1,721,023 research outputs found
Selective Polymer Distributed Bragg Reflector Vapor Sensors
No full textWe report on Flory–Huggins photonic sensors for the selective detection of volatile organic compounds without the use of any chemical functionalization. For this purpose, we employed periodic multilayers made of inert cellulose acetate alternated to active polystyrene films whose free volume was modified with silanized ZnO nanoparticles. The simple UV-visible (UV-vis) dynamic optical response of such polymer distributed Bragg reflectors during exposure to vapors of benzene, toluene, o-dichlorobenzene, and carbon tetrachloride allows their detection and recognition based on different chemico–physical affinity with the active polymer medium
Nanoimprint lithography: Toward functional photonic crystals
No full textIn this chapter we review the use of nanoimprint lithography and its derivative soft-lithography techniques for the fabrication of functional photonic crystals. Nanoimprint is a viable, scalable, and cost-effective solution for large area patterning. While initially it relied primarily on pattern transfer from a rigid mold to a thermally softened polymer by embossing, in the last two decades the process evolved rapidly, giving rise to new technologies that allow direct imprint of functional materials such as conjugated polymers, metals, biological matter, and metal oxides. These advancements generated increasing interest in the use of nanoimprint lithography for the fabrication of photonic structures for light management in optoelectronic devices. After describing standard nanoimprint lithography and its derivative soft-lithography methods, we briefly discuss nanoimprint capabilities and prospects in photonic applications. In particular we review recent implementations of imprinted photonic structures for light management in organic light emitting diodes, solar cells, solid state lasers and sensors
Universal Design Rules for Flory–Huggins Polymer Photonic Vapor Sensors
No full textMultilayered photonic sensors that rely on polymer-solvent Flory-Huggins interactions are drawing increasing interest owing to their broad-band selectivity, even among mixtures, without the need for chemical targeting. Moreover, these sensors provide simple colorimetric responses, and easy, quick fabrication both on laboratory and industrial scales. However, complex optical responses and slow response times are limiting their development. In this work, the behavior of different photonic sensor architectures is analyzed to speed up response time and define a strategy to simplify their spectral behavior. To this end, the effect of interfaces, materials order, and thickness on the diffusion kinetics of a single reference analyte in the multilayered sensors is studied to design the optimal structure
A new method for the determination of molecular diffusion coefficient in polymer films by simple UV-VIS spectroscopy
No full textThe possibility to evaluate molecular diffusion coefficient in polymer films directly in-situ is critical to assess barrier properties of packaging systems. Using the polymer packaging itself as smart sensor could lead to increase shelf-life, minimize wastes, and food poisoning effects. In this work we report on a new method that exploit simple UV-Vis spectroscopy to identify diffusion of small molecules in the vapor phase through both commercial polymer packaging systems and into polymer multilayered structures. The new method allows to determine molecular diffusion coefficient values in full agreement with gravimetric data reported in literature
Proline-rich tyrosine kinase 2 and focal adhesion kinase are involved in different phases of platelet activation by vWF
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Into the Blue: Ketene Multicomponent Reactions under Visible Light
No full textFor the first time, a detailed study on the photophysical properties of variously substituted diazoketones and on their photoreactivity under blue LED irradiation was carried out. Despite very limited absorbance in the visible region, we have demonstrated that, independently from their structure, α-diazoketones all undergo a very efficient Wolff rearrangement. Contrarily to the same UV-mediated reaction, where photons can give rise to side processes, in this case, almost all absorbed photons are selective and effective, and the quantum yield is close to 100%. If the rearrangement is carried out in the presence of isocyanides and carboxylic acids/silanols, the photoreactivity is not affected, and the resulting ketenes can afford α-acyloxy- and α-silyloxyacrylamides through two distinct multicomponent reactions, performed both in batch and under continuous flow, with improved selectivity and broader scope. These photoinduced multicomponent reactions can be coupled with other visible-light-mediated transformations, thus increasing the diversity of the molecules obtainable by this approach
Nature-inspired mechanochromic photonic crystals: advancements in distributed Bragg reflectors for strain sensing
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