Control of the Nanopore Architecture of Anodic Alumina via Stepwise Anodization with Voltage Modulation and Pore Widening

Abstract

Control of the morphology and hierarchy of the nanopore structures of anodic alumina is investigated by employing stepwise anodizing processes, alternating the two different anodizing modes, including mild anodization (MA) and hard anodization (HA), which are further mediated by a pore-widening (PW) step in between. For the experiment, the MA and HA are applied at the anodizing voltages of 40 and 100 V, respectively, in 0.3 M oxalic acid, at 1 °C, for fixed durations (30 min for MA and 0.5 min for HA), while the intermediate PW is applied in 0.1 M phosphoric acid at 30 °C for different durations. In particular, to examine the effects of the anodizing sequence and the PW time on the morphology and hierarchy of the nanopore structures formed, the stepwise anodization is conducted in two different ways: one with no PW step, such as MA→HA and HA→MA, and the other with the timed PW in between, such as MA→PW→MA, MA→PW→HA, HA→PW→HA, and HA→PW→MA. The results show that both the sequence of the voltage-modulated anodizing modes and the application of the intermediate PW step led to unique three-dimensional morphology and hierarchy of the nanopore structures of the anodic alumina beyond the conventional two-dimensional cylindrical pore geometry. It suggests that the stepwise anodizing process regulated by the sequence of the anodizing modes and the intermediate PW step can allow the design and fabrication of various types of nanopore structures, which can broaden the applications of the nanoporous anodic alumina with greater efficacy and versatility.

Iontronic Sensing Based on Confined Ion Transport

“…62−71 Creating a well-ordered alumina nanopore array involves anodizing an aluminum surface. 72 The tunability of pore diameter and density in self-ordered porous anodic alumina is achievable by selecting appropriate anodization conditions such as an electrolyte type, acidity, anodizing voltage, temperature, and time. Additionally, the morphology of the pore on anodized aluminum film is predominantly influenced by the chemical nature of the electrolytes.…”

“…Anodic alumina films, resulting from the electrochemical oxidation of aluminum, have been under scrutiny and application for more than a century. − In the context of confined ion transport, recent focus has shifted toward nanoporous anodic alumina films with a hexagonal arrangement of monodisperse nanopores. This specific structure has gained popularity as a template system for facilitating and investigating ion transport within constrained environments, offering insights into the intricate dynamics of ions within these nanoporous frameworks. − Creating a well-ordered alumina nanopore array involves anodizing an aluminum surface . The tunability of pore diameter and density in self-ordered porous anodic alumina is achievable by selecting appropriate anodization conditions such as an electrolyte type, acidity, anodizing voltage, temperature, and time.…”

Durability of Slippery Liquid-Infused Surfaces: Challenges and Advances

“…Anodization techniques, in which the electrolytic surface oxidation of aluminum or aluminum alloys is performed via a controlled applied voltage, allow the better texturing of porous structures. Surfaces created using this technique also show better shear, thermal and corrosion resistance [110][111][112][113]. Zhang et al [114] developed a facile method for the fabrication of SLIPS using a polyHIPE (poly high internal phase emulsion) membrane as a porous substrate.…”

Engineering Nanoporous Anodic Alumina Bilayered Interferometers for Liquid and Gas Sensing

“…NAA can be precisely engineered using a broad range of anodization and etching approaches to produce various forms of optical systems, including funnel-like structures. − Herein, we present an optical sensing system combining self-organized NAA bilayered Fabry–Perót interferometers (NAA–BFPIs) and RIfS for real-time sensing of ethanol in liquid and gas form (Figure ). NAA–BFPIs composed of a top and a bottom anodic oxide film featuring large and small nanopores, respectively, were fabricated by multi-step anodization combined with chemical etching (Figure a,b).…”