Emanuel Waddell*, Timothy J. Johnson, David J. Ross**, David L. Pugmire**, Michael J. Tarlov**, Gary W. Kramer*, and Laurie E. Locascio**

*Analytical Chemistry Division, **Process Measurements Division
 

We have successfully fabricated and characterized microchannels in polymer substrates using laser ablation.  Additionally, we have demonstrated that it is possible to change the chemical functionality and surface charge in these microchannels by performing the laser ablation under different local chemical environments.  This technique allows one to spatially confine changes in the surface chemistry of the polymer.  Consequently, it is possible to tailor the electroosmotic mobility and chemical functionality to specific process needs.  Laser-ablated microchannels were fabricated using a KrF laser (248 nm) and a computer-controlled positioning stage.  In this work, we examined the physical, chemical, and electroosmotic flow characteristics of the microchannels formed in copolyester, polystyrene, polycarbonate, and poly (methylmethacrylate) ablated under chemical environments such as nitrogen, oxygen, water, and methanol.  For example, ablation under methanol results in reduced surface charge as compared to ablation under oxygen or nitrogen.  This change in surface charge is evidenced by a chemical mapping technique in which group-specific fluorescent probes are used to characterize polymer surfaces.  In addition to the use of fluorescent mapping, x-ray photoelectron spectroscopy (XPS) was utilized to image the surface.  Results from electroosmotic mobility measurements also provide evidence of a modified surface charge.  In this instance, channels ablated under methanol had a lower electroosmotic flow than those ablated under nitrogen or oxygen.  This presentation will compare the differences observed in laser ablated polymers as characterized by optical profilometry, electroosmotic flow measurements, XPS, and chemical mapping.