Interplay of Local Heating, Nanoconfinement, and Tunable Liquid-Wall Interactions Drive Rapid Imbibition and Pronounced Mixing Between Two Immiscible Liquids.

Designing novel and energy-efficient strategies for disturbing stable interfaces between two immiscible liquids hold the key for a myriad of applications. In this Letter, we propose a highly effective strategy where localized heating (costing less energy) of an interface between two immiscible liquids confined in a nanochannel enable rapid imbibition and mixing between these two liquids. The exact dynamics (imbibition or mixing) depend on the relative wettability of these two liquids to the nanochannel wall. For the case where one liquid is philic and the other is phobic to the nanochannel wall, local heating makes a particular liquid imbibe into the zone occupied by the other liquid with the philic liquid occupying near-wall locations and the phobic liquid occupying the bulk (far wall) positions. The extent of imbibition is quantified in terms of the interfacial thickness between the two liquids, which is found to be larger than the case where the entire system is heated (costing greater energy). We further show that this interfacial thickness can be enhanced by changing the position (along the nanochannel) of localized heating. Finally, we demonstrate that for the immiscible two liquid systems having identical wetting interactions with the wall, the lack of preference of occupying the near wall location by any of the liquids lead to their enhanced mixing in the presence of the localized heating (that imparts additional energy to the liquids enforcing them to cross over to the side of the other liquid).