Modeling and control of rapid cure in polydimethylsiloxane (PDMS) for microfluidic device applications

Polydimethylsiloxane (PDMS) is an important thermosetting elastomer for microfluidic devices because it can replicate nano-scale features and form flexible membranes useful for microactuation. PDMS is used extensively in research environments because it is readily available and biocompatible. However, the prototyping process is too slow for volume manufacturing. The dominant rate limiting step is curing, and high temperature cures used to speed the curing process have adverse effects on the shape of the parts produced. This thesis examines the PDMS cure process and presents a methodology to intelligently design faster cure processes without compromising the quality of parts produced. The first part of this thesis applies statistical mechanics to relate the time evolution of cure with the modulus of elasticity. This enables mechanical testing strategies to be used in situ to monitor the extent of cure, which is important to determine the critical gel point and quantify when the cure process is complete. The gel point describes when PDMS first transitions from a liquid to a solid, and is important for modeling shrinkage and warpage. A novel heated microindentation setup is designed to monitor curing of thin PDMS films, and experimentally validate the theory. The second part of this thesis presents a model for final PDMS shrinkage and warpage using the gel point. Gelation is spatially and temporally distributed, and temperature at the gel point has a direct impact on the shrinkage and warpage observed. The model is validated with experimental data. Since gel temperature is the only parameter to affect shrinkage and curvature, the cure process is accelerated after the gel point without affecting dimensional quality. Increasing the process temperature immediately following gelation is indeed shown to decrease the current cure process time by a factor of five, while maintaining comparable quality. Tolerances on shrinkage and curvature can be used with these models to determine the gel temperatures required, and design multi-temperature processes that speed the cure process.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Wong, Eehern J

Advisor dc:contributor.advisor

• Jung-Hoon Chun.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/61615

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/61615