Optimization of corona-triggered PDMS-PDMS bonding method

Presently, inexpensive hand-held corona system has been widely used as an alternative for PDMS-PDMS bonding, considering the fact that it is both effective and highly portable. In the present work, to optimize this corona-triggered bonding technique, different PDMS curing conditions and corona exposure time have been tested. The hydrophobic recovery of the corona treated PDMS surface was quantitatively studied by measuring the contact angle. Meanwhile, bonding strength was preliminarily evaluated through manually peeling. According to the present experimental results, layers of PDMS should be cured at 60degC for 60 minutes with the base-to-cure ratio of 10:1. Results of contact angle analysis indicate that hydrophobic recovery is generally the same between the surface of corona-treated PDMS and oxygen-plasma-treated PDMS. However, corona-treated PDMS has the unique advantage that within the first 30 minutes, sometimes even 1 h, it can still be peeled off and rebonded without obvious bonding strength degradation. This may be of significant importance in the multi-layer PDMS bonding process, which requires accurate alignment between different layers. Furthermore, bonding of PDMS chips with a minimum feature size of 2 mum has been demonstrated using the optimized corona-triggered PDMS-PDMS bonding technique. A long and narrowly shaped microfluidic chip has been sealed successfully in which no noticeable leakage was observed with a flow rate up to 1 muL/s.