EP41S-5 is a two-part epoxy system that can be used for bonding, sealing, and coating a wide variety of materials. It can adhere to a variety of surfaces and is chemically-resistant, particularly towards organic solvents (e.g., methylene chloride and acetone) and strong acids (e.g., hydrochloric acid and nitric acid). This makes it a good choice for bonding different materials together when solvents or strong acids will be used in the final application. Although it can be cured at either room temperature within 3–5 days, in order to optimize its chemical resistance it is critical to add heat at higher temperatures such as 150–200°F for a few hours. These properties make it suitable for bonding fittings to substrates, such as in microfluidic devices.1
Microfluidic chips can be used to form uniform micro- and nanoparticles, particularly those used in drug delivery applications, but they suffer from low particle production rates. Researchers at the University of Pennsylvania have developed an all-silicon/glass microfluidic particle generator to overcome the trade-off between the number of integrated droplet generators and the maximum throughput of each generator. EP41S-5 was used to bond steel compression fittings to a glass wafer to construct the device, and then chemically etched PTFE tubing was connected to the fittings.
Key Parameters and Requirements
For the microfluidic device to operate over a wide range of temperatures and solvents, it was necessary to ensure that all components were solvent and heat-resistant. EP41S-5 was used as a chemically-resistant adhesive to bond stainless steel compressed fittings to a glass wafer to feed liquid materials into the microfluidic device. The epoxy-based EP41S-5 was simply cured at room temperature for 4 days.
The authors designed a microfluidic reactor that generated monodisperse (coefficient of variation < 3%) PCL microparticles dispersed in methylene chloride more than 10,000× faster than previous approaches. The channels could operate at a maximum pressure exceeding 1000 psi and high temperatures. All components of the device were chemically resistant, allowing it to generate particles in a medium containing dichloromethane. Chemically-resistant EP41S-5 was chosen to connect steel compression fittings to the glass wafer of the device. After curing, PTFE tubing was connected to the steel fittings at the inlet and outlet. The authors produced two gallons of the methylene chloride-nanoparticle emulsion within 75 minutes without any device failure.
These results show that due to its chemical resistance, EP41S-5 ensured that dichloromethane and other liquids flowing through the device did not leak and damage the connections between device components, ensuring its continuous operation.
1Yadavali, S.; Jeong, H. H.; Lee, D.; Issadore, D. Silicon and Glass Very Large Scale Microfluidic Droplet Integration for Terascale Generation of Polymer Microparticles. Nat. Commun. 2018 91 2018, 9 (1), 1–9. https://doi.org/10.1038/s41467-018-03515-2.