Improved characterization technique for micromixers

This paper reports an improved technique to characterize a micromixer. Due to the small dimensions of micromixers, the mixing relies on diffusion only. To date most diffusive micromixers have been tested with phenolphthalein and a base. However, this method does not give any information about the proportional mixing of the device, as the final colour of the mixing depends only on the pH value. For a pH below the critical point, the mixed fluid is colourless, whereas an intensive but almost constant colour is obtained at pH values above. In order to avoid any chemical reactions, the new characterization technique is based on commercially available inks of different colours. For mixing, the colours of the inks change gradually rather than at one specific point. The technique has been successfully employed to characterize a micromixer at various pressure differences. Finally, image processing was used to allow observation of proportional mixing and to characterize the development of the diffusion over time. The latter feature could be an interesting technique to monitor the course of a reaction over the length of the mixer (stopped flow technique).