Smart Temperature‐Gating and Ion Conductivity Control of Grafted Anodic Aluminum Oxide Membranes

Abstract

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.

A review of stimuli-responsive polymer-based gating membranes

“…Moreover, the thermo-responsive switching of the gates was preserved for three consecutive closed-opened cycles. Very recently, Lee et al 96 reported for a similarly prepared AAO- g -pNIPAM membrane a decrease in resistance with increasing temperature due to the positive gating effect.…”

Surface Modification of Nanopores in an Anodic Aluminum Oxide Membrane through Dopamine-Assisted Codeposition with a Zwitterionic Polymer

“…In recent decades, nanoporous membranes have emerged as versatile platforms with applications across various fields, including biomedical sensing, , nanofiltration, − energy conversion, − and smart separation and gating. − The nanoporous membranes, exhibiting high performance and versatility, usually feature well-controlled nanopore geometries and advanced materials with excellent functionality. ,, Achieving both of these two key characteristics simultaneously often involves surface modification of nanoporous membranes using functional polymer materials, which proves to be a powerful and effective strategy. − Numerous surface modification methods with polymers have been developed based on various interfacial interactions. For example, a simple deposition method is frequently utilized to modify nanoporous membranes by dip or spin coating using polymer solutions, capitalizing on physical interfacial bonding, such as van der Waals forces or hydrogen bonding. , The layer-by-layer assembly method has also been employed for membrane modification through electrostatic interactions with charged polymers. , Additionally, the surface-initiated polymerization method has been introduced to modify membranes with high-grafting density and homogeneous polymer brushes through covalent bonding. − These mentioned traditional surface modification methods, however, usually suffer from issues such as weak bonding, the need for specialized polymer and membrane materials, or complex polymer synthesis techniques, which can limit their applicability for long-lasting usage and mass production development.…”

“…In recent decades, nanoporous membranes have emerged as versatile platforms with applications across various fields, including biomedical sensing, 1 , 2 nanofiltration, 3 − 5 energy conversion, 6 − 8 and smart separation and gating. 9 − 11 The nanoporous membranes, exhibiting high performance and versatility, usually feature well-controlled nanopore geometries and advanced materials with excellent functionality. 8 , 12 , 13 Achieving both of these two key characteristics simultaneously often involves surface modification of nanoporous membranes using functional polymer materials, which proves to be a powerful and effective strategy.…”