Effect of Ageing on the Structure and Properties of Model Liquid-Infused Surfaces.

Sarah J Goodband,Kislon Voı̈Tchovsky,Halim Kusumaatmaja,Steven Armstrong

doi:10.1021/acs.langmuir.0c00059

Sarah J Goodband, Kislon Voı̈Tchovsky + Show 2 more

Open Access

https://doi.org/10.1021/acs.langmuir.0c00059

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Abstract

Liquid-infused surfaces (LISs) exhibit unique properties that make them ideal candidates for a wide range of applications, from antifouling and anti-icing coatings to self-healing surfaces and controlled wetting. However, when exposed to realistic environmental conditions, LISs tend to age and progressively lose their desirable properties, potentially compromising their application. The associated ageing mechanisms are still poorly understood, and results reflecting real-life applications are scarce. Here, we track the ageing of a model LIS composed of glass surfaces functionalized with hydrophobic nanoparticles and infused with silicone oil. The LISs are fully submerged in aqueous solutions and exposed to acoustic pressure waves for set time intervals. The ageing is monitored by periodic measurements of the LIS’s wetting properties. We also track the changes to the LIS’s nanoscale structure. We find that the LISs rapidly lose their slippery properties because of a combination of oil loss, smoothing of the nanoporous functional layer, and substrate degradation when directly exposed to the solution. The oil loss is consistent with water microdroplets entering the oil layer and displacing oil away from the surface. These mechanisms are general and could play a role in the ageing of most LISs.

Highlights

Liquid-infused surfaces (LISs) represent a family of functional surfaces inspired by the Nepenthes pitcher plant whose porous outer surface is imbibed with a lubricating liquid
In order to objectively and systematically investigate the ageing of the model LISs, we have organized the study in three consecutive parts
To maximize the practical relevance of our findings, we use a model LIS made with a commercially available spray of hydrophobized silica NPs (GLACO, see the Experimental Methods section), which creates a porous nanolayer that can be readily infused with silicone oil.[42]

Summary

Introduction

Liquid-infused surfaces (LISs) represent a family of functional surfaces inspired by the Nepenthes pitcher plant whose porous outer surface is imbibed with a lubricating liquid. Regardless of the intended application, all designs of LISs have to meet three main criteria: (1) the chemical affinity between the lubricating fluid and the solid should be higher than that between the ambient fluid and the solid, (2) the solid should preferably be roughened so as to increase the surface area for the adhesion of the lubricating fluid and its immobilization, and (3) the lubricating fluid and the ambient fluid must be largely immiscible.[2,3] Since the initial development of LISs,[2,15−17] many different geometries and materials have been proposed for the porous substructure and lubricating fluid These include the development of flexible surfaces from self-assembling polymers[18] or using novel ferrofluids to infuse surfaces.[19] Experimental advances have further been complemented by theoretical studies to examine ideal geometries and the interplay of the infused liquid with supported liquid droplets moving across the LIS.[20−22]

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