Large-area wet-chemical deposition of nanoporous tungstic silica coatings

We report on a facile procedure for synthesis of nanoporous coatings of tungstic silica through wet-chemical deposition and post-treatment of tungsten-doped potassium silicate solutions. The process relies on an aqueous washing and ion exchange step where dispersed potassium salt deposits are removed from a 150 nm silicate gel layer. Through an adjustment of the pH value of the washing agent within the solubility regime of a tungstic salt precursor, the tungsten content of the remaining nanostructured coating can be controlled. We propose this route as a universal approach for the deposition of large-area coatings of nanoporous silica with the potential for incorporating a broad variety of other dopant species. As for the present case, we observe, on the one hand, antireflective properties which enable the reduction of reflection losses from float glass by up to 3.7 percent points. On the other hand, the incorporation of nanoscale tungstic precipitates provides a lever for tailoring the coating hydrophilicity and, eventually, also surface acidity. This may provide a future route for combining optical performance with anti-fouling functionality

Thermal strengthening of low‐expansion glasses and thin‐walled glass products by ultra‐fast heat extraction

Thermal strengthening remains the primary method for enhancing the practical strength of commodity glass products, however, the process is limited in terms of applicable glass thickness and coefficient of thermal expansion. The primary reasons for this limitation are the achievable heat transfer coefficient when using conventional gas cooling, and the occurrence of transient surface tension in the early stages of rapid quenching. We revisit this problem for the case of thin borosilicate glass sheet. Using liquid gallium as the cooling medium, ultra‐fast heat extraction is achieved, with a heat transfer coefficient exceeding 5000 Wm −2 K −1 . The low vapor pressure of gallium even at high temperatures enables preheating to a wide range of sheet entrant temperatures. We demonstrate thermal strengthening of low‐expansion borosilicate glass with persistent surface compression of up to 85 MPa, and quenching to a fictive temperature of ~190 K above the glass transition temperature. Glass sheet obtained in this way exhibits notably enhanced surface defect resistance to sharp indentation. In addition to thermal strengthening, the extraordinarily high heat extraction rates achieved by liquid metal immersion enable exploitation of high‐ T f glass properties beyond small and thin sample geometry

Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12–14% of spiropyran at the silica–water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film’s conformational state, which affects its subsequent response behavior

Strain-rate sensitivity of glasses

AbstractWe report on the loading-rate dependence of localized plastic deformation in inorganic covalent, metallic, ionic and superionic glasses. For this, the strain-rate sensitivity is determined through instrumented nanoindentation in a load-controlled strain-rate jump test. Through relating the strain-rate sensitivity to the reduced temperature, the packing density, the network dimensionality and the average single bond strength of the system, a qualitative mechanistic description of the strain-mediating process is possible. A strong variability of strain-rate sensitivity is obtained only at intermediate values of packing density, network connectivity or bond strength, when other parameters such as chemical composition and specific structural arrangement are dominating the deformation process. On the other side, for high bond strength and connectivity or for high packing density, the strain-rate sensitivity of the considered glasses is always low, which is also confirmed through the dependence of strain-rate sensitivity on Poisson ratio. Here, only for glasses with a Poisson ratio of ~0.3–0.4 we observe a wide variability of the loading-rate dependence of local deformation. For higher or lower Poisson ratio, the observed dependence is always low: when the limiting factor in deformation is primarily network connectivity and bond strength or packing density, respectively, once an activation barrier is overcome, deformation is only weakly loading-rate-dependent. This is regardless of the height of the activation barrier. When approaching the glass transition temperature, high strain-rate sensitivity is observed only in glasses where non-Newtonian flow is expected also in the corresponding liquid

Boson peak, heterogeneity and intermediate-range order in binary SiO2-Al2O3 glasses

In binary aluminosilicate liquids and glasses, heterogeneity on intermediate length scale is a crucial factor for optical fiber performance, determining the lower limit of optical attenuation and Rayleigh scattering, but also clustering and precipitation of optically active dopants, for example, in the fabrication of high-power laser gain media. Here, we consider the low-frequency vibrational modes of such materials for assessing structural heterogeneity on molecular scale. We determine the vibrational density of states VDoS g(ω) using low-temperature heat capacity data. From correlation with low-frequency Raman spectroscopy, we obtain the Raman coupling coefficient. Both experiments allow for the extraction of the average dynamic correlation length as a function of alumina content. We find that this value decreases from about 3.9 nm to 3.3 nm when mildly increasing the alumina content from zero (vitreous silica) to 7 mol%. At the same time, the average inter-particle distance increases slightly due to the presence of oxygen tricluster species. In accordance with Loewensteinian dynamics, this proves that mild alumina doping increases structural homogeneity on molecular scale

Synthesis, characterization and properties of novel photoactive polysaccharides

In this work it was illustrated how light can be applied as probe for the analytics of the structure of complex polysaccharide derivatives and how to implement photoactivity to polysaccharides by chemical modification. The photochemistry of the new derivatives was studied in the dissolved state as well as in nanoparticulate systems. Moreover, insights in the morphology of nanoparticles prepared from hydrophobic polysaccharide derivatives were gained.Im Rahmen der vorliegenden Arbeit wurde gezeigt wie Licht einerseits als Sonde für die Charakterisierung der Struktur komplexer Polysaccharidderivate genutzt werden kann und wie andererseits photoaktive Polysaccharidderivate durch chemische Modifizierung erhalten werden können. Die Photochemie der neuen Derivate wurde sowohl in Lösung als auch in Nanoparikeln untersucht. Darüber hinaus wurden neue Erkenntnisse über die Morphologie von Nanopartikeln gewonnen, die aus hydrophoben Polysaccharidderivaten hergestellt werden können

Angular scattering pattern of femtosecond laser‐induced refractive index modifications in optical fibers

Abstract Focused femtosecond laser irradiation is used to induce light scattering modifications in the core of an optical fiber. This turns the fiber into a diffuse, line‐shaped light source. The scattering is investigated by imaging almost the full solid angle far‐field pattern for the first time. Additionally, an electromagnetic scattering model is developed to explain the observations. The findings herein change how the relationship between light scattering and the refractive index fluctuations is perceived by showing that the far‐field scattering pattern is the power spectral density of the polarization current inside the scattering center. Further, the authors contribute to a better estimation of the scattering process by showing that the total scattering power scales quadratically with the laser‐induced refractive index change and its volume

Mehrsprachigkeit und Interkulturalität im Kindergarten

In Niederösterreich leben über 6.000 Kinder mit einer anderen Muttersprache als Deutsch. Die Landesregierung reagierte darauf und entwickelte für den Bereich Kindergarten ein eigenes Interkulturelles Konzept („Interkulturelle Mitarbeiter und Mitarbeiterinnen“), wodurch Kinder sprachlich intensiver gefördert werden und ein bewusster interkultureller Austausch stattfindet. In der vorliegenden Arbeit steht eine Fallstudie eines mehrsprachigen und multikulturellen Landeskindergartens, in dem wöchentlich einmal eine Interkulturelle Mitarbeiterin arbeitet, als Exempel im Mittelpunkt. Dieser lagen primär folgende Fragestellungen zugrunde: Wie werden Mehrsprachigkeit und Interkulturalität in der Institution sichtbar gemacht? Welche Rollen haben die Kindergartenpädagogin, die Kinderbetreuerin und die Interkulturelle Mitarbeiterin inne? Zu Beginn im theoretischen Teil wurden die Termini Mehrsprachigkeit und Interkulturalität genauer diskutiert. So wurden einerseits Sprache und Identität sowie die Sprachenpolitik und andererseits die Interkulturelle Erziehung näher beleuchtet. Im nächsten Teil lag besonderes Augenmerk auf die Rahmenbedingungen der Institution Kindergarten. Es wurde das niederösterreichische Kindergartengesetz sowie das Interkulturelle Konzept in Niederösterreich analysiert. Der Landeskindergarten selbst stand im Anschluss im Mittelpunkt. Anhand von Beobachtungen, Interviews und diversen Dokumenten wurden die Bereiche Räumlichkeit als Platz für Mehrsprachigkeit und Interkulturalität, Gruppenkonstellation, Sprachverwendung, Interaktionen mit dem Kindergartenpersonal und interkulturelle und mehrsprachige Aktivität untersucht. So konnte zusätzlich mit Hilfe von Fachliteratur ein detailiertes Bild zu Mehrsprachigkeit und Interkulturalität im Landeskindergarten geliefert werden. Aus den Ergebnissen der Untersuchung ließen sich Forderungen in erster Linie an die politischen Verantwortlichen stellen, die im Schlusskapitel detailiert ausformuliert wurden

Plasticity, crack initiation and defect resistance in alkali-borosilicate glasses: From normal to anomalous behavior

We provide a comprehensive description of the defect tolerance of sodium-borosilicate glasses upon sharp contact loading. This is motivated by the key role which is taken by this particular glass system in a wide variety of applications, ranging from electronic substrates, display covers and substrates for biomedical imaging and sensing to, e.g., radioactive waste vitrification. The present report covers the mechanical properties of glasses in the Na2O–B2O3–SiO2 ternary over the broad range of compositions from pure SiO2 to binary sodium-borates, and crossing the regions of various commercially relevant specialty borosilicate glasses, such as the multi-component Duran-, Pyrex- and BK7-type compositions and typical soda-lime silicate glasses, which are also included in this study. In terms of structure, the considered glasses may be separated into two groups, that is, one series which contains only bridging oxygen atoms, and another series which is designed with an increasing number of non-bridging oxygen ions. Elastic moduli, Poisson ratio, hardness as well as creep and crack resistance were evaluated, as well as the contribution of densification to the overall amount of indentation deformation. Correlations between the mechanical properties and structural characteristics of near- and mid-range order are discussed, from which we obtain a mechanistic view at the molecular reactions which govern the overall deformation reaction and, ultimately, contact cracking