Two dimensional thermoelectric platforms for thermocapillary droplet actuation

Thermocapillary droplet actuation on a substrate is based on the mechanism that droplets can be driven to the cooler regions via surface tension modulation by varying the temperature. The usual method of providing a temperature gradient or temperature difference for thermocapillary droplet actuation is via resistor heaters, in which the rise in temperature can be achieved by increasing the passing currents, yet the cooling function relies on the natural conduction and/or convection. A thermoelectric (TE) chip is advantageous in the temperature control. The heating and cooling functions can be manipulated simply by adjusting the direction of the input current into the TE chip. In this regard, the temperature setting can be precisely feedback-controlled by manipulating the amplitude and direction of current flows. This paper demonstrates the implementation of a two dimensional (2D) TE array for free-surface thermocapillary droplet actuation. The routing, merging, and cutting of droplets are successfully demonstrated on a hydrophobically patterned glass substrate overlaid on the TE array.