Organization of SiO 2 and TiO 2 Nanoparticles into Fractal Patterns on Glass Surface for the Generation of Superhydrophilicity Nainsi Saxena, Tapaswinee Naik, and Santanu Paria* Interfaces and Nanomaterials Laboratory, Department of Chemical Engineering, National Institute of Technology, Rourkela 769008, Orissa India * S Supporting Information ABSTRACT: The superhydrophilic surfaces have many important practical applications such as antifogging, antifoul- ing, self-cleaning, etc. The present study demonstrates a simple and facile template-assisted dip-coating approach for the organization of silica (SiO 2 ) and titania (TiO 2 ) nanoparticles (NPs) into fractal patterns on the glass surface. The pure NPs suspension showed a “coffee ring effect” and did not form any organized pattern on the glass surface after drying. In this reported method, NPs were organized into fractal patterns using a template consisting of sodium carboxymethyl cellulose (CMCNa) and oxalic acid mixture in the presence of a cationic surfactant (CTAB). The presence of surfactant plays a major role to alter the coffee ring effect because of a Marangoni flow in the direction of droplet edge to its center induced by the surface tension gradient and surface potential of the particles, which eventually helps to get a uniform fractal pattern. Finally, the fractal patterns of only SiO 2 and TiO 2 NPs were attained on the glass surface after calcining the CMCNa template at 450 °C. The obtained fractal patterns of SiO 2 and TiO 2 coated glass surfaces showed the average water contact angle of ∼6° and ∼8° respectively, whereas coating of only NPs without pattern could not achieved such low average contact angle. These coated surfaces were found to have an excellent antifogging property (transparency of the surface) in the presence of water vapor. 1. INTRODUCTION The wettability of the solid surfaces is an attractive and emerging research field of study in recent years because of its many advanced practical applications and academic inter- ests. 1-5 The term superhydrophilicity refers to the strong affinity of water toward any surface with water droplet contact angle (θ) < 10°, in contrast, superhydrophobicity refers to the poor affinity of water with contact angle (θ) > 150°. The superhydrophilic and superhydrophobic states of the solid surfaces are very important from the practical perspective than the intermediate stage between these two (10°< θ < 150°). The topic of superhydrophilicity is younger comparative to that of superhydrophobicity. The superhydrophilic surfaces are having unique properties such as fast water spreading and drying, antifogging, 6 antifouling, 7 etc., which are mainly useful for automobile mirror and glasses, 8,9 dental mirror, 10 bioactive implantation, 11,12 biocompatible materials, 13,14 humidity sen- sor, 15 microfluidic devices, 16,17 heat transfer enhancement, 18,19 and so on. Because of these wide varieties of applications of superhydrophilic surfaces, the topic has been drawing significant attention in recent years. There are mainly two strategies for generating a superhydrophilic surface. The first strategy is to develop surface modifications by various treatments (mentioned below) along with the surface rough- ness. The second one is by creating only micro/nanometer level roughness on the surface. There are many techniques available for the surface modification along with creation of surface roughness. Among these surface modification techni- ques, some important techniques are photo induced hydro- philicity (PIH) using UV light 20 and ion irradiation, 21 plasma treatment, 22 laser ablation, 23 and fluorine induced super- hydrophilicity (FIS). 24 Photo induced hydrophilicity was first reported in 1997 using polycrystalline TiO 2 thin film on glass surface. 25 When the TiO 2 coated surface was exposed to the UV radiation, the coating with submicron roughness was generated on the surface, and it became superhydrophilic. Later, coatings of other inorganic nanomaterials such as SnO 2 , ZnO, and WO 3 made through PIH were also reported by several researchers. 26-29 The disadvantage of this method is the functionalization can be made under irradiation of a specific light condition only. Plasma and corona treatments are also important techniques mainly applicable in the oxidation of polymer surfaces. 22 Recently, FIS based surfaces via oxy- fluoridation were also reported, in which fluorine atoms were linked to metal and semimetal atoms and a superhydrophilic surface was obtained. 24 In spite of the fact that the FIS surfaces show excellent antifogging property but the fabrication steps are tedious and complex. Received: September 20, 2016 Revised: January 5, 2017 Published: January 5, 2017 Article pubs.acs.org/JPCC © 2017 American Chemical Society 2428 DOI: 10.1021/acs.jpcc.6b09519 J. Phys. Chem. C 2017, 121, 2428-2436