Fabrication, Characterization, Modeling, and Performance of Thin Nanoporous Membranes.

摘要

Nanoporous devices are up-and-coming platforms for selective molecule separation and sensing. They have great potential for high throughput and economy in manufacturing and operation. Acting as mass transfer diodes similar, tapered pores are proven to have superior performance characteristics compared to traditional cylindrical pores. Nevertheless, such phenomena remain to be exploited for molecular separation. In this thesis, we present fabrication, characterization, modeling, and performance results of thin silicon based sieves created by interferometric lithography, an approach which is ideally suited for the integration of nano-structured materials into microfluidic processing systems. Millimeter sized planar arrays of uniformly cylindrical and pyramidal nanopores are created in silicon nitride and silicon respectively with pore diameter/side length 200 nm or smaller.;Molecular transport properties of the fabricated devices are investigated by molecular dynamics simulations against state-of-the-art polycarbonate track etched (PCTE) membranes. Higher diffusion rates are achieved with thin pores among which the highest rates were for thin cylindrical pores. The best separation capability, on the other hand, is achieved with pyramidal pores in presence of electrostatics. Increasing the pore size and decreasing the molecule size increased the rates and fluxes and decreased the pore clogging probability in general. The least possibility of fouling is achieved with pyramidal pores having molecular transport from small to large square. For the pore/protein ratio .10, highly restricted motion is demonstrated with cylindrical pores.;Transport properties of short cylindrical pores are also compared against PCTE membranes, experimentally. Diffusion and separation of two similar sized proteins, bovine serum albumin and bovine hemoglobin, are studied. 50 fold higher pore fluxes are achieved with thin silicon nitride membranes relative to commercial sieves, without any modification of the membrane surface. At pH 4.7, 4.99 and 0.96 BSA selectivities are achieved with thin and thick sieves, respectively. BHb selectivities at pH 7.0, on the other hand, were 1.92 and 1.51 with nitride and commercial PCTE membranes, respectively. We show that the simulation results are in agreement with experimental results, and molecular dynamics simulations are suitable to understand the separation processes.