Manipulation of liquid transport and droplet switch using light-actuated surface tension

The manipulation of microfluidic systems plays a crucial role in various applications within biology, chemistry, and materials science. However, conventional driving techniques often involve complex setups or rely on external forces, which limits their potential for miniaturization and integration. In this study, we propose a novel method for manipulating microfluidic systems using an azobenzene photosensitive surfactant stimulated by light. This approach offers a simpler and more convenient alternative for controlling microfluidic devices. To demonstrate the effectiveness of our light-driven method, we apply it to control the transition between two bifurcations in a double droplet system (DDS) by surpassing its surface energy barrier. Experimental results demonstrate successful transitions between the bifurcations of the DDS using the light-driven approach. To gain a deeper understanding of the transition process, we establish a dynamic model that considers the surfactant absorption process during the experiment. Furthermore, we provide a simple application of the proposed driving method through a light-activated tunable liquid lens, demonstrating its potential for broader applications in microfluidic systems. This work is expected to contribute to the development of novel light-driven microfluidic manipulation techniques.