Elsevier

European Polymer Journal

Volume 49, Issue 8, August 2013, Pages 2267-2274
European Polymer Journal

Superhydrophobic surfaces from 3,4-propylenedioxythiophene (ProDOT) derivatives

https://doi.org/10.1016/j.eurpolymj.2013.05.004Get rights and content

Highlights

  • Synthesis and characterization of original fluorinated ProDOT derivatives.

  • Superhydrophobic films with various surface morphologies by electrodeposition.

  • Control of the polymer growth and the surface roughness by changing the used solvent and electrodeposition method.

Abstract

Controlling the polymer growth and the surface morphology in the electrodeposition process is fundamental for applications in liquid-repellent surfaces. We report the synthesis and characterization of original fluorinated (F-butyl, F-hexyl and F-octyl) 3,4-propylenedioxythiophene derivatives as monomers for the elaboration of superhydrophobic and oleophilic surfaces by electropolymerization. The depositions are performed in two solvents (acetonitrile and dichloromethane) and at constant potential. Their surface analyses shows that the lengthening in the fluorinated chain induces a change in the surface morphology from assembly of fibers to quasi-spherical particles. If the presence of spherical particles is better to reach superhydrophobic properties with lower hysteresis and sliding angle, the fibers are much able to repel low surface tension liquids as hexadecane. If the nature of the solvent (acetonitrile or dichloromethane) has not a significant influence on the surface morphology, it can highly affect the surface roughness by favoring a two-dimensional or three-dimensional growth. The growth and the surface morphology can also be controlled by using cyclic voltammetry as deposition method.

Graphical abstract

Superhydrophobic fluorinated poly(3,4-propylenedioxythiophene) films with various surface morphologies can be prepared by electrodeposition and the polymer growth and surface roughness controlled with the used solvent and the electrodeposition method.

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Introduction

Superhydrophobic surface properties are extremely in demand for their various potential applications such as the fabrication of self-cleaning panes [1], the surface protection against corrosion [2], fog [3] and frost [4], for the realization of water-proof textiles [5], clothes protected against dirt as well as hazardous chemicals or biological agents [6]. In the literature, superhydrophobic surface properties are defined by a contact angle made between a water droplet and the surface above 150°. Such surfaces can be obtained by combining surface roughness with low surface energy materials [7], [8]. The general approaches to reach superhydrophobic surfaces include the lithographic processes, the electrospinning, layer-by-layer deposition or sol–gel technologies [9], [10], [11], [12].

The materials used in these methods can be metallic, ceramic or polymeric. Conducting polymers, such as polypyrrole, polythiophene, polyaniline or polyfluorene derivatives can also be used to reach superhydrophobic properties. These materials have unequalled electronic, optic or opto-electronic properties while the production of these polymers as well as the deposition processes are various [13]. For example, aniline is known to form polymer nanofibers by chemical oxidative polymerization in solution using appropriate conditions [14]. From these 1D nanofibers, it was possible to elaborate 3D-microstructures by self-assembly, which could be afterwards deposited on substrates by spin-coating or dip-coating, for example. In this method, the use of perfluorinated salts as dopants allows to modify the geometry of the 3D-structures and also to reach superhydrophobic surface properties [15], [16]. Nanostructured microspheres were also reported by self-assembly of polyaniline nanofibers on polystyrene microspheres [17]. Processes for the growth of polyaniline nanofibers on substrates by chemical oxidative polymerization or grafting were also reported [18], [19], [20].

Whereas self-assembly processes were especially employed with polyaniline, the electrodeposition can be performed with a large variety of conducting polymers. This fast method allows the easy control of the surface morphology and therefore a possible tune of the surface wettability. For example, the surface morphology and roughness are highly depending on the electrochemical conditions (solvent, salt, substrate, deposition charge, electrodeposition method…) and the monomer chemical structure [21], [22]. The strategies are various especially for the introduction of the low surface energy part. If the hydrophobic part can be introduced in a post-treatment [23], most of the papers reported the realization of superhydrophobic surfaces in one-step. Superhydrophobic surface could be realized by electrodeposition of pyrrole or aniline in presence of tetraethylammonium perfluorooctanesulfonate (TEAPFOS) as perfluorinated doping salt [24]. The wettability of these surfaces was switchable with reversible switching between superhydrophobicity and superhydrophilicity by electrochemical reduction/oxidation. Finally, the introduction of the hydrophobic part as substituent of the monomer allowed to reach superhydrophobic surfaces with exceptional anti-wetting properties and stability [22], [25], [26], [27]. Hence, 3,4-ethylenedioxythiophene (EDOT) derivatives were found to be remarkable for their polymerization ability in extremely various electrochemical conditions.

Here, we report the elaboration of water-repellency surfaces by electrodeposition of the original 3,4-propylenedioxythiophene (ProDOT) derivatives, a EDOT derivative with one supplementary methylene unit on the bridge, represented in Scheme 1. These monomers differ by the length of the fluorinated tail (F-butyl, F-hexyl and F-octyl). Previously, we showed, in the case of the electrodeposition of EDOT derivatives containing alkyl chains, that the electropolymerization solvent can allow to reach both structured (in polar solvent such as acetonitrile) and smooth surfaces (in less polar solvent such as dichloromethane) [26a]. Here, the electrodeposition was performed in these two solvents (acetonitrile and dichloromethane). The surfaces, obtained by imposed potential (chronoamperometry), were investigated by static and dynamic contact angle measurements with water, diiodomethane and hexadecane, optical profilometry and scanning electron microscopy in order to determine the effect of the fluorinated chain length and the solvent on the liquid-repellency properties (especially hydrophobicity and oleophobicity).

Section snippets

Synthesis of the monomers

The hydroxylated precursor, (3,4-dihydro-2H-thieno [3,4-b][1,4]dioxepin-3-yl)methanol (ProDOT-OH), was obtained by transetherification of 3,4-dimethoxythiophene with 2-(hydroxymethyl)-propane-1,3-diol in toluene and in presence of a catalytic quantity of p-toluenesulfonic acid (Scheme 2), following a procedure described in the literature [28]. Then, the original monomers (ProDOT-Fn with n = 4, 6 and 8) were obtained by grafting semifluorinated acids to ProDOT-OH via an esterification reaction in

Electrochemistry

As shown in Table 1, the oxidation potentials of the different monomers, presented in Table 1, were higher in dichloromethane than in acetonitrile while the effect of the length of the hydrophobic substituent was not significant. Hence, the ability of electropolymerization was higher in acetonitrile than in dichloromethane. Then, polymer films were electrodeposited by cyclic voltammetry (10 scans) in order to study the growth and the stability of the films. The cyclic voltammograms of the three

Discussion

Looking at the surface roughness and morphology studies, the surface wettability of these fluorinated surfaces could be explained with the Wenzel and the Cassie-Baxter equation, which are usually used to explain the possibility to obtain superhydrophobic properties when the surface is structured [29], [30], [31]. These equations were developed in order to link the wettability to the roughness of the surfaces. Indeed, when a droplet is in the Wenzel state, the water droplet follows the surface

Conclusion

Here, we have shown that fluorinated 3,4-propylenedioxythiophene derivatives can be used as monomer to produce superhydrophobic surfaces with various adhesiveness and oleophobicity by electrodeposition. The surface morphology, from assembly of fibers to quasi-spherical particles, could be controlled with the fluorinated chain length. The fluorinated spherical particles led to superhydrophobic properties with lower hysteresis and sliding angle but the fibers had a higher ability to repel low

Acknowledgments

We thank Jean-Pierre Laugier (CCMA, UNS) for the realization of SEM images. M.W. thanks the PACA (Provence – Alpes – Côte d’Azur) region for a research grant.

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