. This paper describes the analytical methodology used to qualify and quantify the boron content in these alloys without stoichiometric reference samples by the use of a single parallel‐beam wavelength dispersive spectrometer. Characterization of boron is performed by using a coupled energy dispersive X‐ray spectroscopy—wavelength dispersive spectroscopy system in a scanning electron microscope. Self‐made pure element samples are used for calibration and quantification of the boron content.     

Unusual coordination behavior of Cr3+ in microporous aluminophosphates

A CrAPO-5 molecular sieve has been investigated with X-ray absorption spectroscopy (EXAFS-XANES) as dehydrated material and after loading with water and ammonia to unravel the coordination geometries of Cr3+ in the framework of a microporous crystalline aluminophosphate, more particularly of the AFI-type. A comparison of the XANES data, a preedge analysis with crystal field multiplet calculations and EXAFS data, pointed toward the presence of framework Cr3+ which, on dehydration, takes on a distorted tetrahedral coordination state. Due to the 3d3 configuration of Cr3+, this unusual tetrahedral coordination environment strongly tends to transform into the more stable 6-fold coordination geometry by binding two extraframework water molecules during hydration. In the presence of ammonia, tetrahedral Cr3+ readily transforms into a 5-fold coordination geometry by binding one ammonia molecule. Therefore, depending on the environmental conditions, the Cr3+ ions can occur in a 4-, 5-, or 6-fold coordination. This observation underlines the flexibility of transition metal ions, such as Cr3+, to cope with unusual coordination geometries in inorganic hosts, making them interesting as potential active sites in heterogeneous catalysis.     

The improper infinite derivatives of Takagi's nowhere-differentiable function

Let T be Takagi's continuous but nowhere-differentiable function. Using a representation in terms of Rademacher series due to N. Kono [Acta Math. Hungar. 49 (1987) 315-324], we give a complete characterization of those points where T has a left-sided, right-sided, or two-sided infinite derivative. This characterization is illustrated by several examples. A consequence of the main result is that the sets of points where T^′(x)=±∞ have Hausdorff dimension one. As a byproduct of the method of proof, some exact results concerning the modulus of continuity of T are also obtained.     

Atomic scale Kelvin probe force microscopy studies of the surface potential variations on the TiO2(110) surface

From an interplay of simultaneous Kelvin probe force microscopy and noncontact atomic force microscopy we study atomic-scale variations in the electronic surface potential on TiO(2)(110). Both imaging channels reveal an atomic contrast reflected by the geometry and charged state of the alternating rows of Ti and O surface atoms. From a thorough cross-section analysis we add significant trust to the concept of a local contact potential difference, and determine from this the chemical identity of individual surface species and their role in setting up the local surface potential.