Projects per year
In this thesis an all polymer micropump, and the fabrication method required to fabricate this, are examined. Polymer microfluidic. devices are of major scientific interest because they can combine complicated chemical and biological analys~s in cheap and disposable devices. The electrode system in the micropump is based on the conducting polymer poly(3,4 ethylenedioxythiophene) (PEDOT). The majority of the work conducted was therefore aimed at developing methods for patterning and processing PEDOT. First a method was developed, where the conducting polymer PEDOT can be integrated into non-conductive substrates like polymethylmethacrylate (PMMA), polystyrene (PS), and cyclic olefin copolymer (COC). The integration is done after the polymerisation, in a washing step where the residual salt from the polymerisation is removed. By using a washing solvent that both removes the salt and dissolves the top layer of the substrate, the PEDOT is integrated into the non-conductive polymer. The result is a material that retains the good conductivity of PEDOT, but gains the mechanical stability of the substrate. The best results were obtained for PEDOTjPMMA. The new mechanically stable PEDOTjPMMA was micro-patterned using clean room techniques. The conductive blend was coated with a layer of photoresist, exposed and developed. The resulting pattern was etched in a reactive ion etcher, yielding a well defined patterned with a resolution of approximately 2 J..lm. This technique was utilised to fabricate an ac electroosmotic (ACEO) micropump. The ACEO pump consists of an array of interdigitated small and large PEDOTjPMMA encapsulated in a polyurethane (PUR) channel system. The pumping velocity was detected using fluorescent microspheres and a confocal microscope. The pump characteristics resembled those of pumps based on metal electrodes as reported in literature. There was, however, an indication that the PEDOT electrodes were easier damaged than metal electrodes, but the damage could be prevented by applying a thin layer of protective non-conductive polymer on top of the electrodes. A new stretchable conductive polymer was developed by mixing polyurethane in to the solution from which the PEDOT was cast. The resulting PEDOTjPUR material showed good conductivity. The film was elongated 50 % ten times and apart from a small irreversible increase in resistance during the first elongation, the film resistance was; stable during the rest of the elongations. Another set of films was stretched 200% four times. At approximately 100 % elongation, a significant decrease in conductivity was observed, but the films still remained fairly conductive during the following elongations. The aging of the films was examined at 21°C and 60°C and a logarithmic decay in conductivity with time was observed at both temperatures. The expected lifetime was found to be several years if stored at room temperature. Next, a new method for patterning conducting polymers is described. A photoresist master, with a bas-relief pattern, is fabricated using classical clean room techniques. On top of the master a hot agarose solution is cast. When cooled the agarose solidifies and forms a high water content gel with good mechanical stability. The cooled agarose stamp, with the inverse bas-relief pattern, is peeled off the master and impregnated with a deactivation agent. When placed on a conducting polymer film the deactivation agent diffuses from the stamp to the conducting polymer in the areas of contact, hence the film is deactivated in a pattern spatially defined by the relief pattern of the stamp. A resolution of approximately 2J-tm was. achieved. Finally, the PEDOT/PUR material was patterned using an inkjet printer. The inkjet printing was done on a scientific inkjet printer, where the nozzles can be observed by a _video camera and the drop expelling force and frequency can be controlled. To achieve proper printing it was required to synthesise a new short chained polyurethane. The resolution of the inkjet printer was in the order of 200 J-tm. The inkjet printed pattern is compared with the agarose stamping technique in a setup where the conductivity perpendicular to the stretching direction is measured on two electrodes fabricated by the two methods.
|Number of pages||107|
|Publication status||Published - Mar 2008|