Elsevier

Applied Surface Science

Volume 254, Issue 6, 15 January 2008, Pages 1593-1598
Applied Surface Science

Facile method to prepare lotus-leaf-like super-hydrophobic poly(vinyl chloride) film

https://doi.org/10.1016/j.apsusc.2007.07.140Get rights and content

Abstract

A simple new approach was developed to obtain a super-hydrophobic PVC film from a natural lotus leaf using the nanocasting method. SEM shows that compared with a common smooth PVC film, a lotus-leaf-like surface structure was clearly observed on the super-hydrophobic PVC film. The water contact angle and rolling-off angle on the as-prepared lotus-leaf-like PVC film were 157 ± 1.8° and 3 ± 0.6°, respectively. The samples were kept at temperatures between 5 and 40 °C in the ambient atmosphere for 2 months, and no decrease in water contact angle was observed, nor was contamination observed.

Introduction

Wettability is an important property governed by both the chemical compositions and the geometrical structures of solid surfaces. A surface having a water contact angle greater than 150° is commonly called super-hydrophobic [1]. Super-hydrophobic surfaces have attracted much attention due to their great potential applications in agriculture and industry. Recently, many works focused on the super-hydrophobic surfaces have been carried out [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], such as super-hydrophobic fluorocarbon coating with ribbon surface structures [9], super-hydrophobic silica aerogels [10], chemical vapor deposition of trimethylmethoxysilane [11], super-hydrophobic surface based on a steric acid self-assembled monolayer over polyethyleneimine thin films [13], super-hydrophobic carbon films in a wide range of pH values [18], super-hydrophobic zinc oxide thin films after modification with fluoroalkyl silane [20], and honeycomb-like aligned carbon nanotube films [21]. Most of these super-hydrophobic surfaces were prepared by either functionalizing the precursor materials with low-surface-energy groups such as fluorinate, silicon and fluoroalkyl silane [15], [16], [17], [18], [20], [21] or using some expensive materials such as carbon nanotubes [9], [10], [11], [14], [19]. Thus, preparing a super-hydrophobic surface from a common hydrophobic material without addition of low-surface-energy compounds is commercially important and scientifically challenging. Although some progresses have been reported [22], [24], [25], the preparation procedures were either complicated or carried out at fairly high temperatures. In addition, most of the synthesized surfaces became unstable over time in humid environments and exhibited a gradual loss of hydrophobicity.

Nanocasting, which is based on soft lithography [27], [28], is a method used widely in nanofabrication. By directly replicating the template to create larger uniform patterns, the cost of larger-scale fabrication is reduced [29]. In this method, a kind of soft and deformable material is used to cast and replicate the structures of the template surfaces. After this soft material solidifies, the complement of the surface structures on the original template is transferred to the solidified material. This new template can be used to replicate the surface structures or patterns repeatedly as long as the template is not destroyed factitiously. Herein, we present a super-hydrophobic PVC surface prepared using the nanocasting method from a natural lotus leaf. The as-prepared PVC surface shows similar surface structure and water-repellent behavior to the natural lotus leaf. To our knowledge, this is the first report of creating a super-hydrophobic PVC surface using a natural lotus leaf as template and replicating it. It should be noted that the super-hydrophobicity of the as-prepared PVC film is stable in the ambient atmosphere.

Section snippets

Experimental

The schematic diagram of the preparation of the lotus-leaf-like PVC film is shown in Fig. 1. In the preparation, a mould was used to control the size of the PDMS template (shown in Fig. 1). First, the four baffles were fixed on the substrate to form a mould with a height of 3 cm, and the inner length and width of the mould were 15 and 10 cm, respectively. A fresh natural lotus leaf with the length 15 cm and width 10 cm was placed carefully on the bottom of the mould, and then we cast the mixture of

Results and discussion

The SEM image of the natural fresh lotus leaf is shown in Fig. 2a and b is the higher magnification SEM image of the lotus leaf. From Fig. 2a and b, we can find many small papillary hills on the natural lotus leaf. The diameters of the small papillary hills are between 5 and 10 μm. The AFM images (shown in Fig. 3a and b) show that the top surfaces of the papillary hills on the natural fresh lotus leaf are comprised of nanostructures, indicating the top surface of the papillae is rough. Fig. 2c

Conclusions

A stable super-hydrophobic PVC film with a similar surface structure to the natural lotus leaf has been prepared by nanocasting method. The water contact angle and rolling-off angle of the as-prepared lotus-leaf-like PVC film were 157 ± 1.8° and 3 ± 0.6°, respectively. Compared with other methods to prepare lotus-leaf-like surfaces, the presented method, using a natural lotus leaf as template and replicating it directly by nanocasting, is much simpler to control, without any complicated processes

Acknowledgements

The authors are grateful for helpful discussion from Miss Kangli Yang. The authors would like to thank the help of Dr. Xueen Jia and Prof. Jiqing Xie (Hunan Normal University) for the atomic force measurements.

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