Microfabrication process of passive and active Microfluidic devices.

The focus of the PhD research is fabrication and performance evaluation of microfluidic devices for liquid mixtures. Microchannels were created in different substrates, such as silicon, glass, polydimethylsiloxane (PDMS), sealed with PDMS through activation by oxygen plasma. These substrates were chosen due to various reasons: optical properties and transparency (PDMS and glass), thermal stability and inertness to chemical reactions (glass, silicon), fast prototyping and replication (PDMS). Fabrication of microfluidic devices was carried out using sequential processes of cleaning, lithography, wet etching, sealing. The fabricated prototypes were applied for studies of hydrodynamic interactions in mixtures with controlled injection of liquids by syringe pumps and inspection using optical fluorescence microscope. Experimental data were used for validation of theoretical microfluidic models. Various prototypes were fabricated operating under laminar flow conditions (Reynolds number smaller than 13), with following dimensions of the microchannels: width between 100 and 458 µm, depth between 20 and 64 µm, with different channel profiles: trapezoidal for silicon, circular segment for glass and rectangular for SU-08 / PDMS. In addition, different devices were coupled to the microfluidic system, including THz sensor and interdigitated electrode (IDE). Fabricated microfluidic reactors with embedded THz sensors and IDE were applied for micro mixing applications, in particular for control of composition of binary liquid mixtures.