Effect of partial UV illumination on a mixture of water and a methylene blue solution in a microchannel coated with TiO2

Effects of UV illumination on a mixture of water and a methylene blue (MB) solution in a TiO2-coated microchannel were investigated by changing the illuminated section. The TiO2 coating possessed photocatalytic activity. The mixing length of the liquids increased during UV illumination of an entire microchannel. However, the length became around 20% shorter than that before UV illumination when the UV illumination section was limited at the straight portion of the microchannel. The braking effect of liquid flow at the UV–dark border probably plays an important role in this phenomenon.