Surface characterization of laser-ablated polymers used for microfluidics

Fabrication of microfluidic devices by excimer laser ablation under different atmospheres may provide variations in polymer microchannel surface characteristics. The surface chemistry and electroosmotic (EO) mobility of polymer microchannels laser ablated under different atmospheres were studied by X-ray photoelectron spectroscopy and current monitoring mobility measurements, respectively. The ablated surfaces of PMMA were very similar to the native material, regardless of ablation atmospheres due to the negligible absorption of 248-nm light by that polymer. The substrates studied that exhibit nonnegligible absorption at this energy, namely, poly(ethylene terephthalate glycol), poly(vinyl chloride), and poly(carbonate), showed significant changes in surface chemistry and EO mobility when the ablation atmospheres were varied. Ablation of these three polymer substrates under nitrogen or argon resulted in low EO mobilities with a loss of the well-defined chemical structures of the native surfaces, while ablation under oxygen yielded surfaces that retained native chemical structures and supported higher EO mobilities.