| A complete polymeric microfluidic reactor with 500μm depth was fabricated by optimization of SU-8 2075 photolithography parameters such as spin coating, soft baking, exposure, post exposure baking, and development. A new photolithography technology was developed. According to curing shrinkage rate of SU-8 2050, a fixed amount of SU-8 2050 was taken out and spread around to the edge of PMMA substrate by a Teflon scraper. A microfluidic reactor with fixed channel depth was fabricated through soft baking, exposure, post exposure baking, and development without spin coating. Then a piece of hydroxylated BOPP film, on which SE-1 was coated, was used to seal the microfluidic structure. There was no blockage in the microchannel and the top transparency which was very useful and critical for photoreaction was significantly improved.Gold nanoparticles were synthesised in the complete polymeric microfluidic reactor under UV irradiation. The gold nanoparticle dispersions prepared by photoreaction of sodium citrate with chloroauric acid in aqueous solution were characterised by UV-vis adsorption spectrum, laser particle size analyzer and transmission electron microscope (TEM). The effects of process factors, such as flow rates of reactants, [sodium citrate]/[HAuCl4] and UV light intensity, on UV-vis adsorption intensity and diameters of gold nanoparticles were investigated. The results showed that the UV-vis absorption intensity of gold nanoparticles increased as flow rates increased, but decreased as [sodium citrate]/[HAuCl4] increased and UV light intensity increased. The diameter of gold nanoparticles decreased as flow rates increased and UV light intensity increased. At low [sodium citrate]/[HAuCl4] (<16), with its increasement the size of nanoparticles changed a little. However, at higher [sodium citrate]/[HAuCl4] (>16), the diameters of the obtained gold nanoparticles increased with the increasement of [sodium citrate]/ [HAuCl4].
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