A modified quasi-creep model for assessment of deformation of topas COC substrates in the thermal bonding of microfluidic devices : Experiments and modeling

The effects of thermomechanical properties of dissimilar polymer plates on thermal bonding were investigated and the resultant deformation of cover Topas COC plate was modeled using a simplified quasi-creep model. The appropriate conditions for thermal bonding for minimal deformation of both the Topas cover and substrate plates could be established through simulation using the quasi-creep model. Both the cover plate and the substrate containing microchannels were fabricated by injection molding. The elastic modulus of the COC plate at different temperatures was measured using three-point bending test. The thermal bonding was conducted at different temperatures, pressures, and holding times. The deformation of the cover plate (consisting of Topas with a lower glass transition temperature, T_g) into the microchannel of the substrate plate (consisting of Topas with a higher T_g) was found to be significant even at lower bonding pressures when the bonding temperature was higher than a critical temperature. Such deformation was dependent on the viscoelastic creep behavior of the material and the thermal bonding temperature and load. This deformation behavior was predicted by the numerical model, and the predicted results agree well with the experimental data. The bonding strength of the sealed microchannels was evaluated using the burst test. © 2011 Wiley Periodicals, Inc.