Dry adhesive bonding of nanoporous inorganic membranes to microfluidic devices using the OSTE(+) dual-cure polymer
We present two transfer bonding schemes for incorporating fragile nanoporous inorganic membranes into microdevices. Such membranes are finding increasing use in microfluidics, due to their precisely controllable nanostructure. Both schemes rely on a novel dual-cure dry adhesive bonding method, enabled by a new polymer formulation: OSTE(+), which can form bonds at room temperature. OSTE(+) is a novel dual-cure ternary monomer system containing epoxy. After the first cure, the OSTE(+) is soft and suitable for bonding, while during the second cure it stiffens and obtains a Young's modulus of 1.2 GPa. The ability of the epoxy to react with almost any dry surface provides a very versatile fabrication method. We demonstrate the transfer bonding of porous silicon and porous alumina membranes to polymeric microfluidic chips molded into OSTE(+), and of porous alumina membranes to microstructured silicon wafers, by using the OSTE(+) as a thin bonding layer. We discuss the OSTE(+) dual-cure mechanism, describe the device fabrication and evaluate the bond strength and membrane flow properties after bonding. The membranes bonded to OSTE(+) chips delaminate at 520 kPa, and the membranes bonded to silicon delaminate at 750 kPa, well above typical maximum pressures applied to microfluidic circuits. Furthermore, no change in the membrane flow resistance was observed after bonding.