The use of stimuli-responsive polymers in sensing technologies and for actuation has garnered tremendous interest over the past few decades. This is mainly due to the myriad responsivities that these polymers can possess, e.g., responsivity to temperature, pH, biomolecules, CO₂, light, and electricity. As a result, these stimuli-responsive devices can be used to monitor human health and detect environmental analytes, for soft robotics and artificial muscles. In this review, we highlight state-of-the-art examples of the synthesis, and use of stimuli-responsive polymers in these fields that have been reported since 2016.

Superwetting membranes offer a good platform for oil/water separation, but the generation of responsive membranes for on-demand oil/water emulsion separation with both high permeation flux and selectivity is still a challenge. Herein, bilayer membranes that feature asymmetric wettability across the membrane thickness are constructed, simply by depositing a thin layer of polydopamine-coated single-walled carbon nanotubes (SWCNTs) and subsequently coating with a SWCNT layer. When a low applied pressure difference across the membrane, P_applied, is utilized, the hydrophobic–superoleophilic surface is critical for the separation of surfactant-stabilized water-in-oil emulsions. Triggered by an intensive P_applied, surfactant-stabilized oil-in-water emulsions can also be fully separated by a synergistic effect of dual layers. Such ultrathin bilayer membranes exhibit ultrahigh permeation flux and separation efficiency with excellent antifouling for both water-in-oil and oil-in-water emulsion separation in a single-unit, which is readily achieved by the modulation of P_applied. Therefore, we envision that our bilayer membranes show great potential in oil/water emulsion separation.

Single-layered MoS₂-based ultrathin membranes with well-controlled thicknesses are prepared by a simple filtration method, and for the first time applied to gas separation. These membranes exhibit superior H₂/CO₂ separation performance and extremely high H₂ permeance. The H₂/CO₂ separation performance surpasses the state-of-the-art upper-bound of polymeric and inorganic membranes.