Progress in Organic Coatings 105 (2017) 291–302 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur na l ho me pa ge: www.elsevier.com/locate/porgcoat Epoxy embedded with TiO 2 nanogel composites as promising self-healing organic coatings of steel Ayman M. Atta a,b,∗ , Hamad A. Al-Lohedan a , Ashraf M. El-saeed b , Hussin I. Al-Shafey b , Mohamed H. Wahby a a Surfactant Research Chair, Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia b Petroleum Application Department, Egyptian Petroleum Research Institute, Nasr City 11727, Cairo, Egypt a r t i c l e i n f o Article history: Received 19 October 2016 Received in revised form 20 November 2016 Accepted 12 January 2017 Keywords: Titanium dioxide Nanogel Composites Epoxy Salt spray Corrosion Coatings a b s t r a c t Nanomaterials attracted great attention to improve the fracture resistance and to solve the crack initi- ation and crack propagation of epoxy resin problems. In this work, modification of TiO 2 surfaces with crosslinked smart nanogel is proposed technique to improve the mechanical properties of epoxy coat. N-Isopropyl acrylamide (NIPAm) was selected as smart monomer to prepare crosslinked copolymers with acrylic acid (AA) or acrylamide (AAm) using dispersion radical polymerization. The chemical struc- ture, thermal stability, morphology, particle size and surface charges of TiO 2 nanogel composites were determined to investigate the dispersability of nanogel in epoxy resin. The effect of TiO 2 nanogel composites on the mechanical properties and corrosion resistivity of epoxy resins as organic coatings for steel were investigated and discussed. It is shown that the incorporation of TiO 2 nanogel composites based on NIPAm/AA and AA/AAm nanogels into epoxy matrix can improve the self-healing characteristics of damaged epoxy composites even at low contents. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Epoxy resins as thermosetting materials have been widely used as organic coatings for different metallic substrates as well as electronic devices although they are extremely brittle, toughness, beside presence of micro cracks at their surfaces [1]. Different materials have been used to treat these problems by using flexi- ble materials as an intermediary phase either with blending or by chemical reactions. These materials are based on four types and classified as: thermoplastic terminated with reactive functional groups, reactive liquid rubbers, and inorganic polymer compos- ite and reactive ductile diluents. The selection of these materials depends on their efficiency to treat the problem without affect other mechanical properties and these materials possess significant improvement of physical and chemical properties. The nanomate- rials based on nanocomposites attracted great attention as superior additives more than those of the bulk materials [2]. It was reported that, different types of nanoparticles have been used to improve the toughness problem of cured epoxy resins such as titania, clay, silica, ∗ Corresponding author at: Surfactant Research Chair, Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia. E-mail address: aatta@ksu.edu.sa (A.M. Atta). alumina and carbon black [3–8]. These nanomaterials can be mod- ified with organic polymers to prepare superior nanocomposite materials to improve both mechanical properties and self-healing of deformed epoxy coats [9–12]. The nanomaterials can act as nanocapsules to release smart materials to repair the damages of coats and as corrosion inhibitors for different substrates [13–15]. The nanogel porous composites achieved good results as smart nanomaterials to form thin films at surfaces of substrates [16–20]. The size and dispersion of nanomaterials in epoxy resins are big challenges to apply these materials to improve physicochemical properties of epoxy coats. For this reason, both TiO 2 and poly- mer nanogel composites attracted researchers attention because both materials have superior properties useful in their coat applica- tions [21–23]. It was reported that the presence TiO 2 nanocontainer contains organic corrosion inhibitors such as 8-hydroxyquinoline, polyaniline, and polyethylenimine in the epoxy matrix suggesting a possible self-healing effect [24–26]. However, because of their aggregation due to incompatibility of TiO 2 with organic epoxy coat- ings, it was necessary to modify their surfaces to be highly dispersed in epoxy matrix using amphiphilic materials [27,28]. In our previ- ous work, the surface properties of TiO 2 with amphiphilic nanogels increased their dispersion in aqueous and non-aqueous solutions and achieved high corrosion inhibition at lower concentrations [29,30]. In the current study, the surfaces of TiO 2 nanoparticles http://dx.doi.org/10.1016/j.porgcoat.2017.01.009 0300-9440/© 2017 Elsevier B.V. All rights reserved.