Wettability alteration from superhydrophobic to superhydrophilic via synthesized stable nano-coating Marzieh Sadat Hosseini, Mohammad Taghi Sadeghi ⁎, Masoud Khazaei Department of Chemical Engineering, Iran University of Science and Technology, Tehran, Iran abstract article info Article history: Received 19 March 2017 Revised 17 June 2017 Accepted in revised form 13 July 2017 Available online 14 July 2017 In this study, synthesized TiO 2 /SiO 2 hybrid nanoparticles were used to fabrication of hydrophilic coating with high stability on superhydrophobic surface of carbonate rock. For this purpose, n-heptane droplet contact angle in water medium was measured on the rock surface before and after treatment. The TiO 2 /SiO 2 nanoparti- cles were synthesized by modified sol-gel method. This method is based on increasing functional groups on the surface of the TiO 2 nanoparticles to produce high hydrophilic nanoparticles. The synthesized nanoparticles were characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The chemical composition and morphology of untreated and treated rock surface were determined using XRD and SEM analyses. It was observed that the n-heptane droplet was instantly spread on the untreated rock and its contact angle in water medium was 0°, in the other hand the water contact angle in n-heptane medium was 168°, so the un-coated rock was superhydrophobic. After adsorption of nanoparticles on the rock surface, the n-heptane droplet contact angle changed to 165° and the water contact angle changed to 0° so the coated rocks were superhydrophilic. The fabricated nano-coatings exhibited high thermal stability and moderate mechanical stability; also the coated surfaces had high stability in contact with salt solution, the results were encouraging. Applications of these nano-coatings include surfaces where cleanliness is paramount such as in hospitals as well as the maintenance of building facades and protection of public monuments from weathering. Novel industrial application includes wettability alteration of oil wet carbonate rock for enhanced oil recovery (EOR). © 2017 Elsevier B.V. All rights reserved. Keywords: Nanoparticles Hydrophobic Hydrophilic Wettability alteration Carbonate rock 1. Introduction Hydrophilic and superhydrophilic surfaces have gained much atten- tion due to their interesting practical applications such as anti-fog coatings [1–3], underwater antifouling surfaces [4], boiling heat transfer [5,6], oil–water separation [7] and fluid flow in porous media such as rocks [8,9]. Modifying the wettability of porous substrates such as rocks is an important subject because of spontaneous imbibition of different liq- uids, water and oil, into porous media. This has many applications, for example, the protection of public monuments and cultural heritage buildings from weathering, as well as the maintenance of facades. Wettability alteration in rock porous media from oil wet to water- wet also has important industrial applications for example in oil pro- duction on which we focused in this study. One of the main challenges in oil production is enhanced oil recovery from oil-wet carbonate reservoir. Many of the world's oil reserves are found in oil-wet carbonate reservoirs [10]. In an oil-wet rock, oil has tendency to stick the rock, Fig. 1(a), due to the hydrophobicity of the walls of porous media, in the other hand in a water wet rock, water has tendency to stick the rock, Fig. 1(b). Water flooding, as a common method for en- hancing oil recovery [11,12], is more efficient in water wet reservoirs than oil-wet ones [13,14]. In water-wet reservoir, mobility of oil in posrous media increases with water injection [15]. In recent years, the construction of hydrophilic and superhydrophilic coatings has been raised, but their use in practical applications has many limitations [16,17] due to the low mechanical and thermal stability of the coated surfaces [18,19]; furthermore in contact with brine solution they may lose their hydrophilicity [20]. Many of these coatings don't have temperature tolerance and destroy at high temperature. Since many of the oil reserves are held in high temperature and salinity reser- voirs, stability of these fabricated coatings should be investigated at these conditions. Some studies have been conducted on wettability alteration of reservoir rocks, based on these researches, the wettability of rocks surface can be altered through the injection of chemicals [21] such as surfactant [22–26] and alkaline/surfactant [27,28]. It is noteworthy that surfactant flooding has very low efficiency [29–31]; also, the Surface & Coatings Technology 326 (2017) 79–86 ⁎ Corresponding author. E-mail address: sadeghi@iust.ac.ir (M.T. Sadeghi). http://dx.doi.org/10.1016/j.surfcoat.2017.07.032 0257-8972/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat