Programmable Inter-Droplet Communication by Polymer-Gated Ion Transport Through Nanopore Lattices.

Owing to their hydrophilicity and pronounced capillary pressures, mesoporous platforms enable isotropic or multidirectional fluid transport. Based on aqueous salt solution droplets, we investigate nanopore-driven ion transport control for tailorable droplet communication via a mesoporous surface. Droplets were placed on a mesoporous silica thin film, separated by a polyelectrolyte (PEL) barrier. The PEL-barrier was incorporated into the mesoporous matrix by automated direct-laser-writing and a grafting-from SI-PET-RAFT polymerization. Permselective transport-regulated barrier breakthrough times were used to compare aqueous BaCl2, MgSO4, MgCl2, and NaCl solutions. By tuning the barrier widths, the full range of the polyelectrolyte barrier functions from ion-selective flow regulation to complete fluid retention becomes attainable. Ion-specific barrier interactions lead to characteristic imbibition dynamics beyond the barrier, involving advancing imbibition toward a steady state in the case of favored barrier permeation, or hindered and oscillating imbibition in the case of disfavored barrier permeation. The ionic selectivity further allows the emergence of control of chemical events such as precipitation reactions in nanopores by the spatial localization of droplets according to the barrier site. The insights into polyelectrolyte-regulated ion transport during imbibition processes bring new tools for the development of compartmentalized and reconfigurable communication between distant fluid reservoirs through nanostructured coatings.