Article pubs.acs.org/Langmuir
Clay and DOPA Containing Polyelectrolyte Multilayer Film for Imparting Anticorrosion Properties to Galvanized Steel Emilie Faure,† Emilie Halusiak,† Fabrice Farina,‡ Nicoletta Giamblanco,§ Cécile Motte,∥ Mireille Poelman,∥ Catherine Archambeau,‡ Cécile Van De Weerdt,⊥ Joseph Martial,⊥ Christine Jérôme,† Anne-Sophie Duwez,§ and Christophe Detrembleur*,† †
Center for Education and Research on Macromolecules (CERM), University of Liège, Sart-Tilman, B6, B-4000 Liège, Belgium CRM Group, AC&CS, Bld de Colonster B57, B-4000 Liège, Belgium § Nanochemistry and Molecular Systems (NANOCHEM), University of Liège, Sart-Tilman, B6, B-4000 Liège, Belgium ∥ Materia Nova asbl, Avenue Copernic, B-7000 Mons, Belgium ⊥ Laboratory of Molecular Biology and Genetic Engineering, GIGA-R, University of Liège, Sart-Tilman, B34, B-4000 Liège, Belgium ‡
S Supporting Information *
ABSTRACT: A facile and green approach is developed to impart remarkable protection against corrosion to galvanized steel. A protecting multilayer film is formed by alternating the deposition of a polycation bearing catechol groups, used as corrosion inhibitors, with clay that induces barrier properties. This coating does not affect the esthetical aspect of the surface and does not release any toxic molecules in the environment.
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INTRODUCTION Because galvanized steel (GI) is rather sensitive to humidity and oxygen, chromium based coatings have been widely used to deal with the white rust formation. Until now, chromate solutions have been the most effective inorganic inhibitors.1 However, this product is well-known to be toxic and carcinogenic and is now prohibited on end products and highly regulated on industrial lines by European Community directives (VUH and RoHS). Therefore, there has been an extensive search for green and human safe anticorrosion treatments. These smart coatings must be able to deal with local pH changes in the corrosive area but also be able to prevent interactions of corrosive species (water, chlorine ions, oxygen, ...) with the metal surface. Many strategies have been implemented for that purpose, such as by building polyelectrolytes multilayer films,2 strongly anchoring a protecting polymer by electropolymerization,3 incorporating active nanocontainers for self-healing,4 or using corrosion inhibitors5 or natural polymers/molecules with intrinsic anticorrosion properties.6 However, these systems are most often specific to their substrates (mild steel, stainless steel, aluminum, ...) and so are not suitable for galvanized steel (Table S1, entries 2 and 3, ESI†). Ultrathin plasma inorganic films of SiOx are reported to present interesting barrier properties on GI7 and can be combined with cerium nanoparticles to impart self-healing properties.8 Silane layers generally show rather good barrier properties,9 but used alone, silanes are not able to provide self-healing to the metal. Many © 2011 American Chemical Society
researches are thus dealing with the combination of silanes with inhibitors (cerium, ...)10 or inhibitors nanocontainers,9c,11 the main drawback of this approach being the difficult step of particles incorporation into the silane matrix. Very recently, a waterborne polyurethane solution containing various inorganic inhibitors (titanates for instance) was successfully implemented for that purpose.12 In this paper, we report on a novel and green approach to provide anticorrosion properties to galvanized steel by codepositing clays with a water-soluble copolymer grafted by nature inspired antioxidant groups, i.e. catechols. Our strategy is based on the innovative combination of two permanently charged partners, alternatively deposited on the surface by the LbL technology.13 The first one is a tailored copolymer of a methacrylamide bearing 3,4-dihydroxyphenylalanine (mDOPA) groups and [2-(methacryloxy)ethyl] trimethylammonium chloride (DMAEMA+). It thus consists in the positive organic part of our multilayer, named P(mDOPA)-coP(DMAEMA+) (Scheme 1a).14 The second partner is a small colloidal synthetic and commercial layered silicate, Laponite S482, modified by pyrophosphates. This modified clay is negatively charged and is highly soluble in water (up to 250 g/ L) with the formation of stable dispersions of clay platelets with a diameter of about 25 nm and a thickness of 1 nm.15 Laponite Received: November 8, 2011 Revised: December 26, 2011 Published: December 26, 2011 2971
dx.doi.org/10.1021/la204385f | Langmuir 2012, 28, 2971−2978
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electron microscope (FEG-SEM) MEB ULTRA55 operating at 3 kV was used for sample observation after a thin layer (10 nm) of Au−Pd to increase the contrast. The XPS analyses were performed in a PHIQuantum 2000 spectrometer. The spectrometer is characterized by a monochromatized Al Kα primary X-ray beam and a photoelectron takeoff angle of 45° against the sample normal direction. Charge effects were compensated with low energy electrons. AFM experiments were carried out with a PicoPlus (Agilent Technologies). Images were obtained in the intermittent contact mode with PointProbe-Plus Silicon cantilevers (Nanosensors, nominal resonance frequency of 330 kHz, force constant of 42 N m−1, and tip radius
