Fundamental studies towards the fabrication of electroactive monolithic stationary phases in microfluidic channels

The long term goal of this project is to develop a monolithic stationary phase which utilises an electroactive polymer combining the advantages of EMLC, monolithic technology and microfluidic separation, thus creating an electroactive monolithic microchip (EMμ). In this thesis, fundamental studies towards the fabrication of EMμ are presented, i.e. integration of an electrochemical cell into a microfluidic chip, colloidal crystallization in microfluidic channels and PANI growth through a colloidal crystal template. Polyaniline was selected as the electroactive material for the fabrication of the monolithic stationary phase as its use for EMLC had already been demonstrated. Colloidal crystals have been used to microstructure materials and the inverse opal structure comprises pore sizes of the order of what was needed for EMμ; therefore electropolymerization of aniline through a polystyrene colloidal crystal template strategy was chosen. Two alternative chip designs, CD1 and CD2, were investigated for this thesis. Their applicability for EMμ was assessed in terms of their flow velocity profile using computational fluid dynamic, colloidal crystallization feasibility and electrochemical behavior using ferricyanide electrochemistry. The integration of a fully operational three-electrode electrochemical cell within a microfluidic channel and its use for polyaniline electropolymerization was demonstrated, and self-assembly of the sacrificial polystyrene template in these channels was shown. Polyaniline microstructure morphology exhibited a dependence on the surfactant concentration present in the polystyrene suspension. Finally, electrochemical switching of conducting polymer within microfluidic channels was assessed by studying polypyrrole switching by atomic force microscopy (AFM). Pore swelling and contraction was observed on application of a potential, demonstrating that the monolith properties could be dynamically controlled. It was found that volume increase in the polymer could be responsible for a deformation of flow through pores due to physical confinement of the polymer