Hydrophilicity modification of poly(methyl methacrylate) by excimer laser ablation and irradiation

Because of the micromachining characteristic of excimer laser ablation, the microchannels ablated with this technique on poly(methyl methacrylate) (PMMA) substrate have definite surface roughness. Utilizing this characteristic, the hydrophilicity of PMMA microchannels could be directly modified during fabrication process both by the mechanism of photochemical ablation and the effect of surface roughness. The contact angle is inversely proportional to the surface roughness under ablation with same fluence and could be reduced to 25 degrees by choosing ablation parameters reasonably (7.38 J/cm(2), 20 Hz, 10 mm/min). Excimer laser irradiation of PMMA substrates for different irradiation times at fluence below the ablation threshold also results in the surfaces becoming more hydrophilic without any marked change in the surface topography. The contact angle decreases with the increase of irradiation times and finally reaches the saturated status after irradiation for 2,500 times. Under same irradiation times, higher fluence led to PMMA substrates more hydrophilic.