From superhydrophilicity to superhydrophobicity: high-resolution neutron imaging and modeling of water imbibition through porous surfaces treated with engineered nano-coatings

Abstract

This paper reports on a superhydrophilic to superhydrophobic transformation of TiO2 nanoparticles doped zinc phosphate coating systems when a hydrophobic agent is applied. The objective of the reported research was to demonstrate the feasibility of a neutron imaging technique for evaluating the performance of the proposed nano-coating system and reveal the differences in water ingress mechanisms which are specific to plain, superhydrophilic, overhydrophobic, and superhydrophobic specimens. The engineered nano-coatings were designed to improve hydrophobic response with inducing the required roughness pattern and introducing the photocatalytic performance. The effectiveness of the coatings was assessed using high-resolution neutron imaging (HR-NI), SEM, CLSM, and XRD techniques. High-resolution neutron imaging revealed that the superhydrophobic coating effectively prevents water ingress into the porous ceramic substrate, whereas water imbibition was observed for superhydrophilic coating during the test duration. The moisture transport kinetics was modeled based on the Richards equation for plain ceramic and superhydrophilic specimens using obtained penetration depth values from HR-NI. SEM, CLSM, and XRD studies confirm the desired TiO2-doped zinc phosphate coatings with increased surface roughness, photocatalytic reactivity, and chemical bonding. The research results demonstrated that a two-layer superhydrophobic system is capable of creating effective water barriers on the surface with contact angles of 153°, which remained effective even after surface damage.

Advances in green chemistry and engineering

“…Among various coating methods, thin phosphate-based coating combines crucial material protection potential and environmental benefits by repelling water, decomposing organic and inorganic compounds, and providing anticorrosive properties 7 . Zemajtis et al investigated the effect of a hydrophobic agent on the transformation from superhydrophilicity to superhydrophobicity of TiO 2 -doped zinc phosphate coating systems using high-resolution neutron imaging (HR-NI), confocal laser scanning microscope, scanning electron microscope, and X-ray diffraction techniques 8 . The HR-NI showed that water imbibition is observed for the superhydrophilic coating, while water ingress into porous ceramic substrate is prevented by the superhydrophobic coating.…”