Elsevier

Dyes and Pigments

Volume 130, July 2016, Pages 202-208
Dyes and Pigments

Rapid fabrication of angle-independent structurally colored films with a superhydrophobic property

https://doi.org/10.1016/j.dyepig.2016.03.022Get rights and content

Highlights

  • Non-iridescent structurally colored films were prepared.

  • The films exhibit high contact angles (∼165°) and low roll-off angles (<2°).

  • This method is simple and could be applied on both flat and curved substrates.

Abstract

Structural colors with anti-photo bleaching character have attracted great attentions in energy-saving reflective displaying. However, the brilliant color will disappear once the film is wet, due to the decreased refractive index contrast.

Generally, hydrophobic colored films are produced from hydrophobic nanoparticles, three-dimension ordered macroporous structures or spray coating of hydrophobic treated silica NPs. But the process of the three-dimension ordered macroporous structures is time consuming and this ordered array will lead to iridescent colors. Besides, it has been recognized that some fluorochemicals have potential risks to human health and environment.

In this work, we report the angle-independent structurally colored films with a superhydrophobic property fabricated by spray coating of SiO2 NPs and PDMS. The as-prepared films exhibit a high contact angle (∼165°) and a low roll-off angle (<2°). The combination of non-iridescent structural color and superhydrophobicity is significant for potential applications in outdoors.

Introduction

Chemical pigments used in industries produced from organic or inorganic chemicals are easy to fade over time or upon exposure to light [1], [2], [3], [4]. Recent years, structural colors that originate from interference, diffraction, or scattering of visible light, with the anti-photo bleaching character have attracted great attentions in energy-saving reflective displaying [5], [6], [7], [8], [9], [10], [11], [12], [13]. Commonly observed structural colors could be divided into two classes: one is the iridescent colors from periodic nano- and microstructures, as illustrated in butterfly wings and beetle scales [14], [15], [16]; and another one is the non-iridescent color from amorphous photonic structures (APSs), as illustrated in feathers of many birds which are produced by quasi-random arrays of air vacuoles in the medullary keratin [17], [18].

Non-iridescent structural color is originated from amorphous photonic structures (APSs), in which the interference condition does not vary with orientation, and the color is independent of the viewing angles., non-iridescent structural colors have attracted great attentions in potential applications due to the requirement of broad viewing angle, such as building skins, textiles, display boards, print media, cosmetics, colorimetric sensors, and optical devices [6], [19], [20], [21], [22]. Active research has been conducted on creating angle-independent structural color by packing colloidal crystals into APSs through a variety of approaches such as spin coating, drop-casting, and spray coating [12], [13], [14], [15], [16], [17], [18], [19]. Among them, spray coating offers the benefits of rapid patterning and mass production over a large area on both planar and curved surfaces. Ge et al. prepared a composite film consisting of a thin layer of quasi-amorphous array of silica nanoparticles embedded in bulk elastomeric PDMS [23]. However, the colors emitted from colloidal APSs are very pale since incoherent light scattering across the entire visible region is very strong. To reduce the contribution of multiple-scattered light to the overall scattering spectrum, black component with the character of a high absorption across the entire visible region has been mixed into the spray coating solution [24], [25], [26].

However, the commonly used SiO2 are typically hydrophilic and negatively charged, and brilliant structural colors will disappear once the films are wet due to the decreased refractive index contrast within the films [27]. This disadvantage limits their applications only in a dried environment. Superhydrophobic surfaces with contact angle greater than 150° and slide angle lower than 10° have received great interests within the scientific community as well as the industrial world over the last two decades [28], [29], [30], [31]. Inspired by nature, such as the wings of the Morpho butterfly, a peacock feather and beetle shells, which still maintain brilliant colors even under wet conditions [32]. Thus, it is useful to apply a thin layer of transparent low-surface energy coating on the generated rough surface to prepare superhydrophobic surfaces. [33], [34], [35], Method such as post-treat the colored films with fluoroalkyl silane or alkyl silane were utilized to make superhydrophobic films previously [36], [37], [38], [39]. However, most of them were achieved by vapor deposition under vacuum or by solution casting, in which the post-treatment step is time consuming and may not be desirable for applications in consumer [12]. Tang et al. reported a simple fabrication of colloidal crystal structural color films with good mechanical stability and high hydrophobicity [40]. They also prepared a heat-resistant photonic crystal structural color films fabricated by assembling microspheres of methyl methacrylate (MMA) and methacrylic acid (MAA) through a vertical-lifting process [41]. But the key to superhydrophobic surfaces lies within the combination of surface chemical compositions and topographic structures [28].

Recently, Ge et al. reported superhydrophobic and angle-independent colored films prepared by spray coating of fluorosilane functionalized SiO2 [27]. However, it has been recognized that some fluorochemicals have potential risks to human health and environment [42]. PDMS is a typical elastomeric material with low surface energy of about 20 mN/m has many excellent properties, such as hydrophobicity, low toxicity, long-term endurance, and transparency, make it an attractive material for outdoor applications [43], [44], [45], [46], [47].

There are two general strategies to create superhydrophobic surfaces: (1) introduction of surface roughness or porosity on a low surface energy material, and (2) creation of roughness on surface, followed by deposition of a low surface energy material on top of it. The second approach is simple, low-cost, and versatile.

In this article, we report the structurally colored films with excellent superhydrophobic property by spray coating of monodisperse SiO2 nanospheres and PDMS solution. The fabricating process is very simple and suitable for mass production over a large area on both planar and curved surfaces. Moreover, the stop-bands could be easily tuned by adjusting the size of SiO2 nanospheres. This structurally colored film exhibited a high contact angle (∼165°) and a low roll-off angle (<2°).

Section snippets

Materials

Tetraethoxysilane (TEOS), ethanol, and ammonia (28%) were purchased from Sinopharm Chemical Reagent Co., Ltd of China. Polydimethylsiloxane (PDMS, Sylgard 184 Silicone Elastomer Kit with components of PDMS base and curing agent) was purchased from Dow Corning. Tetrahydrofuran (THF), ethanol (EtOH) was commercially obtained without further purification. Deionized water (18.2 MΩ cm resistivity) was used in all experiments.

Synthesis of SiO2 nanospheres

Monodispersed silica nanoparticles (NPs) were synthesized according to the

Morphology of the structurally colored films

SiO2 is the primary component of soil and found in abundant supply in nature. Which is commonly used to build structurally colored films due to the simplicity in synthesizes and chemically stable. Moreover, in vivo, toxicity of silica particles that are greater than 300 nm in diameter has not been detected [48]. Therefore, submicrometer-sized silica particle become one of the best candidates for fabricating environmental friendly materials. Here, we fabricated the monodisperse silica NPs via a

Conclusions

In summary, superhydrophobic and angle-independent structurally colored films have been prepared by spray-coating of hydrophobic PDMS on SiO2 films. The angle-independent colors could be tuned from blue, green to red by varying the size of the monodispersed silica NPs. And this coating with high water contact angles (167°) and low roll-off angles (<2°) of could effectively prevent the color from fading away when in contact with water. The spray coating method with simple and fast characters

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51472153, 51232008).

References (54)

  • J. Dale et al.

    Intraspecific variation in coloration

    Bird Color

    (2006)
  • S. Kinoshita et al.

    Physics of structural colors

    Rep. Prog. Phys.

    (2008)
  • M. Srinivasarao

    Nano-optics in the biological world: beetles, butterflies, birds, and moths

    Chem. Rev.

    (1999)
  • Y. Takeoka et al.

    Production of colored pigments with amorphous arrays of black and white colloidal particles

    Angew. Chem. Int. Ed.

    (2013)
  • Y. Gotoh et al.

    An amorphous array of poly (N-isopropylacrylamide) brush-coated silica particles for thermally tunable angle-independent photonic band gap materials

    New J. Chem.

    (2012)
  • Y. Takeoka et al.

    Structural colored liquid membrane without angle dependence

    ACS Appl. Mater. Interfaces

    (2009)
  • M. Harun-Ur-Rashid et al.

    Angle-independent structural color in colloidal amorphous arrays

    ChemPhysChem

    (2010)
  • M.G. Han et al.

    Full color tunable photonic crystal from crystalline colloidal arrays with an engineered photonic stop-band

    Adv. Mater.

    (2012)
  • J. Kim et al.

    Real-time optofluidic synthesis of magnetochromatic microspheres for reversible structural color patterning

    Small

    (2011)
  • M. Haque et al.

    Unidirectional alignment of Lamellar bilayer in hydrogel: one-dimensional swelling, anisotropic modulus, and stress/strain tunable structural color

    Adv. Mater.

    (2010)
  • S. Kinoshita et al.

    Structural colors in nature: the role of regularity and irregularity in the structure

    ChemPhysChem

    (2005)
  • P. Vukusic et al.

    Photonic structures in biology

    Nature

    (2003)
  • F. Marlow et al.

    Opale: status und Perspektiven

    Angew. Chem.

    (2009)
  • J.D. Forster et al.

    Biomimetic isotropic nanostructures for structural coloration

    Adv. Mater.

    (2010)
  • Y. Takeoka

    Angle-independent structural coloured amorphous arrays

    J. Mater. Chem.

    (2012)
  • H.C. Gu et al.

    Non-iridescent structural color pigments from liquid marbles

    J. Mater. Chem. C

    (2015)
  • S. Yoshioka et al.

    Production of colourful pigments consisting of amorphous arrays of silica particles

    ChemPhysChem

    (2014)
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