Doctor of Philosophy (PhD)
This study aims to develop a process which allows 3D integration of micro and nanostructures in microchannels. A fabrication process was established for the large area integration of hierarchical micro and nanostructures in microchannels. This novel process, which is called 3D molding, takes advantage of an intermediate thin flexible stamp such as PDMS from soft lithography and a hard mold such as brass from hot embossing process. However, the use of a thin intermediate polydimethylsiloxane (PDMS) stamp inevitably causes dimensional changes in the 3D molded channel, with respect to those in the brass mold protrusion and the intermediate PDMS stamp structures. We have investigated the deformation behavior of the 3D molded poly(methyl methacrylate) (PMMA) substrate and the intermediate PDMS stamp in 3D molding through both experimentation and numerical simulation. It was found that for high aspect ratio brass mold protrusion, the maximum strain of the intermediate layer occurs in the bottom center of the 3D channels. However, with decreasing the aspect ratio of brass mold protrusion the highest elongation occurs at the bottom corners of the channel causing less elongation of the intermediate PDMS stamp and imprinted structures on the bottom surface of the 3D channel. A modified 3D molding process which is called 3D nanomolding is developed which allows nanopatterning the surface of small microfeatures. Using 3D nanomolding process and solvent assisted bonding microdevices with no side, one side, three sides and four sides patterned were fabricated. To characterize 3D flow patterns induced by the surface structures on microdevices, confocal microscopy was used as dyed water and undyed water injected from separate inlets of micromixer were mixed along the microchannel at flow rates of 10 and 40 μL/min. The standard deviation of the normalized intensity measured in the confocal image of the cross section of the channel was used for quantifying the degree of mixing and evaluating the mixing performance of all four different microdevices. Experimental and simulation results show that by patterning the surface of the micromixer, flow patterns can be manipulated, which can improve mixing through stretching and folding of fluid elements and therefore increasing the interfacial area between fluids and cutting down the diffusion length. The effect of increasing velocity on increasing standard deviation (decreasing mixing) was also found to be less for the micromixers whose surfaces are patterned compared to the plain channel.
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Farshchian, Bahador, "3D integration of micro- and nanostructures into bio-analytical devices" (2013). LSU Doctoral Dissertations. 1241.