Facile Adhesion-Tuning of Superhydrophobic Surfaces between “Lotus” and “Petal” Effect and Their Influence on Icing and Deicing Properties Md J. Nine, Tran Thanh Tung, Faisal Alotaibi, Diana N. H. Tran, and Dusan Losic* School of Chemical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia * S Supporting Information ABSTRACT: Adhesion behavior of superhydrophobic (SH) surfaces is an active research field related to various engineering applications in controlled microdroplet transportation, self-cleaning, deicing, biochemical separation, tissue engineering, and water harvesting. Herein, we report a facile approach to control droplet adhesion, bouncing and rolling on properties of SH surfaces by tuning their air-gap and roughness-height by altering the concentrations of poly dimethyl-siloxane (PDMS). The optimal use of PDMS (4-16 wt %) in a dual-scale (nano- and microparticles) composite enables control of the specific surface area (SSA), pore volume, and roughness of matrices that result in a well- controlled adhesion between water droplets and SH surfaces. The sliding angles of these surfaces were tuned to be varied between 2 ± 1 and 87 ± 2°, which are attributed to the transformation of the contact type between droplet and surface from “point contact” to “area contact”. We further explored the effectiveness of these low and high adhesive SH surfaces in icing and deicing actions, which provides a new insight into design highly efficient and low-cost ice-release surface for cold temperature applications. Low adhesion (lotus effect) surface with higher pore-volume exhibited relatively excellent ice-release properties with significant icing delay ability principally attributed to the large air gap in the coating matrix than SH matrix with high adhesion (petal effect). KEYWORDS: lotus effect, petal effect, roughness, porosity, superhydrophobicity, deicing 1. INTRODUCTION Superhydrophobic (SH) surfaces exhibit an extremely high water repellent behavior with a static contact angle (CA) greater than 150° and possess low CA-hysteresis. 1 Geometrical structures in nano/micro scale with di fferent chemical compositions affect surface free energy, roughness, specific surface area (SSA), and porosity of matrices, which are the key parameters to define different types of SH surfaces. 2 These active parameters by time have been revealed to play a significant role in tuning surface air pockets and contact area between water droplets and the SH surfaces, hence influences adhesion behaviors. In the early 1990s, the investigation of the microstructure of extremely water-repellent plant-leaves even- tually brings this concept of superhydrophobicity. 1 Subse- quently, different representative terms such as “lotus effect” and “petal effect” were coined to define antiadhesive and highly adhesive state of SH surfaces particularly observed in N. nucifera (indian lotus leaves) and rosea Rehd (red rose petal), respectively. A SH state with antiadhesive abilities, bouncing droplet, and small angle roll-off properties was called “lotus effect” coined by Barthlott and Neinhuis. 3 Recently, compared with the popular “lotus effect”, a new term “petal effect” was coined by Feng et al. 4 to define a SH state with a high adhesive force that sticks a water droplet at the interface, where the surface is turned upside-down. 4 These different states of wettability can be explained by classical theory of wettability on rough surfaces based on Cassie-Baxter (suspended state) and Wenzel (penetrated state) models. 5,6 Water can either penetrate the asperities or suspend above the asperities to create highly adhesive SH surfaces or very low adhesive SH surfaces, respectively. 2 Here, “lotus effect” actually follows Cassie-Baxter model addressing suspended droplet on the air-pockets trapped into rough surface, while “petal effect” is defined as an Cassie impregnating wetting state. 4 Many of the SH surfaces with various adhesion forces are actually tuned between Cassie and Wenzel states, 7 where this Cassie impregnating wetting state is an intermediate adhesive state. 8 The SH surfaces with the tunable adhesion forces have emerging applications in the field of controlled microdroplet transportation, 9 biochemical separation, 10 self-cleaning, 11 deic- ing, 12 cell adhesion/tissue engineering, 13,14 and vapor con- densation and collection. 15 A number of methods, such as Received: December 21, 2016 Accepted: February 13, 2017 Published: February 13, 2017 Research Article www.acsami.org © 2017 American Chemical Society 8393 DOI: 10.1021/acsami.6b16444 ACS Appl. Mater. Interfaces 2017, 9, 8393-8402