Regulation of Critical Ethanol Response Concentrations of Ethanol-Responsive Smart Gating Membranes

Regulation of the critical ethanol response concentration of ethanol-responsive smart gating membranes has been systematically investigated by preparing a series of gating membranes with grafted poly(N-isopropylacrylamide) (PNIPAM) and PNIPAM-based copolymer gates. A porous Nylon-6 (N6) membrane is used as the substrate membrane, and the surface-initiated atom transfer radical polymerization (ATRP) method is employed to graft polymers onto the substrate membrane. Fourier Transform Infrared Spectrometer (FT-IR) is used to determine chemical compositions of the prepared membranes, and Scanning Electron Microscope (SEM) is used to investigate the microstructures of membranes. The fluxes of ethanol solutions across different membranes are studied systematically by changing the ethanol concentration. The results show that the introduction of hydrophilic monomer N,N-dimethylacrylamide (DMAA) or hydrophobic monomer butyl methacrylate (BMA) into the grafted PNIPAM-based gates can effectively regulate the critical ethanol response concentration of the gating membranes. The quantitative relationships between the critical ethanol response concentration of the grafted membranes and the lower critical solution temperature (LCST) in water of the PNIPAM-based functional gates are summarized in this study for the first time, by which the critical ethanol response concentration of the grafted membranes can be effectively predicted. The results provide valuable guidance for designing and preparing ethanol-responsive gating membranes with adjustable critical ethanol response concentrations by simply regulating the LCST in water of the grafted PNIPAM-based gates and controlling the operation temperature.