Control fluids in tiny places

Philips Research Laboratories in Eindhoven has developed a new technology that allows the motion of fluid to be controlled in three-dimensional structures.

The company says that the development opens exciting possibilities in applications ranging from optical switches and filters to printing technologies and (bio)chemical synthesis and analysis in lab-on-a-chip devices.

The technology is based on controlling the position and motion of fluids inside a microchannel by electrically adjusting the magnitude of the capillary effect. The inner wall of the microchannel is coated with an electrode and separated from the fluid by an insulating layer. In this way, a capacitor is formed with the fluid as the second electrode.

By charging and discharging the capacitor, the interfacial tension between the fluid and the wall can be adjusted, and this determines the position of the fluid. By using a network of channels, downscaling the dimensions and applying a matrix of control electrodes, a structure arises in which the position of fluids can be electrically and reversibly controlled in three dimensions and at a micrometer scale.

Because this so-called ‘electrocapillary pressure (ECP)’ method does not involve mechanically moving parts, it is inherently reliable and consumes little power. The velocity of the fluid is up to hundred times higher than that which can be achieved by alternative nonmechanical and electrical methods.

Important benefits can be realised in the rapidly growing field of micro(bio)chemical synthesis and analysis in so-called lab-on-a-chip devices. In these chips a small fluidic sample volume is directed through networks of channels and distributed across a large number of probe locations. In present-day devices the motion of fluids is controlled by tuning the channel dimensions and by external pumps. With the ECP technology, much more accurate, complex and flexible chips become feasible.

Heating effects and space requirements are important limitations in the miniaturisation of present-day inkjet printer heads. The direct control of fluid motion with ECP technology opens up the possibility of integrating a multitude of nozzles in a single printer head for higher resolution and higher printing speeds.

Other options arise in optical products. By changing the position or amount of fluid inside the network of microchannels, the optical properties (such as transparency, reflectivity or absorption of light) can be controlled and varied locally. This can be applied to switch optical signals in telecom applications, or to spatially filter x-rays for a better image quality and a lower required radiation dose in medical x-ray imaging.