The wettability of a surface has been shown, for many years now, to increase by the application of a voltage difference between the liquid droplet and the substrate, 1À3 which, most often, is a conductor covered by a dielectric (electrowetting on the dielectric, EWOD). There are basically two explanations of the phenomenon. The first one considers that the solidÀliquid surface tension is modulated by the electrostatic energy stored by the unit area in the effective capacitance created by the liquid and the substrate. 4 The second explanation considers that there is a net force acting on the electric charge that accumulates at the triple line (TPL) formed among the air, the solid substrate, and the liquid. 5,6 In fact, irrespectively of the explanation given, the contact angle decrease is independent of the polarity of the applied voltage, and the LippmannÀYoung 7 equation for the static contact angle change,has been experimentally demonstrated 8 for a wide range of voltage values prior to a saturation regime. In eq 1, θ 0 is the contact angle before the voltage is applied, θ V is the contact angle after a voltage V is applied, ε 0 is the vacuum permittivity, ε r and d are the relative permittivity and the thickness of the dielectric layer, respectively, and γ LV is the surface tension of the liquidÀgas interface. This increase in wettability contrasts with the decrease in wettability observed after electron bombardment. 9 In a recent paper, 10 we preliminarily discussed a contactless method to increase the wettability by creating the charging conditions of the TPL by air ionization using a corona charge instrument. We are providing in this article a more detailed discussion and systematic measurements of the observations we have made using this technique.Corona ionizers are based on the ionization of molecules of the surrounding air by the application of a sufficiently high potential between specific geometry electrodes (e.g., pin to plane) creating a large electric field gradient. 11 The control of static charge on insulating materials is a widespread use of this technique in the semiconductor industry to avoid undesired electrostatic discharge (ESD). In fact, this is the only practical way to neutralize static charge because grounding has no effect on the level of charge in insulators.In this article, we have used corona ionization to build electrostatic charge on a EWOD structure and analyze the effects this may have on the contact angle between a drop and the surface. Our preliminary experiments reported in ref 10 did show that the contact angle decreased after exposure to corona ionization, and this observation motivated the detailed study of the phenomenon that we report here. There are few works relating electrowetting to air ionization. Vallet et al. 12 attributed to air ionization the saturation phenomena of the contact angle, Blake 13 used a corona charging procedure to assist the study of contact angle change for a constant speed moving substrate, and Arifin et al. 14 investigated the effect of the e...

Electrowetting is widely used as a means to increase the wettability of droplets on a substrate covered by a dielectric. Although static or quasi-static models of the triple-line movement already exist, little research has been published on transient modeling coupled to the charge transient. This work describes a model of two differential equations coupling the charging to the movement taking into account friction. The model results are validated by comparison to published experimental results. The model focuses on applications, and hence the time to respond, the power consumption, and the energy and its breakdown into components are calculated. Moreover, the use of a generalized voltage source allows us to model successfully the results of a "corona charge" experiment as a means to increase wettability without contact between the electrode and the liquid sample. Finally, the model is extended to an ideal "charge-driven mode" electrowetting proposal resulting in better controllability of the speed and transient time between two contact angle values with applications to lab-on-a chip or displays.

Fabrication of nanochannels is drawing considerable interest due to its broad applications in nanobiotechnology (e.g. biomolecular sensing and single DNA manipulation). Nanochannels offer distinct advantages in allowing a slower translocation and multiple sensing spots along the channel, both of which improve the read-out resolution. However, implementing electrodes inside the nanochannel has rarely been demonstrated to our knowledge. The device described in this work is a Si-Glass anodically bonded Lab-on-a-Chip (LOC) device of a few millimetres in size capable of performing DNA manipulation. The LOC device structure is based on two mainstream microchannels interconnected by nanochannels. DNA, once trapped within the nanochannel, has been tracked throughout the length of the channel and the data have been recorded and analysed.

In contrast to this static change observed in contiguous Abstract-In conventional Electrowetting on Dielectric electrodes, it has also been shown that parallel electrodes (EWOD) devices a static change of the contact angle is observed produce dynamic wetting effects also driven by electric fields when a voltage is applied to the electrodes, usually correlated to [2][3]. The contact angle change is predicted by the Lipmannthe Lippmann equation. equation:In this paper we analyze the contact angle changes by using two different dielectrics of different materials and thicknesses and also comparing two different ways of creating the field c o 2(1) singularity at the contact line. Although it is known that the COS =CS 0 + 2 v contact design may induce a tangential electric field and a spontaneous front wetting, we have observed in our devices that the change in the contact line is still due to the interfacial where 00 is the contact angle without voltage applied, Ov is changing at the air-liquid interface. Several devices were the contact angle applying voltage, c0 is the permittivity of the fabricated using Teflon and PDMS coating on top of pyrex wafer vacuum, E and t are the permittivity and the thickness of the and silicon wafer previously oxidized. The results obtained using dielectric layer, V the applied voltage and YLG iS the surface these devices were compared to a conventional EWOD sample tension of the liquid-gas interface having PDMS deposited on top of metal electrodes previously laid tsion of th e li as eintc.out on top of pyrex wafer. We have compared the static contact As can be seen the change in contact angle induced by the angle change, produced using conventional voltage drive source, applied voltage is related to the value of surface tension and to with a similar measurement after charges were generated in the the energy stored per unit area in the liquid-dielectric-metal gas phase. We have observed quite different behaviour of the two capacitance approximated by a parallel plate capacitor. Such films used as coatings, for similar charge densities created, the theory has been shown to hold in various combinations of contact angle on Teflon samples changed much less than in the PDMS samples. Moreover, we have observed that the relaxation liquids dielectrics and electrodes. time in the Teflon sample was short, in range of seconds, whereas Moreover, such technique has been extensively used in in the PDMS samples the contact angle change remained for pTAS lab-on a chip devices to move drops on a moving path minutes and even, opposite sign charge was to be added to the gas by the arrangement of driving electrodes and the sequence of phase in order to totally recover the initial value. electrical signals applied on them, to perform manipulation of The paper also describes how the charge created in the gas drops (separation, merge, etc.), or to perform nano and micro phase was estimated. An experimental set-up consisting in a particle separation in microfluidic chips [4][5][6][7]. In some micro-amperimeter...

Fabrication of nanochannels is drawing considerable interest due to its broad applications in nanobiotechnology (e.g. biomolecular sensing and single DNA manipulation). Nanochannels offer distinct advantages in allowing a slower translocation and multiple sensing spots along the channel both of which improve the read-out resolution. However, implementing electrodes inside nanochannel has rarely been demonstrated to our knowledge. Therefore, we are highly motivated to do this research. The device described in this work is a Si-Glass anodically bonded Lab-on-a-Chip (LOC) device of a few millimeters in size using femtoliters in volume capable of performing DNA manipulation. The LOC structure is based on two mainstream microchannels interconnected by nanochannels. Organic samples as DNA will be released in the microfluidic mainstream and then, once confined in the nanochannels, are observed, manipulated and analyzed. We expect the general folded shape of DNA evolves to the unfolded linear shape due to the confinement in narrow channels. This shape is especially suitable for advanced manipulation and analysis.