Micromixing devices are an essential feature of many microfluidic systems and are used to homogenise samples or reaction components. However viscous effects greatly diminish mixing which is dominated by molecular diffusion rather than turbulence on the microscale. Micromixers based on external energy sources such as pressure, electrical or acoustic energy can be used to accelerate mixing but they are complicated, hard to fabricate and require power supplies. There is therefore an urgent need for a micromixer which is simple, efficient, stable, robust, easily integrated into a larger system free of external power supplies. The key issue is that if random processes such as diffusion and turbulence are ineffective the only option is to understand where the molecules are going and to design a micromixer based on chaotic mixing and chaotic advection. Recently two applied mathematicians at the University of Bristol (Prof Steve Wiggins and Dr Rob Sturman) have successfully employed dynamical systems theory, in particular the Linked Twist Map and ergodic theory, to understand the problem of micromixing at a more abstract and fundamental level. As a result of this insight it has been possible to design new optimised micromixers which have chaotic particle trajectories over the whole region where mixing is required. Such micromixers have a significant reduction in islands of unmixed fluid and therefore achieve much more efficient mixing. The key advantages of the Bristol micromixer technology are therefore as follows (i) Design methodology can be used to optimise a wide class of chaotic micromixer. (ii) Optimised mixing is achieved which is more rapid, stable, reproducible and accurate. (iii) Micromixer designs can be adjusted and then rapidly re-optimised.
(PCT patent application PCT/GB2007/001775) and related US and European applications
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