# Durable Superhydrophobic Composite Coating Based on Hydrangea-like SiO2 Nanoparticles with Excellent Performance in Anticorrosion, Drag Reduction, and Antifouling

## TL;DR

A durable superhydrophobic coating was developed using hydrangea-like SiO2 nanoparticles, showing strong anticorrosion, drag reduction, and antifouling properties for marine and defense applications.

## Contribution

A one-step cold-spraying technique was used to fabricate a durable, hierarchical superhydrophobic coating with excellent mechanical and environmental performance.

## Key findings

- The coating achieved a water contact angle of 170.1° and retained superhydrophobicity after various durability tests.
- It reduced corrosion current density by four orders of magnitude compared to bare aluminum.
- The coating achieved a maximum drag-reduction rate of 31.01% in water flow tests.

## Abstract

Superhydrophobic coatings possess distinct wettability characteristics and hold significant potential in metal corrosion protection and underwater drag reduction. However, their practical application is often hindered by poor durability arising from the fragility of their micro/nanostructured surface roughness. In this study, a durable superhydrophobic coating featuring a hierarchical, hydrangea-like micro/nanostructure was successfully fabricated on an aluminum alloy substrate via a simple one-step cold-spraying technique. The coating consisted of hydrangea-shaped SiO2 nanoparticles modified with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDT) to produce multiscale roughness, while epoxy resin (EP) served as the binding matrix to enhance mechanical integrity. The hydrangea-like SiO2 nanostructures were characterized by solid cores and wrinkled, petal-like outgrowths. This unique morphology not only increased the surface roughness but also provided more active sites for air entrapment, thereby enhancing the coating’s overall performance. The h-SiO2@PFDT-EP composite coating exhibited excellent superhydrophobicity, with a WCA of 170.1° ± 0.8° and a SA of 2.7° ± 0.5°. Durability was evaluated through sandpaper abrasion, tape peeling, acid and alkali immersion, artificial weathering, and salt spray tests. The results demonstrated that the coating retained stable superhydrophobic performance under various environmental stresses. Compared with bare 6061 aluminum and EP coatings, its corrosion current density was reduced by four and three orders of magnitude, respectively. Furthermore, the coating achieved a maximum drag-reduction rate of 31.01% within a velocity range of 1.31–7.86 m/s. The coating also displayed excellent self-cleaning properties. Owing to its outstanding durability, corrosion resistance, and drag-reducing capability, this one-step fabricated superhydrophobic coating showed great promise for applications in marine engineering and defense.