Bioinspired dual stimuli-responsive membranes with enhanced gating ratios and reversible performances for water gating

Self-regulation of membrane permeability performance is highly desirable for porous membrane applications. Inspired by the stomatal closure behaviour of plant leaves in response to environmental changes, here we report a series of dual thermo- and pH-responsive membranes based on the poly(4-vinyl pyridine) (P4VP) core/poly(N-isopropylacrylaminde) (PNIPAM) shell microgels. The stimuli-responsive microgels underwent in situ surface segregation and uniformly decorated on the surface of internal channels during the phase inversion process. The hydraulic permeability performance of the dual responsive membranes (DRMs) has been investigated within a temperature range of 20–50 °C and a wide pH range (spanning pH 2–6). The water flux of optimized membrane (M2) varied from 1.94 kg m−2 h−1 at 20 °C/pH 2–474.91 kg m−2 h−1 at 50 °C/pH 6 with a high gating ratio of 245. Investigations revealed that microgels based on different thickness of PNIPAM shell conferred different thermo-/pH-responsive properties to the DRMs. For example, the thicker PNIPAM shell enhanced the thermo-response performance, while the pH-response performance was restrained. These optimum smart gating membranes with enhanced gating coefficient and reversibility are potential for the applications in water gating and controlled release systems.