Actionnement électriques de fluides dédiés aux microsystèmes

Recent advances in microfabrication, and the apparent neces-sity of miniaturizing detection and diagnostic systems has led to the emer-gence of a new research field called lab-on-chip, which are mostly workingwith fluids. Liquids actuations at the micrometer scale allow the develop-ment of many new methods based on electric field and potential. Electro-wetting has been widely used to displace and manipulate droplets on asurface, whereas electroosmosis has been used for bulk fluid movementand mixing. In this thesis, we propose the integration of these two phe-nomena in existing microsystems. First, electrowetting is used in a liquidmicrospotting system based on a cantilevers array. A difference of electricpotential between a fluid and a conducting substrate modify the energyof the liquid. Thus, the drop spreads on the surface and preferentially inexisting grooves in the depositing tool. We thus obtain an original way toload the cantilevers decreasing the dead volumes in the loading droplet.Moreover, if the potential difference is applied between the liquid andthe contacting surface, we can control the size and volume of depositeddroplet, thus allowing the patterning of highly hydrophobic substrates. Atheoretical model is proposed to describe and predict the fluid comport-ment ; Experimentations are in a very good agreement with the predictedcomportment and values. Electrowetting reveals to be the best electric ac-tuation for the manipulation of droplets and small volumes of liquids.Second, electroosmosis is used to concentrate particles on a piezoelectricmicromembrane. This actuation allows us to increase the number of par-ticles at the surface of the vibrating part therefore decreasing the responsetime of the sensor. A theoretical model is proposed to describe and unders-tand the effect of the electric field on both the bulk fluid and the objects insolution. Experimental validations are proposed with the design and fabri-cation of dedicated structures. Observed concentration of particles was 105higher that what is obtained with diffusion. The last step was to concen-trate biological particles in adequate bulk fluid. Results were difficult toobtain and we do not observed the desired comportment. Nevertheless,the experimentations show clearly the huge potential of this electric ac-tuation of fluid. Electroosmosis is therefore a real good phenomenon todecrease the response time of micrometric sensors.