Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat Extended protection of mild steel in saline and acidic environment using stearic acid grafted chitosan preloaded with mesoporous-hydrophobic silica (mhSiO 2 ) K.O. Shamsheera, Anupama R. Prasad, Abraham Joseph ⁎ Department of Chemistry, University of Calicut, Calicut University P O, Kerala, India ARTICLEINFO Keywords: Chitosan Mesoporous SiO 2 PDP Impedance spectroscopy FESEM AFM ABSTRACT This study produces an enhanced anti-corrosion property of chitosan-based flm on mild steel (MS) in diferent aggressive media using surface modifed SiO 2 . Mesoporous hydrophilic SiO 2 is rendered hydrophobic by using silylating agent hexamethyl disilazane (HMDS). The incorporation of 3.0 weight percentage surface-modifed silica into the chitosan matrix and further grafting with stearic acid (SA) through 1-ethyl-3-(3-dimethylamino- propyl) carbodiimide (EDC) mediated coupling reaction improve the anti-corrosion properties of the coating on mild steel. The resulting chitosan-based flm was characterized by FTIR, TGA, AFM, FESEM, and EDX techniques. The flm formed was applied for corrosion protection of mild steel in 0.5 M HCl and 3.5% NaCl and analyzed via non-electrochemical and electrochemical techniques. 1. Introduction Mild steel is one of the most common and important industrial raw materials of daily life. Iron is sensitive to various aggressive environ- ments like oxygen, water, and humidity. Consequently, bare steel cor- rodes very easily and the corrosion processes afect the mechanical properties [1,2]. One way to protect mild steel is by the application of the coatings. Among the strategies of corrosion protection, the chro- mate conversion coating is proved to be environmentally unfriendly. Several carbohydrate polymers and their composite are being used to develop anticorrosive coating on diferent metal atoms. Chitosan (C) is a promising material for coating applications because of its flm- forming properties, non-toxicity, low cost, chelation by metals, and chemical functional fnishing [3,4]. In our previous report, SA grafted chitosan flm (CSA) contributes desirable corrosion protection for MS in 0.5 M HCl and 3.5% NaCl [5,6]. CSA acted as an efective barrier in NaCl medium when it was blended with epoxy resin. We have used electrochemical and weight loss technique to ensure the corrosion protection efciency of CSA. We could see the protection efciency of about 82% after 20 days of immersion when it was exposed to 3.5% NaCl and 0.5 M HCl. According to literature, the incorporation of metal oxide nanoparticles can enhance the durability of the polymer coatings and provide extra protection efciency by forming a dense barrier against the difusion of aggressive ions [7–9]. Ruhi et al. incorporated chitosan-polypyrrol-SiO 2 composite into the epoxy coating and coated on mild steel using powder coating technique. Corrosion monitoring was carried out via salt spray test, Electrochemical impedance spec- troscopy, and potentiodynamic polarization studies. The composite ofered a protection efciency of about 97% after 60 days of immersion [10]. Fayyad et al. used graphene oxide as nanofller into the chitosan oleate matrix and the corrosion study was monitored using electro- chemical impedance spectroscopy and potentiodynamic polarization studies and ofered efective protection of carbon steel in 3.5% NaCl solution [11]. John et al. developed nanostructured chitosan/ZnO flm on mild steel by sol-gel process and monitored anticorrosion perfor- mance via EIS and potentiodynamic polarization studies [7]. Because of the surface hydroxyl groups of SiO 2 in the form of isolated, geminal, and vicinal silanol it is unft as a fller in the chitosan matrix. Therefore, to enhance the compatibility between the chitosan matrix and silica material, the hydrophilic surface of silica needs to be modifed to hy- drophobic [12–14]. Herein we silylated SiO 2 surface via HMDS, as it can scavenge the –OH group by inert methyl siloxy group [15,16]. This research investigates the infuence of diferent loadings of hydrophobic silica nanoparticles on the anticorrosion performance of chitosan polymer matrix and SA grafted chitosan. 2. Materials used for the study The Chitosan oligosaccharide with a degree of deacetylation of 85% was obtained from Sigma Aldrich. Stearic acid (SA), 1-ethyl-3-(3- https://doi.org/10.1016/j.surfcoat.2020.126350 Received 18 July 2020; Received in revised form 16 August 2020; Accepted 24 August 2020 ⁎ Corresponding author. E-mail address: abrahamjoseph@uoc.ac.in (A. Joseph). Surface & Coatings Technology 402 (2020) 126350 Available online 25 August 2020 0257-8972/ © 2020 Elsevier B.V. All rights reserved. T