Comprehensive Comparison of Anodic Alumina Membrane Infiltration Methods: Electrolyte Selection, Membrane Stability and Flow Rate Characterization

Dr. Irina Oliseveca presented a poster entitled, "Comprehensive Comparison of Anodic Alumina Membrane Infiltration Methods: Electrolyte Selection, Membrane Stability and Flow Rate Characterization".

Abstract:

Nanoporous anodic aluminum oxide (AAO) is one of the most popular and cost-effective platforms for various applications from molecular separation to drug delivery and energy generation. Its unique optical and electrochemical properties are extensively explored for biosensing and energy-harvesting applications. One of the main challenges in the effective application of AAO membranes in different devices involving liquid media is control of the nanopore filling and percentage of the active nanopore channels.

In this work, 50 mm thick AAO membranes with pore diameters 25 nm and 40 nm were fabricated using the two-step anodization in oxalic and sulfuric acids and infiltrated with aqueous electrolytes (NaCl, NaClO₄, Na₂SO₄) by different infiltration methods. The concentration of the solution varied from 10^-6 mol/dm³ to 1 mol/dm³. The percentage of infiltrated nanochannels was controlled using electrochemical impedance spectroscopy (EIS) measurements. The morphology of the membranes before and after infiltration was characterized using scanning electron microscopy (SEM). 

A comprehensive analysis of different infiltration methods for nanoporous AAO membranes with aqueous electrolytes was carried out, and the advantages and drawbacks of each filling method were identified. Between the studied methods, the hydrostatic pressure-induced infiltration technique was determined as the most effective method for filling more than 90% of the pore channels.

The dependence of filtration rate on electrolyte concentration was determined for both types of AAO membranes. The changes in the filtration rate can be used to indicate the occurrence of damaging/degradation processes in AAO pore channels. The dependence of solution flow rate or AAO membrane resistance per unit of the active area of the membrane on electrolyte concentration can be used to investigate the contribution of electrokinetic effects that occur in nanochannels and are especially noticeable when electrical double layers along the inner walls of the nanopores are completely or partially overlapped.