A microfluidic nanoliter mixer with optimized grooved structures driven by capillary pumping

• Published in: Journal of micromechanics and microengineering 2006-07, Vol.16 (7), p.1358-1365
• Main Authors: Chen, C F, Kung, C F, Chen, H C, Chu, C C, Chang, C C, Tseng, F G
• Format: Article
• Language: English
• Subjects: Applied fluid mechanics; Applied sciences; Exact sciences and technology; Fluid dynamics; Fluidics; Fundamental areas of phenomenology (including applications); Mechanical engineering. Machine design; Physics; Precision engineering, watch making
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/16/7/033

It is known that surface tension-capillary pumping is an effective driving force in a microchannel, however a power-free mixer that uses only surface tension has not yet been achieved. In the present study, a power-free method is explored to perform mixing in a microchannel without any external active mechanisms such as pumps, valves or external energies like electrostatic or magnetic fields. The mixer is cost effective as the channel is designed to have no sidewalls with the liquid being confined to flow between a bottom hydrophilic stripe and a top-covered hydrophobic substrate. It is found from both theoretical analysis and experiments that for a given channel width, the flow rate solely due to capillary pumping can be maximized at an optimal channel height. The flow rate is in the order of nanoliters per second, for example, the flow rate is 0.65 nL s-1 at the optimal channel height 13 mum, given the channel width 100 mum. It is most crucial to this power-free mixing device that two liquid species must be well mixed before the liquids are transported to exit to a reservoir. For this purpose, asymmetric staggered grooved cavities are optimally arranged on the bottom substrate of the channel to help mixing two different liquid species. It is shown that maximum mixing occurs when the depth of the grooved structures is about two-thirds of the total channel height.