Thermal bonding of thermoplastic microfluidic devices

• Main Author: Nor Aza Hussain
• Other Authors: Tor Shu Beng
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/60959
• Institution: Nanyang Technological University

The field of microfluidics has become one of the most dynamic field in recent years. It has potential benefits of reduced size, improved performance, disposability, low cost, and reduced power consumption. Polymer materials like PMMA – (Poly (Methyl Methacrylate)), has become one of the most promising materials for microfluidics devices due to the advantages of low cost, ease of fabrication, biocompatibility and higher flexibility over glass and silicon. PMMA substrates are made commonly via micro-injection molding. There are various ways of bonding the PMMA substrate with a cover plate of the same material. In this project, thermal bonding was studied. Thermal bonding provides one of the easiest methods to bond 2 surfaces together. The effect of oxygen plasma surface treatment was also investigated and contact angles measurements were carried out to characterize the surfaces fabricated before bonding. During injection molding, residual stress are built up on the surface of the PMMA substrate which has a significant impact on the deformations formed after thermal bonding. To examine these changes, PMMA substrates of various cooling times (25s, 50s, 75s, 100s, and 125s) were molded, surface treated with Oxygen plasma, and then bonded thermally to produce the microfluidic devices before comparing their depth and width deformations with their respective untreated bonded PMMA specimens. PMMA specimen of cooling time 125s has showed the best result. It has the least amount of depth deformation (13.2%) formed after thermal bonding. The deformation gets better with increased cooling times regardless of plasma treatment. And it was also found that microchannels that are 90º to the molten injection flow are likely to deform more than those in the same direction. Lastly, the function of the bonded PMMA microfluidic devices was demonstrated through a droplet generation test. Untreated PMMA specimens are highly successful in droplet forming (water-in-oil) in the microchannels than their treated counterparts due to hydrophobicity. A method is proposed to bake the treated counterparts in an oven to regain its hydrophobic nature before the droplet test.