Clogging-Free Irreversible Bonding of Polycarbonate Membranes to Glass Microfluidic Devices

Abstract

An irreversible bonding method for bonding porous polycarbonate membranes to glass microfluidic devices is demonstrated. The membrane surfaces were modified with an ammonia solution that contained amino hydrophilic groups. Additionally, the glass substrates were terminated with hydroxyl groups after exposure to an oxygen plasma. Based on the dehydration reaction, reliable bonding between the glass and the porous membrane was achieved at 110 • C and was verified by the fluidic leakage tests for burst pressure (>500 kPa) and long-term durability (∼5 days). In particular, chemical modification by small ammonia molecules allowed bonding of the porous membranes without clogging to the pores. Therefore, this method has great potential for use in nanofluidic channels integrated with nanoporous membranes. Moreover, a simple disassembly strategy for the sandwich-structured microfluidic devices was proposed and realized for the reuse and recycling of glass substrates with microchannels in the event that the membrane morphology changes after long-term use. In the past decade, microfluidics and nanofluidics are becoming increasingly important for interdisciplinary research fields in chemistry, biology, medicine and physics.1 Various porous membranes can be integrated with microfluidics to enable advanced mass transport control for many applications, such as cell handing devices, 2 cell-based separation, 3 and organs-on-a-chip. 4 The bonding of membranes and device materials is one of the critical steps that prevents both fluid leakage and the maintenance of membrane performance. Simple "glue" approaches are popular to combine membranes to poly(dimethylsioxane) (PDMS) substrates involving epoxy adhesives or PDMS prepolymer liquids as an intermediate layer.5-7 These approaches present problems, including the partial clogging of the membrane pores, especially for nanoporous membranes. To solve this problem, 3-aminopropyltriethoxysilane (APTES) has been used for direct bonding of polymer substrates. [8][9][10] In one reported technique, porous polymer membranes were modified with APTES and were successfully bonded to oxygen plasma treated PDMS substrates. 8 Compared to organic polymer materials, fused silica glass is one of the most extensively used inorganic materials in microfluidics and nanofluidics due to its superior chemical stability, rigidity, optical transparency and its compatibility with well-established nanofabrication techniques.11 For the bonding of silicon or glass substrates, fusion bonding (∼1050• C), 12 or plasma activated bonding (200∼400is usually employed to obtain the permanent formation of covalent bonds between the two substrate surfaces. However, the bonding temperatures in the processes are much higher than the glass transition temperature (T g ) of the polymer membranes (<200 • C), leading to substantial damages to membranes and pores. To the best of our knowledge, there are few detailed reports on the bonding between inorganic substrates and organic porous membranes.Polycarbonate (PC) is one of the m...

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