Permeation-induced flows: Consequences for silicone-based microfluidics

The permeation properties of water through silicone elastomers have been studied in microfabricated channels. This effect, negligible for most macroscopic systems, generates flows in silicone- based microfluidic structures that can be strong enough to become a major concern. By observing the motion of tracers in channels of various geometries, these flows have been quantitatively measured and the average velocity has been shown to be roughly inversely proportional to the section of the channel. This effect can be advantageously used to concentrate colloids and in some cases to crystallize these particles.