A Waterborne Coating System for Preparing Robust, Self-healing, Superamphiphobic Surfaces

Superamphiphobic surfaces are super-oleophobic and super-hydrophobic making them more preferable than surfaces with super-repellency only to oil or water. These surfaces have been used in applications such as self-cleaning, non-staining surfaces, personal protection, corrosion prevention, antifouling, drag reaction, and liquid separation. For a surface to be superamphiphobicity, it must have high roughness and low surface energy.

A number of methods have been proposed to generate superamphiphobic surfaces including physical etching, template-assisted deposition, roughening surfaces using nanoparticles, and sputter coating. These methods are normally coupled with low-surface-energy treatment.

A number of wet-chemical coating systems for superamphiphobic treatment implement organic solvents including acetone, and ethanol to fabricate the coating solution. Continuous use of organic solvents has environment pollution issues and high preparation cost. Waterborne coating systems have been adopted for superamphiphobic treatment, but remain challenging to make. There are two main obstacles limiting the development of superamphiphobic coating systems. They include preparing a stable dispersion of low-free-energy substances in water and generating durable coating with adequate adhesion to the substrate.

Researchers Dr Hua Zhou and Dr Hongxia Wang led by professor Tong Lin at Deakin University in Australia presented a waterborne coating system that was synthesized by dispersing lyophobic nanoparticles, fluorinated alkyl silane, and fluorocarbon surfactant in water for superamphiphobic treatment for a number of substrates. They demonstrated in their study that a wide range of substrates such as woven and non-woven fabrics, wood, metal, sponge and glass, could be treated through this ternary coating system so as to obtain a superamphiphobic surface with low contact angle hysteresis. Their research work is published in Advanced Functional Materials.

The first author Dr Hua Zhou mentioned that we used either spraying or dip coating to apply the prepared coating solution onto the substrates. In case of soft substrates, for instance, sponge and fabrics, they applied dip coating. We immersed the substrates into the prepared coating solution for approximately two minutes. They were then cured and dried. For the case of hard substrates, for instance, wood plate, metal, and glass slide substrates, we applied spray coating.

The coated substrates indicated durable superamphiphobic surface that could withstand various damages. Coated fabrics were durable against the Martindale abrasion with a 12kPa load. After over 2000 cycles of abrasion, the contact angles of olive oil and water remained high. The authors also tested for abrasion resistance of Zonyl321 coated fabric. This was in a bid to compare the obtained results. After the same abrasion experiment, the fabric samples had several damaged fibers as compared to the polytetrafluoroethylene nanoparticle fluorinated alkyl silane treated samples. They observed that after 2000 abrasion cycles, the Zonyl321 coated fabric turned wettable to both oil and water.

The coated samples could withstand multicycle physical abrasion and washing. Dr Hongxia Wang, a key researcher for this project, indicated that the coating had self-healing ability against chemical and physical damage. This mechanism of synthesis of fully waterborne coating systems is important for the development of cheap, safe superamphiphobic methods for several applications.

The authors were able to prove a stable, waterborne coating solution composed of lyophobic nanoparticles fluorinated alkyl silane, and fluorocarbon surfactant and its application for synthesizing super amphiphobic surfaces. The resulting coating solution can be applied easily onto a number of substrates implementing wet-chemical method.