Repeated Microphase Separation and Heating-free Distillation-like Behavior of Miscible Binary Liquid Mixtures Using Nanoconfined Grafted Polymer Layers.

Nanoconfinement is known to drive phase separation (often denoted as microphase separation) of two highly miscible liquids by subjecting the two liquids to disparate influences. Here, we propose a paradigm shift to this problem: we introduce the idea of "repeatability" in nanoconfinement-driven microphase separation. A drop consisting of two highly miscible liquids (A and B) is made to pass through a nanochannel grafted with a collapsed layer of polymer that is philic to A but phobic to B. Subsequently, a significant number of molecules of liquid A get imbibed into the polymer layer and the polymer layer partially swells, while the molecules of liquid B mostly remain out of the polymeric layer and are carried away, emerging as a drop on the other side of the polymer bilayer. This passage of drop (of liquids A and B) is continued, and each time liquids A and B get separated with liquid A imbibing into the polymer layer and liquid B being carried away with the drop. This scenario, therefore, points to the repeated occurrence of the microphase separation of miscible binary liquid mixtures, enabling the processing of a much larger volume of liquid, given the fact that the presence of a grafted polymer layer continues to provide a dynamically increasing space where liquid A can get localized after being separated from liquid B. We quantify such repeated microphase separation by noting the extent of separation (of liquid A) and extent of recovery (of liquid B) as functions of nanochannel height and number of passes. Interestingly, we establish that this process also leads to a distillation-like behavior (without any heat addition), where the concentration of liquid B (equivalent to the "less volatile" liquid in a standard distillation process) progressively increases inside the drop after its passage through the nanochannel.