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Microfluidic technology based on superhydrophobic surfaces
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posted on 22.02.2017by Vuong, An Thach
A water droplet's behaviour on different substrates can vary significantly depending on the surface characteristics. A super hydrophobic surface is unique in that a droplet of water resting on it will exhibit contact angles greater than 1so· and this brings about a variety of benefits, such as low liquid loss due to low adhesive properties. An unexplored application for superhydrophobic surfaces is in microfluidics for 'Lab-on-a-chip' type devices.
In using a sand blaster approach, an intrinsically hydrophobic material such as Teflon was able to be transformed into a superhydrophobic one with contact angles up to 170•. The impact angle of the particulates onto the surface was found to have significant influence on the behaviour modification.
A rod that was made superhydrophobic allowed for direct contact with droplets under low sticking. In microplate wells, this permitted mixing to be done by simple liquid compression. Drops could be delivered to a superhydrophobic well either through the use of a liquid nebuliser, or the continuous delivery of water through a hole at the bottom of the well via a pump. The nebuliser allowed for accurate dispensation of droplets while the pump method offered better opportunities for the creation of a more compact device. The superhydrophobic well could also be used to restrain droplets when it was tilted at different speeds. The angular velocity of the well was found to correlate with the angle in which the droplet would escape the well; the faster the well rotated, the greater the angle required before the droplet would escape. Additionally, with an arrangement of multiple wells on a platform, droplets could be pushed from one well to another using a controlled short bursts of pressurised air.
Overall, it has been found that attributes of superhydrophobic surface, particularly the low adhesion, non-contamination and non-sticking properties, have been shown to offer interesting vistas in discrete microfluidics.