Inner-wall modification of a commercial polymeric microfluidic chip using pulsed He/O_2 and Ar/O_2 μplasmas

摘要

Pulsed He/O-2 and Ar/O-2 miasmas were used to modify the postbonded microchannels of a commercial cyclic olefin copolymer microfluidic chip. The mu plasmas were generated throughout a 60-mm-long microchannel with a cross section of 340 x 86 mu m(2) at atmospheric pressure using Pt wire electrodes under discharge conditions of spark voltages of 8-8 kV and a pulse repetition frequency of 50 Hz with a duty ratio of 0.2%. From optical emission spectroscopy results, the electronic excitation temperature was estimated to be approximately 2.1 x 10(4)K for both He and Ar mu plasmas, and atomic oxygen radicals were increasingly produced with increasing O-2 gas concentration. The plasma-treated microchannel inner wall was analyzed by X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The wettability of the microchannel inner walls treated with both He/O-2 and Ar/O-2 shows the following tendencies; the wettability increased by about 4 times that of a raw microchannel at O-2 gas concentrations of 5-10% and then the wettability decreased with increasing O-2 gas concentration over 10%. It is found that the wetting property of the microchannels depends on both the oxygen polar groups, such as -C-O-, C=O, and COOK introduced onto the inner walls and the surface roughness due to plasma etching. (C) 2018 The Japan Society of Applied Physics