Elsevier

Applied Surface Science

Volume 367, 30 March 2016, Pages 432-437
Applied Surface Science

Stable and conformable superhydrophilic surface fabricated via surface-initiated silicification on polyaniline nanofibers

https://doi.org/10.1016/j.apsusc.2016.01.215Get rights and content

Highlights

  • A method to fabricate stable and conformable superhydrophilic surfaces is proposed.

  • The resulting surface showed enhanced wettability and stable superhydrophilicity.

  • Conformable superhydrophobic–superhydrophilic patterned surfaces can be realized.

Abstract

Superhydrophilic surfaces have attracted much interest owing to their great potential for practical applications. Conventional methods for fabricating superhydrophilic surfaces result in unstable wetting properties and less conformability with respect to a target object. Here, we report an integrative method that improves the stability of surface wettability and extends adaptability to various materials and shape structures through the direct growth of a silica layer on polyaniline nanofibers. The wetting behavior of the fabricate surface was greatly enhanced by our fabrication method, and the modified surface maintained superhydrophilicity for more than 2 months. Taking advantage of the adhesive property of polyaniline, we further realized a conformable superhydrophobic–superhydrophilic patterned surface by photopatterning a hydrophobic alkylthiol coating on the polyaniline surface. The proposed method is expected to open up various applications, particularly in water harvesting.

Introduction

Superhydrophilic surfaces, which are generally characterized by a very low water contact angle (CA) less than 10° and quick water-spreading property, have been attracting increased interest because these surfaces open up practical applications such as anti-fogging surfaces [1], bio-fouling devices [2], and the enhancement of heat transfer [3]. Recently, a number of methods have been introduced to achieve the wetting behavior by texturing surfaces based on Wenzel's model or chemically modifying the surfaces with materials having high surface free energy. These methods include the fabrication of alumina nanowire structures by anodization [4], hierarchical structures by chemical etching [5], TiO2 photocatalyst coatings based on the photocatalytic oxidation activity of the material [6]. However, methods based on anodization and etching can cause damage on the surface and are strongly dependent on the substrate materials. The coating method using photochemically active materials has been studied by many researchers, but the coated surfaces are unstable and easily lose their superhydrophilicity in the absence of UV irradiation [7].

Polyaniline (PANI), one of the attractive conducting polymers, has great potential for application in various industrial fields owing to its high conductivity, inexpensive preparation, and good chemical stability. PANI can also exist in various forms having different oxidation states, including emeraldine salt (ES), emeraldine base (EB), pernigraniline base (PB), and leucoemeraldine base (LEB), and the form can be easily adjusted through a doping–dedoping process or redox reaction, as shown in Fig. 1 [8], [9]. These characteristics of PANI allow extensive applications in chemical sensing devices [10], energy storage devices [11], and filtration [12]. Moreover, PANI can grow and form micro/nano structures on various substrates, regardless of their shape and composition; hence, it has been widely used to modify surface wettability. For instance, superhydrophilic nanofiber-structured PANI surfaces were fabricated on conductive electrodes through electrochemical deposition in an electrolyte containing aniline monomer [13], [14]. A facile spray-coating method was used to produce a superhydrophobic surface using PANI particles doped with a low-surface-energy material, and it was found that the wettability of the surface could be switched between superhydrophobicity and superhydrophilicity according to the doping and dedoping state of PANI [15]. However, the electrochemical deposition methods are limited to conductive materials and cannot be readily adapted to complex shape structures. Furthermore, the sprayed surface may be easily delaminated owing to low adhesion between the deposited hydrophobic PANI particles and an underlying substance. More importantly, the wettability of the PANI deposited on the surfaces may be easily decreased owing to the loss of the doping ions closely related to the wettability. Therefore, it is necessary to develop a new method that would result in a superhydrophilic surface that is easily applicable on various substrates and is environmentally stable for long-term use without the degradation of wettability.

In this paper, we report the fabrication of superhydrophilic surfaces that can be readily fabricated from PANI nanofiber structures and the growth of a silica layer by subsequent surface-initiated silicification. The silica layer on PANI might be suitable for stable superhydrophilic surfaces because the wettability of the fabricated surface cannot be affected by the influences of doping ions and oxidation states of PANI. Owing to the intrinsic adherent nature of PANI, the proposed method would also be an effective approach for producing conformable superhydrophilic surfaces on flexible polymer substrates. In addition, combined with a hydrophobic coating and UV photopatterning, a superhydrophobic–superhydrophilic patterned surface that is easily adaptable to 3D structures can be successfully fabricated. These advances would enable us to develop functional surfaces for water condensation and transportation.

Section snippets

Experimental

PANI nanofibers were synthesized on a polyolefin (PO) heat-shrinkable film (thickness: 550 μm, Korea Ace Tech. Co., Ltd., Korea) through the dilute polymerization method [16], [17], [18]. In comparison with other methods to deposit PANI film such as plasma polymerization [19] and matrix assisted pulsed lased evaporation (MAPLE) [20], the dilute polymerization is a simple and inexpensive method to fabricate uniform nanofiber structures without using expensive devices and complicate processes. And

Results and discussion

The fabrication process of a stable superhydrophilic surface involving the growth of PANI nanofiber structures and a silica coating on the structure is schematically shown in Fig. 2. A PO film is immersed in a perchloric acid (HClO4) solution containing aniline to grow PANI nanofiber structures via chemical polymerization. The acid is prone to the protonate amine of PANI, which leads to positively charged nitrogen. To maintain the neutrality of charge, negatively charged acid ions such as ClO4

Conclusions

In this article, we have successfully developed an excellent superhydrophilic surface based on a formation of a stable hydrophilic ceramic layer on unstable hydrophilic PANI nanofibers. The thin ceramic layer was achieved by utilizing a surface-initiated silicification reaction triggered by tertiary amine-containing self-assembled monolayer on the PANI surface. Unlike the wettability of a normal PANI surface which is affected by doping ions and the oxidation states of PANI, silicificated PANI

Acknowledgments

This work was supported by a grant from the National Research Foundation (NRF) of Korea (No.2013R1A2A1A01016911), which is funded by the Ministry of Science, ICT and Future Planning, Korea.

References (37)

  • R. Wang et al.

    Light-induced amphiphilic surfaces

    Nature

    (1997)
  • S. Gao et al.

    Superhydrophilicity of highly textured carbon films in range of pH Values from 0 through 14

    J. Phys. Chem. C

    (2010)
  • J.A. Smith et al.

    Gold–polyaniline composite Part I. Moving electrochemical interface

    Phys. Chem. Chem. Phys.

    (2005)
  • P. Xu et al.

    Multifunctional polymer-metal nanocomposites via direct chemical reduction by conjugated polymers

    Chem. Soc. Rev.

    (2014)
  • D.K. Bandgar et al.

    Simple and low-temperature polyaniline-based flexible ammonia sensor: a step towards laboratory synthesis to economical device design

    J. Mater. Chem. C

    (2015)
  • M.-H. Bai et al.

    Electrodeposition of vanadium oxide-polyaniline composite nanowire electrodes for high energy density supercapacitors

    J. Mater. Chem. A

    (2014)
  • Y. Liao et al.

    Carbon nanotube-templated polyaniline nanofibers: synthesis, flash welding and ultrafiltration membranes

    Nanoscale

    (2013)
  • H. Zhang et al.

    Preparation of nanostructured polyaniline and its super-amphiphilic behavior

    Macromol. Rapid Commun.

    (2008)
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