Demolding of hot embossed polymer microstructures

Polymer-based microfluidic "lab on a chip" technology promises to reduce cost and extend access to medical diagnostic tests that formerly required expensive and labor-intensive lab work. The predominant methods for manufacturing these devices are miniaturized molding processes including casting, injection molding, and hot embossing. These techniques have in common the use of a mold to define the shape of functional features (fluidic channels), the separation of the part from the mold as a process step (demolding), and the intended re-use of the mold to produce additional parts. The demolding step in particular poses significant challenges for mass production. Demolding affects several issues including production rate, part quality, and mold lifetime, and demolding-related defects are frequently observed. Despite its importance, there has been no comprehensive effort to analyze demolding theoretically or experimentally. This thesis aims to deepen the understanding of demolding of polymer microstructures in order to facilitate mass manufacturing of polymer-based devices with micro-scale functional features, such as microfluidic chips. A theory of demolding mechanics has been proposed that combines the effects of thermal stress, friction, and adhesion in a unified framework. A metric by which demolding can be characterized experimentally--the demolding work--has been proposed by analogy with interfacial fracture and has been related to underlying physical mechanisms. Finite element simulations based on this theory of demolding have been performed to investigate the effects of important parameters, including demolding temperature and feature geometry. A test method for characterizing demolding by directly measuring the demolding work for individual microstructures has been developed and applied to hot embossing to study the effects of process parameters such as demolding temperature, the effects of feature geometry and layout, and the impacts of mitigation strategies such as low-adhesion mold coatings. The results of these demolding experiments broadly agree with expected trends based on the theory of demolding mechanics proposed herein. A dimensionless parameter aggregating the effects of feature geometry and layout has been identified and related to the occurrence of demolding-related defects, the demolding process window, and the demolding temperature that minimizes the demolding work. These findings have been generalized to provide processing and design guidance for industrial application of polymer micro-molding.

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

• Dirckx, Matthew E

Advisor dc:contributor.advisor

• David E. Hardt.

• 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/1721.1/61520

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/61520