Mechanical and chemical analysis of plasma and ultraviolet–ozone surface treatments for thermal bonding of polymeric microfluidic devices

Abstract

Here we have demonstrated that radio frequency plasma and ultraviolet–ozone (UVO) surface modifications are effective treatments for enabling the thermal bonding of polymeric microfluidic chips at temperatures below the T_g (glass transition temperature) of the polymer. The effects of UVO and plasma treatments on the surface properties of a cyclic polyolefin and polystyrene were examined with X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM) surface roughness measurements and surface adhesion measurements with AFM force–distance data. Three-point bending tests using a dynamic mechanical analyzer (DMA) were used to characterize the bond strength of thermally sealed polymer parts and the cross-sections of the bonded microchannels were evaluated with scanning electron microscopy (SEM). The experimental results demonstrated that plasma and UVO surface treatments cause changes in the chemical and physical characteristics of the polymer surfaces, resulting in a decrease in T_g at the surface, and thus allowing the microfluidic chips to be effectively bonded at temperatures lower than the T_g of the bulk polymer without losing the intended channel geometry.