Gating characteristics of thermo-responsive and molecular-recognizable membranes based on poly(N-isopropylacrylamide) and β-cyclodextrin

Thermo-responsive and molecular-recognizable membranes with the same functional gate exhibiting triple gating functions are prepared by grafting poly(N-isopropylacrylamide-co-glycidyl methacrylate/β-cyclodextrin) (PNG-CD) chains in the pores of porous Nylon-6 substrate membranes with the combination of plasma-induced pore-filling grafting polymerization and chemical reaction. Morphological and componential analyses of the grafted membranes are confirmed by scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FT-IR). The thermo-responsive and molecular-recognizable gating characteristics of the as-prepared membranes with different grafting yields of poly(N-isopropylacrylamide) (PNIPAM) and β-cyclodextrin (CD) are systematically investigated by examining the diffusional permeability of VB12 molecules through membranes in different conditions with changing environmental temperatures and guest molecules. Experimental results show that, besides reversibly thermo-responsive “open/close” gating performance in response to environmental temperature changing across the lower critical solution temperature (LCST) of the grafted PNG-CD chains in water (e.g., 37 °C ↔ 50 °C), the as-prepared membrane gates can not only switch from “close” to “open” state by recognizing certain guest molecules with a hydrophobic side group (e.g., 8-anilino-1-naphthalenesulfonic acid ammonium salt (ANS)) at temperatures below the LCST of grafted PNG-CD chains in water (e.g., at 37 °C), but also can switch from “open” to “close” state by recognizing different guest molecules with a hydrophilic side group or without side group (e.g., 2-naphthalenesulfonic acid (NS)) in different cases at temperatures above the LCST of PNG-CD in water (e.g., at 50 °C). The thermo-responsive and molecular-recognizable gating characteristics of the as-prepared membranes can be adjusted by changing the grafting yields of both PNIPAM and CD on the membranes as well as the molar ratio of PNIPAM in the grafted chains.