Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion by Bharat Bhushan, Yong Chae Jung, and Kerstin Koch Philosophical Transactions A Volume 367(1894): May 13, 2009 ©2009 by The Royal Society

A schematic of condensed water vapour from the environment forming meniscus bridges at asperity contacts that lead to an intrinsic attractive force. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) SEM images (shown at three magnifications (i)–(iii)) of lotus (N. nucifera) leaf surface, which consists of a microstructure formed by papillose epidermal cells covered with three-dimensional epicuticular wax tubules on the surface, which create nanostr... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Schematic of a liquid droplet in contact with (i) a smooth solid surface (contact angle, θ0) and (ii) a rough solid surface (contact angle, θ), (b) contact angle for a rough surface (θ) as a function of the roughness factor (Rf) for various contact angl... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Schematic of the formation of a composite solid–liquid–air interface for a rough surface and (b) fLA requirement for a hydrophilic surface to become hydrophobic as a function of the roughness factor (Rf) and θ0 (Jung & Bhushan 2006). Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Tilted surface profile (tilt angle, α) with a liquid droplet; advancing and receding contact angles are θadv and θrec, respectively. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Schematic of the structure of an ideal hierarchical surface. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

SEM images of (a) the two nanopatterned polymer surfaces (shown using two magnifications to show both the asperity shape and the asperity pattern on the surface; (i)(ii) PMMA low aspect ratio (LAR) and (iii)(iv) PMMA high aspect ratio (HAR)) and (b) the mic... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Contact angles for various patterned surfaces on (a) PMMA and (b) PS polymers and values calculated using the Wenzel equation (Jung & Bhushan 2006). Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Surface height maps of the patterned Si surface (5 μm diameter, 10 μm height, 10 μm pitch pillars) using an optical profiler (Bhushan & Jung 2007) and (b) a liquid droplet suspended on a hydrophobic surface consisting of a regular array of circular pill... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Static contact angle (circles; the dotted line represents the transition criterion range obtained using equation (3.1)) and (b) contact angle hysteresis (circles) and tilt angle (triangles) as a function of pitch values for patterned surfaces (5 μm diam... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Evaporation of a droplet on a patterned surface. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Snapshots of a droplet with 1 mm radius hitting a patterned surface. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) Schematic of the two-step moulding process used to fabricate microstructure, in which at first (i) a negative is generated and then (ii) a positive. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Schematic of the thermal evaporation system for self-assembly of a wax. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Schematic of the glass recrystallization chamber used for wax tubule formation. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

SEM images of the morphology of lotus wax deposited on the flat epoxy replica surface after two treatments of specimens measured at 45° tilt angle: (a) after 7 days at 21°C, nanostructure on flat epoxy replica was found with no tubules; and (b) after 7 days... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) SEM images of the flat surface and nanostructures fabricated with various masses of n- hexatriacontane on epoxy resin measured at 45° tilt angle (shown using two magnifications; (i)(ii) flat, (iii)(iv) nanostructure (0.12 μg mm−2), (v)(vi) nanostructure... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) (i)–(iii) Bar charts showing the measured static contact angle, contact angle hysteresis and tilt angle, calculated contact angles obtained using Wenzel and Cassie–Baxter equations with a given value of θ0, and calculated contact angle hysteresis using... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

SEM images of (a) the flat surface, (b) nanostructure, (c) microstructure and (d) hierarchical structure measured at 45° tilt angle (shown using two magnifications (i)(ii)). Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a)–(c) Bar charts showing the measured static contact angle, contact angle hysteresis and tilt angle, calculated contact angles obtained using Wenzel and Cassie–Baxter equations with a given value of θ0, and calculated contact angle hysteresis using the Ca... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Evaporation of a droplet on (a) microstructured and (b) hierarchical structured surfaces. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

The remaining dust trace after droplet evaporation on (a) the microstructured and (b) the hierarchical structured surfaces. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) SEM images taken at 45° tilt angle (shown using two magnifications) of the (i–iv) nanostructure and (v–viii) hierarchical structure fabricated with two different masses ((i)(ii) and (v)(vi) 0.6 and (iii)(iv) and (vii)(viii) 0.8 μg mm−2) of T. majus wax... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a) (i)–(iii) Bar charts showing the measured static contact angle, contact angle hysteresis and tilt angle on various structures fabricated with 0.8 μm mm−2 mass of T. majus wax after storage at 50°C with ethanol vapour. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

SEM images taken at 45° tilt angle (shown using three magnifications) of (a(i–iii)) nanostructure on flat replica, (b(i–iii)) microstructures in lotus replica and (iv–vi) micropatterned Si replica and (c(i–iii)) hierarchical structure using lotus replica an... Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

(a)–(c) Bar charts showing the measured static contact angle, contact angle hysteresis and tilt angle on various structures fabricated with 0.8 μg mm−2 mass of lotus wax after storage at 50°C for 7 days with ethanol vapour. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Bar chart showing the remaining particles after self-cleaning experiments applying droplets with nearly zero kinetic energy on various structures fabricated from lotus wax using 1–10 and 10– 15 μm SiC particles. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society

Schematic showing wetting of the four different surfaces fabricated. Bharat Bhushan et al. Phil. Trans. R. Soc. A 2009;367: ©2009 by The Royal Society