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

SA Etha and S Das, JOURNAL OF PHYSICAL CHEMISTRY B, 127, 5959-5966 (2023).

DOI: 10.1021/acs.jpcb.3c01353

Nanoconfinement is known to drive phase separation (oftendenotedas microphase separation) of two highly miscible liquids by subjectingthe two liquids to disparate influences. Here, we propose a paradigmshift to this problem: we introduce the idea of "repeatability"in nanoconfinement-driven microphase separation. A drop consistingof two highly miscible liquids (A and B) is made to pass through ananochannel grafted with a collapsed layer of polymer that is philicto A but phobic to B. Subsequently, a significant number of moleculesof liquid A get imbibed into the polymer layer and the polymer layerpartially swells, while the molecules of liquid B mostly remain outof the polymeric layer and are carried away, emerging as a drop onthe other side of the polymer bilayer. This passage of drop (of liquidsA and B) is continued, and each time liquids A and B get separatedwith liquid A imbibing into the polymer layer and liquid B being carriedaway with the drop. This scenario, therefore, points to the repeatedoccurrence of the microphase separation of miscible binary liquidmixtures, enabling the processing of a much larger volume of liquid,given the fact that the presence of a grafted polymer layer continuesto provide a dynamically increasing space where liquid A can get localizedafter being separated from liquid B. We quantify such repeated microphaseseparation by noting the extent of separation (of liquid A) and extentof recovery (of liquid B) as functions of nanochannel height and numberof passes. Interestingly, we establish that this process also leadsto a distillation-like behavior (without any heat addition), wherethe concentration of liquid B (equivalent to the "less volatile"liquid in a standard distillation process) progressively increasesinside the drop after its passage through the nanochannel.

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