Description
Liquid–liquid interfaces are central to open microfluidics, yet programming interfacial mass transfer and reading out droplet motion or flow history without embedded hardware or tracer particles remains challenging. We present a liquid crystal (LC) platform in which water droplets interacting with LC films – by impact or translation – control liquid–liquid transport while simultaneously generating optically readable textures that encode the droplet’s mechanical footprint and pathway [1-4].
Droplet impact on LC films provides a direct route to controlling water–LC exchange through the coupled roles of LC mesophase order and impact-driven interfacial deformation. By tuning the LC state and impact conditions, both the magnitude and direction of liquid–liquid mass transfer can be regulated within the same material system [3]. This impact-mediated mechanism also enables a droplet-based printing concept in which collision triggers the release of highly viscous cargo from an LC film onto an LC receiving surface, extending droplet impact approaches beyond conventional inkjet-compatible viscosity ranges.
Droplet motion can also write a persistent record of its pathway when the LC film is micropatterned [4]. In a hexagonal lattice of micrometer-scale pillars with homeotropic anchoring, confinement stabilizes elastic dipole–pillar pairs that form disordered polar textures under water. When a water droplet moves across this structured LC interface, interfacial shear realigns dipoles cooperatively into stable domains. The resulting textures encode droplet direction and trajectory, providing a label-free method to reconstruct microscale flow histories by polarized optical microscopy.
Overall, these results establish LC films as reconfigurable open microfluidic media in which droplet impact and translation enable programmable liquid–liquid transport and topological recording of droplet pathways, offering a versatile basis for adaptive printing, interfacial processing, and flow diagnostics.
- [1] Y. Xu et al, Sci. Adv. 7, eabi7607 (2021).
- [2] Y. Xu et al, Nano Res. 16, 5098 (2023).
- [3] Y. Xu, M. Zhang, R. Štanc, et al, to be published.
- [4] U. I. Kara, B. Chen, S. Čopar, et al, Nature Phys. 21, 1404 (2025).