Solubility-Gated Marangoni Actuation Enables Vapor-Based Droplet Manipulation

Digital microfluidics enables programmable manipulation of microscale droplets for applications ranging from biochemical assays to adaptive displays. While electrowetting on dielectric (EWOD) is widely used for its fast voltage-based control, it requires high energy input and suffers from material degradation, limiting long-term efficiency and scalability.

In this work, we present a low-energy, electricity-free alternative based on vapor-driven Marangoni actuation. By exposing the droplet interface to a controlled vapor field, we introduce interfacial tension gradients that generate directional flow and deformation without direct contact or applied voltage. A key challenge in vapor-based control lies in undesired vapor absorption into the droplet, which hinders reversibility and stability. To address this, we systematically investigated vapor sources with varying solubility in the base fluid. Our results exhibit that utilizing low-solubility vapor sources yields strong Marangoni flows with minimal absorption, enabling rapid and stable droplet responses. This principle is demonstrated in a prototype liquid-based pixel array for display applications. Our results establish solubility-gated Marangoni flow as a robust mechanism for droplet manipulation and offer a scalable, energy-efficient platform for next-generation digital microfluidics.