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ABSTRACT: The advantage of using electrowetting as a novel principle for a reflective display has been previously demonstrated. The principle is based on the controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator. The main objective of this paper is to show experimentally the influence of surfactants on the electro-optic behavior of a single electrowetting pixel. The concentration and type of nonionic surfactant (Tween 80 and Span 20) have been varied. The experimental data are compared with calculations from the electro-optic model developed previously. The electro-optic performance is significantly affected by the nature and the concentration of surfactant. In the presence of Tween, at concentrations lower than the critical micelle concentration (CMC), and mixtures of Tween and Span the electro-optic behavior can be related to the interfacial tension. When decreasing the oil/water interfacial tension, the amplitude of the driving voltage required for obtaining a given oil displacement decreases and the switching curve becomes steeper. These effects can be accurately reproduced by means of the previously developed electro-optic model. Mixtures of Tween and Span produce a significant synergetic reduction of the driving voltage. For Tween concentrations higher than the CMC and Span, a strong disagreement is observed between the previously developed model and experimental data. Here a new physical model is reported that describes the electro-optic behavior of electrowetting-based optical elements in the presence of surfactants. The model takes into account the actual voltage used to control the liquid movement in electrowetting (lower than the applied voltage), the amount of surfactant adsorbed at the decane/water interface, and the dipole moment of the surfactant molecules. The calculated results are in very good agreement with experimental data without employing fitting parameters. The dipoles interact with the applied field and lower the actual applied field. This reduction of the effective electric field across the solid-liquid interface induces a decrease in the charge density at the solid-liquid interface and reduces the electrowetting force. For surfactant concentrations higher than the CMC, the electro-optic performance does not depend on the surfactant concentration. This demonstrates that the reduction of the electrowetting field due to the large dipole moment of the surfactant molecules occurs at the oil/water interface. A new method for the test cell fabrication is also presented.
Langmuir 09/2009; 25(21):12771-9. · 4.19 Impact Factor
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ABSTRACT: Photocatalysis is often used in air purification. Photocatalytic degradation od VOC's has been investigated in a number of devices. An optimisation of this process requires a chracterisation of the reactor : in a first step the gas flow behaviour has to be studied (plug flow, CSTR,...) by RTD analysis; then, chemical kinetics have to be determined as a function ot the relevant parameters (space time, relative humidity, concentrations, etc). All the data collected lead to a reliable design of the equipment.
05/2009;
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ABSTRACT: Vitamin A is used as a generic term for all vitamin A derivatives with retinol-like biological activity. Retinol is the main parent compound for vitamin A. It derives from carotenoids (provitamin A) and also directly from the pre-formed vitamin A contained in the diet. The term "retinoid" is a generic descriptor of compounds structurally related to vitamin A and the synthetic analogues of retinol with or without biological activity. Retinoic acid is the active cellular catabolite. Vitamin A/retinoids have been given cancer-preventive functions and subsequently used in clinical trials to reduce lung cancer incidence in high-risk individuals. The results obtained have been in contradiction with both in vivo and in vitro promising studies. It seems therefore necessary to develop a better understanding of the vitamin A/retinoids signalling pathways in the lung. With this aim, we summarise the relevant knowledge focussed on the lung.
Lung cancer (Amsterdam, Netherlands) 05/2009; 66(1):1-7. · 3.14 Impact Factor
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ABSTRACT: Photocatalytic micro-channel reactor was built by using stereolithography process. A reactor with a micro-channel as a support of TiO2 photocatalyst was designed in order to reduce dimensions while improving the efficiency. Photocatalytic activity of the micro-reactor at various flow rates was evaluated by the inlet and outlet concentrations of salicylic acid as a model of pollutant. Influence of the initial pollutant concentration, the irradiation intensity on the rate of degradation of the pollutant was studied. A model with the kinetic parameters for the given support geometry was applied to reactor design and scale-up.
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ABSTRACT: This paper illustrates the electrowetting behavior of aqueous dispersions of quantum dots (QDs) functionalized with 3-mercaptopropionic acid. The pH, QD concentration, type of QDs (core/shell CdSe/CdS versus CdTe/CdS) and the polarity of the voltage have been varied. The major parameter that controls the electrowetting properties is the polarity of the applied potential. This is explained by the electrophoretic transport of the negatively charged QDs to the in-liquid electrode (air/water interface) or to the fluoropolymer surface depending on the polarity of the electric field. In the negative range of applied voltage, the reversibility is excellent and contact angle hysteresis is minimal (1–2). The electric field favors the accumulation of the QDs at the air/water interface which reduces the liquid/vapor surface tension. The contact angle values depend mainly on the QD concentration regardless of pH and QD composition. For positive applied voltages, the electrowetting behavior becomes different. The adsorption of the QDs onto the fluoropolymer surface is observed when the electric field is applied. The adsorption increases with both the pH (negative zeta potential of the QDs) and the QD concentration. The surface roughness in the presence of adsorbed QDs leads to non-reversible electrowetting and significant contact angle hysteresis. The large contact angle change versus voltage at basic pH and high QD concentration is attributed to the enhancement of the capacitance of the fluoropolymer dielectric layer due to the presence of highly insulating QDs adsorbed onto the fluoropolymer surface.Graphical abstractThe electrowetting behavior of aqueous dispersions of quantum dots (QDs) has been investigated by varying the pH, QD concentration, QD composition (core/shell CdSe/CdS versus CdTe/CdS) and the polarity of the applied voltage.Research highlights► Electrowetting properties are affected by the polarity of the applied potential. ► Negative voltage: highly reversible electrowetting with very low hysteresis. ► Negative voltage: contact angle values depend mainly on the QD concentration. ► Positive voltage: non-reversible electrowetting and large contact angle hysteresis. ► Positive voltage: large contact angle change at basic pH and high QD concentration.
Colloids and Surfaces A Physicochemical and Engineering Aspects 377:269-277. · 2.24 Impact Factor
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ABSTRACT: Photocatalysis is often used in air purification. Photocatalytic degradation od VOC's has been investigated in a number of devices. An optimisation of this process requires a chracterisation of the reactor : in a first step the gas flow behaviour has to be studied ( plug flow, CSTR,...) by RTD analysis; then, chemical kinetics have to be determined as a function ot the relevant parameters (space time, relative humidity, concentrations, etc). All the data collected lead to a reliable design of the equipment.
