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We report herein the design and preparation of microgels that are responsive to both O2 and CO2 gases. The microgels were synthesized through soap-free emulsion copolymerization of O2-responsive monomer 2,3,4,5,6-pentafluorostyrene (FS) and CO2-responsive monomer 2-(diethylamino)ethyl methacrylate (DEA) with N,N'-methylenebis(acrylamide) (BisAM) as the cross-linker. The P(DEA-co-FS) microgels dispersed in aqueous solution could undergo volume phase transitions triggered by O2 and/or CO2 aeration. The particles were very responsive to CO2, while their responsivity to O2 was moderate. Microgels having different levels of the responsivity could be designed and prepared by varying the FS content in the copolymer. The phase transitions were also highly reversible, and the initial states of microgels could be easily recovered by "washing off" the trigger gases with N2. Multicycle O2, CO2, and N2 aerations were applied, and no loss in the dual gas responsivity and switchability was observed.

Polymer membranes with switchable wettability have promising applications in smart separation. Hereby, we report highly porous poly(styrene-co-N,N-(diethylamino)ethyl methacrylate) (i.e., poly(St-co-DEA)) membranes with "open-cell" structure and CO-switchable wettability prepared from water-in-oil (W/O) high internal phase emulsion (HIPE) templates. The open-cell porous structure facilitates fluid penetration through the membranes. The combination of CO-switchable functionality and porous microstructure enable the membrane with CO-switchable wettability from hydrophobic or superoleophilic to hydrophilic or superoleophobic through CO treatment in an aqueous system. This type of membrane can be used for gravity-driven CO-controlled oil/water separation, in which oil selectively penetrates through the membrane and separates from water. After being treated with CO switching wettability of the membrane, a reversed separation of water and oil can be achieved. Such a wettability switch is fully reversible, and the membrane could be regenerated through simple removal of CO and oil residual through drying. This facile and cost-effective approach represents the development of the first CO-switchable polyHIPE system, which is promising for smart separation in a large volume.

A large number of gold nanoparticles (ca. 3.8 nm in diameter) were homogeneously and effectively incorporated into thiol-functionalized poly(N-isopropylacrylamide) (PNIPAM) microgels through the well-known Au-thiol chemistry. Here, the thiol-functionalized PNI-PAM microgels were obtained by carbodiimide-mediated amide bond formation between the carboxyl-functionalized PNIPAM microgels and 2-aminoethanethiol. The prepared PNIPAM-Au hybrid microgels exhibited well-defined thermally modulated optical and catalytic properties.