Wetting transition of the ordered nanoporous matrix layer under impact and static pressure

In this study, a series of anodic aluminum oxide (AAO) ordered nanoporous matrix layers were prepared, and hydrophobic (perfluoroalkyltriethoxysilanes, PFO) and hydrophilic (3-aminopropyltrimethoxysilane, APTS) materials were modified on these surfaces. The static contact angle of these specimens was in the range of 30-153°. By using the f values in the theory equation and comparing with the experiment value, the wetting state of the surface was determined. Under impact pressure, the wetting states of the porous surface with the hydrophobic PFO-modified material were more stable, and the contact angle on these surfaces under external pressure remains constant. However, the hydrophobicity of the surface modified with APTS was metastable, and the surface hydrophobicity decreased as the impact pressure increased. Under sufficient hydraulic pressure, the liquid would wet a rough structure, and the hydrophobic state would be lost and not automatically restored. In addition, the change in the wettability of the APTS-modified surface occurs spontaneously due to the immersion conditions. Finally, the critical pressure of the PFO-modified surfaces was investigated. Although the critical pressure of the surface is on the micrometer level, which is similar to the static energy barrier (ΔP), our experimental data are smaller and on the nanometer scale, which is discussed in this study.