Dancing droplets on a wire

Dancing droplets on a wire

Chair: Physics of Complex Fluids

Traditional microfluidics is concerned with the transport of small liquid volumes within microchannels. In this assignment, we would like to introduce a new method for moving small droplet volumes, namely on a wire. On a wire, the small liquid volumes can be transported, merged, divided, and mixed (see Figure 1) [1]. To control these droplet operations, we use electrowetting [2].

For the droplet operations, wettability is an important parameter. The wettability can be expressed as the angle that the droplet makes with the wire. By using electrowetting, we apply an electric field to the droplet to change this contact angle, and thereby the mobility of the droplets. We have shown that we can tune the droplets reversibly from a mobile (asymmetric) clamshell state to a less mobile (axisymmetric) barrel state (see Figure 2) [3].

The goal of this project is to investigate experimentally how the drop morphologies (changed by electrowetting) play a role in the transport and mixing of droplets on a wire. You will develop an experimental system, and will measure the influence of electro-wetting on transport velocities and mixing rates, using image analysis (Matlab). Further, you will learn about general wetting theory, capillarity, electrowetting, and energy considerations dictating morphological transitions.

Figure 1. Microfluidic operations on a wire (adapted from Figure 2. (A) Barrel and (B) clamshell

[1]). droplet.

[1] Gilet et al., Appl. Phys. Lett. 95 (2009), 014106

[2] Mugele and Baret, J. Phys.: Condens. Matter 17 (2005), R705-R774

[2] Eral et al., DOI: 10.1039/c0sm01403f





Tutor: Burak Eral

Riëlle de Ruiter, Jolet de Ruiter




Teacher: Frieder Mugele