We have combined self-assembled ceramic nanoislands with nanoimprinting to demonstrate a novel, simple, low-cost method for polymer surface patterning. The nanoislands are easy to make and inexpensive, and can produce different distinct island morphologies. With a similar stiffness to steel, the nanoislands have superior durability to silicon, glass, polydimethylsiloxane (PDMS), and other common nanoimprinting materials. The nanoislands are stable up to 1000 degrees C and resist acids, bases, and solvents. We have demonstrated nanoimprinting with PDMS, ethyleneglycol dimethacrylate, and polystyrene polymers. The combination of desirable properties, ease of making, and low cost suggests a useful nanopatterning platform for a wide array of research fields.
The effects of nanoparticles and high-pressure carbon dioxide (CO 2 ) on shear viscosity of polystyrene (PS) were studied. Master curves of PS, PS þ 5 wt % carbon nanofibers (CNFs), and PS þ 5 wt % nanoclay (Southern Clay 20A) without CO 2 were created based on parallel-plate measurements. The results showed that addition of nanoparticles increased the viscosity of the neat polymer. Steady-state shear viscosity of PS in the presence of CO 2 and nanoparticles was measured by a modified Couette rheometer. The effect of supercritical CO 2 on these systems was characterized by shift factors. It was found that under the same temperature and CO 2 pressure, CO 2 reduced the viscosity less for both PS-20A and PS-CNFs than neat PS. Between the two types of nanoparticles, CNFs showed a larger viscosity reduction than 20A, indicating a higher CO 2 affinity for CNFs than 20A. However, the advantage of CNFs over 20A for larger viscosity reduction decreased with higher temperature. A gravimetric method (magnetic suspension balance) was used to measure the excess adsorption of CO 2 onto CNFs and nanoclay, thus, CO 2 showed a higher affinity for CNFs.
In this study we design new fabrication techniques and demonstrate the potential of using dense CO2 for facilitating crucial steps in the fabrication of polymeric lab-on-a-chip microdevices by embedding biomolecules at temperatures well below the polymer's glass transition temperature (T(g)). These new techniques are environmentally friendly and done without the use of a clean room. Carbon dioxide at 40 degrees C and between 4.48 and 6.89 MPa was used to immobilize the biologically active molecule, beta-galactosidase (beta-gal), on the surface of polystyrene microchannels. To our knowledge, this is the first time dense CO2 has been used to directly immobilize an enzyme in a microchannel. beta-gal activity was maintained and shown via a fluorescent reaction product, after enzyme immobilization and microchannel capping by the designed fabrication steps at 40 degrees C and pressures up to 6.89 MPa.
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