Ozone layer

Summary

The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately above Earth, although its thickness varies seasonally and geographically. The ozone layer was discovered in 1913 by French physicists Charles Fabry and Henri Buisson. Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of , except that there was no radiation below a wavelength of about 310 nm at th

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We investigate in this work the fabrication of polymer micro-fluidic and micro-mechanical devices based on sublimable compounds as sacrificial layers, using a thick-film screen-printing deposition process. Fabrication of printed polymer microstructures featuring properties such as low cost, transparency and biocompatibility is particularly attractive and suitable for disposable biomedical devices. Channel, cavities and spacings for micro-devices are first defined by sacrificial material layers. This is followed by polymer resin deposition and polymerization. Removal of the sacrificial layers is then accomplished by heating at their decomposition / evaporation / sublimation temperature (Fig 1). This process does not require an ulterior dissolution step, and systems exist where the sacrificial layer molecules escape by diffusion through the polymer at high temperature: we are therefore not limited to open structures. Furthermore, the use of printed compositions is very advantageous regarding process cost and flexibility. Although several authors already reported micro-structures based on organic sacrificial layers, such as the combination of SU-8 (over-layer) and polypropylene carbonate (sacrificial material) [1], the required processing temperatures remain too high for most polymer applications. In this work, we introduce materials with significantly lower sacrificial layer decomposition temperatures, thereby considerably extending the application field of this process. The key here is naturally the formulation of the sacrificial pastes. It must be stable at the overlayer processing temperature, yet decompose / evaporate cleanly at a temperature low enough to avoid degradation of the polymer. Also, the sacrificial materials must have a low toxicity, and ideally degrade in the solid state to avoid collapse of fine structures by capillary effects. The selected sacrificial material consists of heat-degradable polymers or sublimable polyol-type compounds, formulated as thick-film pastes. Studies were therefore performed with several solvents to determine the most suitable formulation to obtain the correct rheology for screen-printing (ca. honey-like consistency). In this work, we use various epoxy resins and silicones as thermosetting polymers, optionally filled with graphite to impart electrical conductivity and improve mechanical stability. Formulation of this over-layer should also require careful attention. A too strong interaction between the sacrificial paste and the top layer could result in potential destruction of the sacrificial material. Based on the investigated structuration methods, the operation of several devices, such as simple fluidic circuits (Fig 2) or micro-mechanical bridges / cantilevers, is demonstrated.

2010

Fabrication of Polymer-Based Micro Devices: Formulation and Study of the Paste

Olivier Gentsch, Thomas Maeder, Peter Ryser, Nathalie Sophie Adeline Serra

We investigate in the present work the fabrication of polymer-based micro-fluidic and micro-mechanical devices using sacrificial, resistive/conductive pastes, through a screen-printing process. An organic sacrificial paste is first screen-printed onto a substrate, the future opening in the structure existing where the paste lies (channels, cavities...). Then, a resistive paste based on thermosetting polymer resin and graphite is deposited onto the previous layer. Finally, the sacrificial paste is removed at 150°C by sublimation through the composite, leaving therefore the desired pattern. For such applications, the key is naturally the formulation of the pastes. On a previous work, we already proposed a potential formulation for the organic sacrificial paste, based on polyols [1]. In the present paper, we will focus on the formulation of the cover paste, which must be adapted rheologically for the screen-printing process, but also chemically due to strong potential interactions between the sacrificial layer and the over-layer. Finally, micro-devices such as simple fluidic channels and suspended structures were produced and shown to be operational, demonstrating the high potential of our process.

Elsevier2011

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We investigate in the present work the fabrication of polymer-based micro-fluidic and micro-mechanical devices using sacrificial, resistive/conductive pastes, through a screen-printing process. An organic sacrificial paste is first screen-printed onto a substrate, the future opening in the structure existing where the paste lies (channels, cavities.). Then, a resistive paste based on thermosetting polymer resin and graphite is deposited onto the previous layer. Finally, the sacrificial paste is removed at 150 C by sublimation through the composite, leaving therefore the desired pattern. For such applications, the key is naturally the formulation of the pastes. On a previous work, we already proposed a potential formulation for the organic sacrificial paste, based on polyols [1]. In the present paper, we will focus on the formulation of the cover paste, which must be adapted rheologically for the screen-printing process, but also chemically due to strong potential interactions between the sacrificial layer and the over-layer. Finally, micro-devices such as simple fluidic channels and suspended structures were produced and shown to be operational, demonstrating the high potential of our process. (C) 2010 Published by Elsevier Ltd.

Elsevier Science, Reg Sales Off, Customer Support Dept, 655 Ave Of The Americas, New York, Ny 10010 Usa2010

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2010