Micromixer fabrication

Lee S, Kim D, Lee S, Kwon T (2006) A split and recombination micromixer fabricated in a PDMS three-dimensional structure. J Micromech Microeng 16 1067. http //dx.doi.org/... 

Numerous fabrication techniques have been used for making micromixers. In the past few years, there have been two obvious developments in micromixer fabrication the substrate was changed from silicon to polymers and the structures were changed from simple planar structure to complex 3D structure. Most of the early micromixers were fabricated in silicon. The mixing channels were either wet etched with KOH [16, 35, 42, 52, 53, 66] or dry etched using DRIB (deep reactive ion etching) [23, 26, 31, 37, 45, 54, 59, 96]. Anodically bonded glass on top of the channel... 

The use of PDMS tools can also be extended to fabrication of multi-height stractures [24]. This is schematically shown in Fig. 13a. The process involves two lithography steps, (e. g., one with SU-8 and one with AZP 4620 photoresists). A passive micromixer fabricated using this process is shown in Fig. 13b. The mixing channel width is 200 pm at the widest point and 100 pm at the narrowest, with diamond obstructions 100 pm in width. Channel height is 55 pm with 15 pm high obstructions. 

Figure 2.2 A simple fabrication process of active electrokinetically driven micromixers, (a) BOE etching, (b) electron beam evaporation of gold/chromium, (c) gold/chromium etching, (d) cover drilling, and (e) alignment and bonding [62].

Fig. 5. Single mixer and micromixer array in nickel on copper fabricated by LIGA technique and housing. Channel width 40 pm, Materials Nickel on copper, silver and titanium diboride. The silver and nickel-on-copper micromixers were realized by electroforming, the titanium diboride micromixer was fabricated by die sinking with LIGA electrodes...

Although T-shaped micromixers are very simple in structure and are easy to fabricate by conventional mechanical machining technology, they can be very effective in achieving fast mixing (Figure 7.14). At a low flow... 

On the other hand, passive chaotic micromixers typically use complex three-dimensional twisted conduits fabricated in various substrates such as silicon [13], polydimethylsiloxane (PDMS) [14], ceramic tape [15], or glass [13] to create 3-D steady flow velocity with a certain complexity to achieve chaotic advection. T q)ical examples of the aforementioned two routes to achieve chaotic advection and mixing in LOC devices are presented in the following. 

N.T. Nguyen, Micromixers Fundamentals, Design and Fabrication, William Andrew Micro Nano Technologies Series (2008). 

The problem of spontaneous separation of micromixer-produced droplets was investigated using dodecane and water as the model system [33]. To enhance spontaneous separation the emulsion from the micromixer was fed into a rectangular channel fabricated from aluminum foil as a spacer between two flat plates of glass and/or PTFE. In the case of PTFE coalescence occurred readily whereas glass did not promote the separation. This study demonstrated that the wall material and its surface properties (wettability) can have a big influence on coalescence behavior. 

Chaotic mixing based on viscoelastic flow instability in rather simple microfluidic channel geometries was successfully demonstrated. These viscoelastic micromixers bypass the limitation of low Reynolds number in microfluidic flows and could potentially be implemented in a Lab-on-a-Chip platform with minimum requirements for design and fabrication. However, this type of micromixer is yet to be optimized. 

Another blood analysis device has recently been described by Ahn and colleagues [3]. Since blood typing is a critical procedure required for blood transfusions, the researchers fabricated an inexpensive disposable microdevice to rapidly determine blood type. This system is composed of integrated sample entry channels, micromixers for mixing the... 

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