pH-Responsive Shape Memory Porous Foam for Intelligent On-Demand Separation of Various Oil-Water Systems

Although intelligent superwettability materials with tunable wettability have been extensively studied in oil-water separation, they still exhibit several limitations including singular dimension of response, nondurable surface modification, and inadequate on-demand separation capabilities. Herein, we propose an ingenious strategy that combines pH-responsive polymer and shape memory material to achieve intelligent dual-regulation of surface wettability and pore size. A porous double-regulated foam (DRF) is obtained by uniformly mixing epoxy resin with PMMA-co-PDEAEMA solution and one-piece curing it through salt template method. Simple immersion in acidic (pH = 2) and alkaline (pH = 13) solutions can transform the wettability of DRF30 (where 30 represents the mass ratio of pH-responsive polymer) between high hydrophobicity/superoleophilicity and superhydrophilicity/underwater superoleophobicity. As the temperature rises (130 °C) and cools, DRF30 also stably undergoes shape memory compression and recovery, switching pore size between 150 and 1.52 μm, with partial apertures being reducible to the nanoscale. Thus, DRF30 is endowed to separate oil-water mixtures with high flux (>1300 L m^-2 h^-1) in uncompressed state and emulsions to ensure separation efficiency (>99.5%) in compressed state, further incorporating changes in wettability to enable on-demand separation of various oil-water systems. Moreover, after conducting five double-regulation cycle tests and stability assessments, DRF30 consistently maintains outstanding separation performance, demonstrating commendable durability and physicochemical stability. This novel strategy shows guiding significance in smart material design and intelligent on-demand oil-water separation applications.