Solvent-based bonding of PMMA-PMMA for microfluidic applications

Solvent bonding is a simple, inexpensive and quick technique used for joining microfluidic parts made of thermoplastic polymers that results in high bonding strength and good optical clarity. However, selecting the right solvent as well as the curing conditions is an important step in providing a successful bond that ensures an appropriate bonding without squeeze-out and clogging of microchannels. In this study, different solvent mixtures and solvent phases (i.e., liquid vs. vapor), as well as a range of curing times and temperatures, were tested to bond poly(methyl methacrylate) samples. Additionally, effect of corona surface modification was also examined on bonding quality. Results were compared in terms of bonding strength and optical clarity. A solvent mixture of 20% dichloromethane and 80% isopropanol showed the greatest bonding strength (4.2 MPa, based on tensile test), while vaporized dichloromethane had the best optical clarity (only 2.22% reduction in power transmittance). Coronal surface modification also showed a 25% increase in bonding strength and 2% improvement on optical clarity, for 20% dichloromethane and 80% isopropanol solution at room temperature and curing time of 15 min.