Elsevier

Microelectronic Engineering

Volume 95, July 2012, Pages 130-134
Microelectronic Engineering

Fabrication and characterization of superhydrophobic surface by electroplating regular rough micro-structures of metal nickel

https://doi.org/10.1016/j.mee.2011.12.012Get rights and content

Abstract

The superhydrophobic behavior has attracted many researchers’ attention. The conventional method of obtaining superhydrophobicity involves the combination of the coating of low-surface-energy material and constructing roughness on smooth surface. According to Cassie–Baxter law, this paper proposes a method that the superhydrophobicity could be obtained on structured hydrophilic surface without any coating of low-surface-energy material. Based on the surface micromachining technology, the superhydrophobic behavior has been achieved by the fabrication of micro-nickel cylinder array. It has been proved by the experiments that the micro-cylinder arrays exhibit superhydrophobic behavior; the maximum contact angle (CA) between the array and the water droplet can be up to 155°, while the intrinsic CA of smooth nickel surface is 82°. By controlling the parameters of cylinders (diameter/height/spacing), we investigated the relationship between the hydrophobicity and the above parameters. It proved that the spacing height ratio contributed to the transition from Cassie’s model to Wenzel’s, which was the main cause of disappearance of superhydrophobicity.

Graphical abstract

Based on the surface micromachining technology, the superhydrophobic behavior has been obtained by the fabrication of micro-nickel cylinder array without coating of low-surface-energy material. The prepared micro-cylinder arrays exhibit superhydrophobicity with the maximum contact angle (CA) of 155°, while the intrinsic CA of smooth nickel surface is 82°. By controlling the parameters of cylinders (diameter/height/spacing), the relation between the hydrophobicity and the above parameters were investigated. It proved that the spacing height ratio contributed to the transition from Cassie’s model to Wenzel’s, which was the main cause of disappearance of superhydrophobicity.

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Introduction

Superhydrophobic surface, on which the water droplet beads up with a contact angle larger than 150°, have many applications in electrical and mechanical industry [1]. Basically, it follows two rules to obtain the superhydrophobicity, either by enhancing surface roughness or by coating of low surface energy materials [2]. It has been shown that with the combination of constructing rough surface structures and low energy material coating, super-hydrophobic surfaces could be easily prepared [3], [4], [5], [6], [7], [8], [9]. Many processes have been proposed to fabricate super-hydrophobic surface: such as micro-pattern, template, nanostructure manufacturing, super-hydrophobic coating [10], [11], [12]. The electrical, chemical, mechanical characters of these surfaces have also been discussed. Superhydrophobic phenomenon could be classically explained by two distinct hypotheses, the Wenzel and Cassie models. In the Wenzel model [13] the liquid completely fills the cavity of rough surface, while in the Cassie’ case [14] air is trapped underneath the liquid, which result in a composite surface. Although the validity and feasibility of the two models have been argued in recent years [15], [16], the models play key roles in guiding the design of superhydrophobic surfaces. There are many ways to make rough surfaces such as mechanical stretching, laser/plasma/chemical etching [17], [18], lithography [19], sol–gel processing and self-assembly [20], layer-by-layer and colloidal assembly [21]. It had been reported that the hydrophobic silicon surface was obtained with coating of OTS (octadecyltrichlorosilane) by the ICP (Inductively Coupled Plasma) etching on hydrophilic silicon surface [22].

The superhydrophobicity was obtained by the coating of low surface material on structured surfaces. However, it was notable that the adhesion force between the coated hydrophobic membrane and substrate was weak, and the coated membrane were generally electrically insulated. These flaws have confined the application of the superhydrophobic surfaces. In this paper, we proposed an alternative way based on the surface micromachining technology. The nickel array consisted of micro cylinders on copper film was manufactured. It proved that without coating of low-surface-energy material like OTS, the array exhibited superhydrophobicity. The relationship between the parameters of microarray and hydrophobicity was investigated. And mechanism of the transition from Cassie’s model to Wenzel’s model was also discussed.

Section snippets

Basic concept

A droplet would have a shape of spherical cap when it dipped on the surface, a curvature profile was obtained and then the contact angle measured. The CA between droplet and smooth surface was called the intrinsic CA. And the CA between the droplet and rough surface was named the apparent CA. The relationship between the intrinsic and apparent CA was described by two different theories, Wenzel [13] law and Cassie [14] law.

In the Wenzel’s case, the water fills the gaps of rough surface

Micro-fabrication

Surface micromachining technology was widely applied in the manufacturing of MEMS devices [22], [23], [24], [25], [26]. In this paper, we fabricate microarray by metal-based surface micromachining technology. The fabrication process was illustrated in the Fig. 2. Copper/chrome was sputtered on the quartz substrate, followed by the photo-resist spin-coat (Fig. 2a and b). After photolithography process, the photo-resist pattern was formed. Next, electroforming was conducted by using nickel

Results and discussion

Fig. 3 shows the SEM images of prepared microarrays and their apparent CAs. With the help of transilluminator, the transmitted light could be observed between the droplet and the surface, which showed the air was trapped under the droplet, so the Cassie’s law was suitable in this experiment.

Eq. (2) suggested that the air was the key factor that contributed to the hydrophobicity. Available air that trapped among the cylinders formed a curtain at the cylinder–water interface, which prevented the

Conclusion

In this paper, the microarrays consisted of nickel cylinders were fabricated by surface micromachining technology. It proved that hydrophobicity could be obtained by constructing regular rough structure on hydrophilic surface. Without any coating of low-surface-energy material on the fabricated microarray, the maximum contact angle was up to 155°. The super-hydrophobicity was tuned by changing the parameters of cylinders, such as the diameter d, space size a and height H. Based on Cassie’s

References (31)

  • H. Zhang

    Sci. Technol. Adv. Mater.

    (2005)
  • L.M. Lacroix

    Surf. Sci.

    (2005)
  • H. Shang

    Thin Solid Films

    (2005)
  • Y.H. Zhang

    Mechatronics

    (2007)
  • Z. Xi

    J. Mater. Chem.

    (2008)
  • H. Tao

    Appl. Surf. Sci.

    (2010)
  • X. Feng et al.

    Adv. Mater.

    (2006)
  • H. Zhang

    Appl. Phys. Lett.

    (2007)
  • J.M. Xi

    Appl. Phys. Lett.

    (2008)
  • C. Dorrer et al.

    Adv. Mater.

    (2009)
  • T. Nakanishi

    Adv. Mater.

    (2008)
  • A. Lafuma et al.

    Nat. Mater.

    (2003)
  • D. Quéré

    Rep. Prog. Phys.

    (2005)
  • Y. Zhang

    J. Mater. Chem.

    (2008)
  • J. Pacifico

    Langmuir

    (2006)
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    The project was supported by the Nano Special Program of Science and Technology Commission of Shanghai Municipality, under the Grant No. 1052nm02200 and The Program of Science and Technology Commission of Shanghai Municipality under the Grant No. 11DZ2290203.

    1

    These authors contributed equally to this work.

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