Actuation of Janus Emulsion Droplets via Optothermally Induced Marangoni Forces
Sara Nagelberg, Jan Frederik Totz, Matthäus Mittasch, Vishnu Sresht, Lukas Zeininger, Timothy M. Swager, Moritz Kreysing, Mathias Kolle
Abstract
Microscale Janus emulsions represent a versatile material platform for dynamic refractive, reflective, and light-emitting optical components. Here, we present a mechanism for droplet actuation that exploits thermocapillarity. Using optically induced thermal gradients, an interfacial tension differential is generated across the surfactant-free internal capillary interface of Janus droplets. The interfacial tension differential causes droplet-internal Marangoni flows and a net torque, resulting in a predictable and controllable reorientation of the droplets. The effect can be quantitatively described with a simple model that balances gravitational and thermal torques. Occurring in small thermal gradients, these optothermally induced Marangoni dynamics represent a promising mechanism for controlling droplet-based micro-optical components.