Over the past few decades, stimuli-responsive materials have been widely applied to porous surfaces. Permeability and conductivity control of ions confined in nanochannels modified with stimuli-responsive materials, however, have been less investigated. In this work, the permeability and conductivity control of ions confined in nanochannels of anodic aluminum oxide (AAO) templates modified with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes are demonstrated. By surface-initiated atom transfer radical polymerization (SI-ATRP), PNIPAM brushes are successfully grafted onto the hexagonally packed cylindrical nanopores of AAO templates. The surface hydrophilicities of the membranes can be reversibly altered because of the lower critical solution temperature (LCST) behavior of the PNIPAM polymer brushes. From electrochemical impedance spectroscopy (EIS) analysis, the temperature-gating behaviors of the AAO-g-PNIPAM membranes exhibit larger impedance changes than those of the pure AAO membranes at higher temperatures because of the aggregation of the grafted PNIPAM chains. The reversible surface properties caused by the extended and collapsed states of the polymer chains are also demonstrated by dye release tests. The smart thermo-gated and ion-controlled nanoporous membranes are suitable for future smart membrane applications.[a] M.
Regular arrays of anisotropic polymer nanomaterials have attracted great attention because of their unique properties and various applications such as solar cell devices, sensors, and supercapacitors. The control of the shape manipulation and tailored properties of individual polymer nanomaterials in arrays, however, remains a great challenging task. In this work, we demonstrate a versatile approach to fabricate elliptical and bent polymer nanorod arrays through laser-induced photo-fluidization of azobenzene-containing polymers (azopolymers). Ordered anodic aluminum oxide (AAO) membranes are used as templates for generating azopolymer nanorod arrays via a solvent vapor annealing-induced wetting method. After being released from the AAO templates and shone by linearly polarized lights, the nanorod arrays can be transformed into anisotropic nanostructures, driven by the trans-to-cis and cis-to-trans isomerization of the azobenzene groups in the azopolymers. Depending on whether the laser beam is shone at normal or tilt angles of incidence, elliptical or bent nanorod arrays can be prepared, respectively. The deformation degrees and water wettabilities of the nanorod arrays can be varied by changing the illumination times. This study reports a beneficial route to prepare ordered arrays of anisotropic polymer nanostructures for advanced applications.
Toxic agricultural pollutants in the environment, such as paraquats, are harmful to human beings. In this study, we provide a feasible method for sensing three kinds of paraquat derivatives. Anodic aluminum oxide (AAO) membranes are used as substrates to detect paraquat derivatives owing to their properties of highly porous structures and chemical stabilities. After pyranine molecules are chemically modified on the surface of AAO templates, pyraninegrafted AAO (P-AAO) membranes are obtained, which can be used for sensing paraquat derivatives by π−π electron stacking interactions, Coulombic attractions, and charge-transfer interactions. The changes of absorption intensities in ultraviolet−visible (UV−vis) spectra and alternations of impedance in Nyquist plots are observed by sensing the paraquat derivatives with P-AAO membranes. The P-AAO membranes show remarkable sensibility and immediacy during the processes of sensing paraquat derivatives, and the limit of detection (LoD) reaches 0.9 μM. This work successfully demonstrates that P-AAO membranes can be an excellent choice for detecting pollutants in the environment and industry.
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