Mixing in systems at the microscale and macroscale has been well characterized, but less is known about mixing at the millifluidic scale, especially in a laminar regime. Millifluidic systems, defined as having at least one dimension close to 1 mm in size, represent a class of set-ups important to lab scale production of organic compounds1 and nanoparticles2. Millifluidic systems easily have the capability of producing products on the order of grams per day3, unlike microfluidic set-ups, which due to their inherently small size are unlikely to achieve this level of production. Additionally, specialized fabrication facilities are normally required to manufacture microfluidic devices and typical manufacturing techniques at this scale are not amenable to mass production.
Passive mixers have been well-developed at the microfluidic scale to mix solutions flowing in a laminar regime. In this work we scaled-up the highly utilized groove mixer design4 to mix solutions in a high throughput manner. We first optimized device dimensions using COMSOL and then fabricated the millifluidic mixer by milling polymethylmethacrylate (PMMA) and thermally bonding the milled PMMA to a flat PMMA substrate. We injected dye or fluorescent solutions into the PMMA mixer and quantified the extent of mixing from brightfield and confocal microscope images. Completeness of mixing depended on flow rates and ranged from ~85 – 95% mixing in ~0.25 – 4 seconds. We also quantified the effects on mixing as a result of injecting inlet streams at unequal flow rates and using solutions with viscosities greater than the viscosity of water. Here we have developed and characterized a simple mixer, amenable to mass production, that has the potential to be used in continuous flow millifluidic systems for synthesizing organic compounds and isotropic or anisotropic nanomaterials.
1. V. Dragone, V. Sans, M. H. Rosnes, P. J. Kitson and L. Cronin, Beilstein J Org Chem, 2013, 9, 951-959.
2. Y. Li, A. Sanampudi, V. Raji Reddy, S. Biswas, K. Nandakumar, D. Yemane, J. Goettert and C. S. S. R. Kumar, ChemPhysChem, 2012, 13, 177-182.
3. S. E. Lohse, J. R. Eller, S. T. Sivapalan, M. R. Plews and C. J. Murphy, ACS Nano, 2013, 7, 4135-4150.
4. A. D. Stroock, S. K. W. Dertinger, A. Ajdari, I. Mezic, H. A. Stone and G. M. Whitesides, Science, 2002, 295, 647-651.