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This paper reports on the exposure of superhydrophobic polytetrafluoroethylene (PTFE) coatings to common aqueous solutions which are used in biology, biotechnology and chemical sensor applications. Advancing contact angles as high as 173° for aqueous solutions were measured on the PTFE surface. Water drop sliding angles at 2° show a very low contact angle hysteresis. X-ray photoelectron spectroscopy measurements confirm that aqueous solutions can move or stay on the superhydrophobic surface without contamination. Owing to the chemical inertness of the polymer, these results indicate that superhydrophobic PTFE can be used in lab-on-a-chip and multi-sensor devices as well as in biological cultures, where aqueous solutions meet solid surfaces, without contaminating the interface.

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Background: In the last 40 years, scientific efforts were focused on the efficiency improvement in organic photovoltaic devices. Bleaching agents were used to absorb UV light and convert it into lower energy radiation appear as potential candidates for further improvements. The present contribution investigated the effect of adding umbelliferone to poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on its optical and electrical properties. Methods: Characterizations were performed under various umbelliferone concentrations. Fluorescence decay lifetimes were obtained using a MicroTime 200 system (PicoQuant). The UV–vis absorption spectra were obtained with a GE Healthcare Ultrospec 2100 pro Spectrometer. The electrical conductivity measurements as a function of temperature using a cryostat model ARS CS202AE-DMX-1AL. Results: The absorbance increases around 325 nm and decreases in the near infrared s the umbelliferone concentration is increased. It also decreases the absorption in the visible spectrum, concomitantly with a significant increase in the UV region. The electrical conductivity for the umbelliferone doped PEDOT:PSS films display an increase with increasing temperature, but does not follow a linear behavior with the increase of umbelliferone concentration in the films. Conclusion: It was shown that the absorbance displays a redshift in doped samples, while photoluminescence experiments demonstrated that UV light is converted to the visible spectrum more efficiently, which is a desirable feature for photovoltaic devices. Also, the electrical conductivity of PEDOT:PSS is increased for moderate umbelliferone concentrations.

The study of liquid droplets on solid surfaces is a well established research area. Static measurements include contact angle determinations which allow surface energy measurement. Dynamic measurements generally are reported on vibrating drops on mechanically or sonic driven surfaces. The general analysis of the physics of vibrating drops is complicated due to the internal degrees of freedom of the liquid and the stick or slip conditions at the liquid-solid contact line. Here we propose a simple and straightforward experimental method to measure the physical properties of droplets on highly hydrophobic surfaces. The first dynamic experiments of droplets on superhydrophobic surfaces are also reported.

Resumo A conversão fotovoltaica de energia é uma área de pesquisa muito ativa devido à necessidade de ampliar a participação das fontes de energia renováveis na matriz energética global. Os esforços de pesquisa vão desde a modelagem de dispositivos fotovoltaicos a partir de princípios físicos fundamentais ou fenomenologias, passando pelo desenvolvimento e caracterização de novos materiais e dispositivos aplicáveis na conversão fotovoltaica e indo até os estudos de impacto ambiental e aspectos econômicos. No presente trabalho, utilizando-se do modelo de sistema de dois níveis acoplado a um campo de fótons, apresentam-se os princípios físicos da conversão fotovoltaica de energia. Com isso, além de servir de rápido guia para os pesquisadores e estudantes no campo da conversão fotovoltaica, o problema spin-bóson é utilizado de forma pedagógica para servir como um exercício contextualizado de mecânica quântica e física dos semicondutores.