Robust Superhydrophobic Surface on Polypropylene with Thick Hydrophobic Silica Nanoparticle-Coated Films Prepared by Facile Compression Molding

Oyunchimeg Erdene-Ochir,Doo-Man Chun

doi:10.3390/en14113155

Abstract

Superhydrophobic surfaces have been extensively studied for their unique interfacial interaction between water and the surface, and they can be used for self-cleaning, drag reduction, anti-icing, and other applications. To make the superhydrophobic surfaces, nano/microscale structures and a low surface energy should be realized. The development of a durable superhydrophobic surface was hindered by the vulnerability of the surface to mechanical contact. To improve the robustness of the superhydrophobic surface toward mechanical damage, the hydrophobic polypropylene (PP) surface was coated with a thick layer of hydrophobic silica nanoparticles (SNPs) using a simple compression molding process. The thick layer consists of SNPs and PP, and the roles of SNPs and PP are nano/microscale structures with a low surface energy and binder for nanoparticles, respectively. This revealed improvement in the superhydrophobic tendency, with an apparent contact angle of about 170° and a sliding angle of less than 5°. The morphology and the corresponding elemental analysis of the PP/SNPs coated films were investigated using field emission scanning electron microscopy and energy-dispersive spectrometry. The mechanical durability of the superhydrophobic surface was evaluated by the scotch tape test and scratch test with sandpaper. The coated films with SNPs showed the superhydrophobic behavior after 25 tape tests. In addition, the coated films with SNPs showed a contact angle greater than 150° and a sliding angle less than 10° after a 100-cm scratch test with 1000 grit sandpaper, under a weight of 500 g, on an area of 40 × 40 mm2. The chemical stability of PP/SNPs coated films was also investigated in acidic, neutral, and alkaline medium solutions. The films showed good stability under the acidic and neutral medium solutions even after 24 h, but an alkaline medium could damage the surface. The obtained results demonstrated the robustness of the superhydrophobic coating with SNPs.

Highlights

Superhydrophobic surfaces have been extensively studied for their unique interfacial interaction between water and solid surface, and the superhydrophobic surface was defined by a water contact angle (CA) greater than 150◦, and sliding angle (SA) less than 10◦ [1,2] with numerous special properties, such as self-cleaning [3,4,5], anti-icing [2,6], water-proofing [7] and anti-fouling [4,5,7]
We developed a simple compression molding process for the fabrication of superhydrophobic PP/silica nanoparticles (SNPs) coated films
The scotch tape test and scratch test were used to check the mechanical durability of our fabricated PP/SNPs coated films

Summary

Introduction

Superhydrophobic surfaces have been extensively studied for their unique interfacial interaction between water and solid surface, and the superhydrophobic surface was defined by a water contact angle (CA) greater than 150◦ , and sliding angle (SA) less than 10◦ [1,2] with numerous special properties, such as self-cleaning [3,4,5], anti-icing [2,6], water-proofing [7] and anti-fouling [4,5,7] These properties may come from the minimum contact area of the water–solid interface as well as the trapped air at the interface, and they can control the material and energy transport at the interface. Since 1995, many researchers have reported many creative ways to make rough surfaces with low surface energy

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