Design and engineering of sculptured nano-structures for application in hydrophobicity Somaye Hosseini a , Hadi Savaloni b, *, Mehran Gholipour Shahraki c a Department of Physics, Islamic Azad University, Science and Research Branch, Tehran, Iran b Department of Physics, University of Tehran, North-Kargar Street, Tehran, Iran c Department of Physics, University of Arak, Sardasht, Arak, Iran A R T I C L E I N F O Article history: Received 9 August 2016 Received in revised form 26 September 2016 Accepted 1 October 2016 Available online 10 October 2016 Keywords: Sculptured thin films Hydrophobicity Surface energy Cassie–Baxter state Wenzel state A B S T R A C T The design and engineering of suitable structures for enhancement of the hydrophobic property of a surface is one of the most challenging problems. In order to achieve a superhydrophobic structure we have designed and fabricated Mn nano-sculptured thin films with different shapes and dimensions, namely helical squares and helical pentagons on glass substrates. The contact angle (CA) of three liquids; a–bromonaphtalene (apolar), water and formamide (polar) to these surfaces was measured and the surface free energy was calculated. Changes to the geometry of the structure produced results ranging from hydrophilic (CA = 51  ) to superhydrophobic (CA = 152  ). The superhydrophobic structure is a helical square shaped structure with high porosity (deposited at 83  ) which also shows the rose petal effect with the additional property of high adhesion. The resemblance of this structure to that of gecko feet, which shows both high adhesion forces and superhydrophobic property is discussed. All structures investigated in this work showed negative spreading coefficients with highest values for the largest contact angle for each type/shape of structure. The superhydrophobic sample also acts as a sticky surface which is confirmed by hysteresis of the contact angle obtained from advancing and receding contact angles measurements. The influence of the volume of liquid drop and different surface morphologies on the wetting transition from Cassie–Baxter to Wenzel states is also reported. ã 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. Introduction Glancing angle deposition (GLAD) (deposition angle >85  ) or oblique angle deposition (OAD) (deposition angle <85  ) techni- ques are physical vapor deposition methods in which sculptured thin films can be engineered under controlled conditions. The rotation of the substrate about two axes provides the facility to produce three dimensional anisotropic nano-structures with different morphologies and high porosity. These structures are formed of columns with 1–100 nm diameter. The intriguing point in these sculptured structures is their controllable geometry and the potential use of vast number of materials for deposition which has led many researchers to investigate their different applications [1–5]. One of these applications is their use as hydrophobic or superhydrophobic surfaces, because of their controllable morphology. Recent investigations have shown that structures with low surface energy and high surface roughness usually lead to superhydrophobic phenomenon [6]. Both of these characteristics can be controlled in the process of GLAD/OAD sculptured thin films. Hence, in this work we investigate the applicability of this deposition method in the field of hydrophobicity by design and engineering of different shapes and morphologies. Wettability of a surface is usually defined by the size of the contact angle between the water/liquid drop and the solid surface. According to the size of this angle, surfaces are classified in three categories, namely hydrophilic (0  –90  ), hydrophobic (90  –150  ) and superhydrophobic (150  –180  ) [7–9]. Hydrophobic surfaces are usually formed either from materials with low surface energy or are produced using a two stage process; in the first stage, structures with micro/nano scale (hierarchical micro/nano-scale binary structures) features are formed and in the second stage some refinements/corrections are carried out to their surface using materials with low surface energy [10–12]. An alternative to the low surface energy approach utilizes contamination due to * Corresponding author. Fax: +98 21 88004781. E-mail addresses: savaloni@khayam.ut.ac.ir, savaloni@yahoo.com (H. Savaloni). http://dx.doi.org/10.1016/j.jiec.2016.10.008 1226-086X/ã 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. Journal of Industrial and Engineering Chemistry 45 (2017) 391–403 Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry journal homepa ge: www.elsev ier.com/locate/jie c