Engineering Dual CO 2 - and Photothermal-responsive Membranes for switchable Double Emulsion Separation.

Stimulus-responsive membranes demonstrate promising applications in switchable oil/water emulsion separations. However, they are unsuitable for the treatment of double emulsions like oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions. For efficient separation of these complicated emulsions, fine control over the wettability, response time, and aperture structure of the membrane is required. Herein, dual-coated fibers consisting of primary photothermal-responsive and secondary CO 2 -responsive coatings were prepared by two steps. Automated weaving of these fibers produced membranes with photothermal- and CO 2 -responsive characteristics and narrow pore size distributions. These membranes exhibited fast switching wettability between superhydrophilicity (under CO 2 stimulation) and high hydrophobicity (under near-infrared stimulation), achieving on-demand separation of various O/W/O and W/O/W emulsions with separation efficiencies exceeding 99.6%. Two-dimensional low-field nuclear magnetic resonance and correlated spectra technique were employed to clarify the underlying mechanism of switchable double emulsion separation. Our approach can effectively address the challenges associated with the use of stimulus-responsive membranes for double emulsion separation and facilitate the industrial application of these membranes. This article is protected by copyright. All rights reserved.