Cover
Title Page
Copyright
Preface
Chapter 1: Introduction for Biomimetic Superhydrophobic Materials
1. 1.1 Water Harvesting
2. 1.2 Self-Cleaning
3. 1.3 Corrosion Resistance
4. 1.4 Photochromism
5. 1.5 Robust and Durable Superhydrophobic Materials
6. 1.6 Transparent and Conductive Superhydrophobic Film
7. 1.7 Anti-fingerprint Superhydrophobic Film
8. 1.8 Anti-icing Ability
9. 1.9 Summary
10. References
Chapter 2: Superhydrophobic Surfaces from Nature and Beyond Nature
1. 2.1 Superhydrophobic Plant Surfaces in Nature
2. 2.2 Superhydrophobic Surfaces of Animals in Nature
3. 2.3 Chemical Composition of Plant and Animal Surfaces
4. 2.4 Inspired and Beyond Superhydrophobicity: from Natural to Biomimetic Structures
5. 2.5 Summary
6. References
Chapter 3: Advances in the Theory of Superhydrophobic Surfaces and Interfaces
1. 3.1 Basic Theories: Contact Angle and Young’s Equation
2. 3.2 Wenzel Model: Adaptability and Limitations
3. 3.3 Cassie–Baxter Model: Adaptability and Limitations
4. 3.4 Improved Models
5. 3.5 Cassie–Wenzel and Wenzel–Cassie Transitions on Superhydrophobic Surfaces
6. 3.6 Summary
7. References
Chapter 4: Fabrications of Noncoated Superhydrophobic Surfaces and Interfaces
1. 4.1 Etching Method
2. 4.2 Lithography
3. 4.3 Anodization
4. 4.4 Laser Processing
5. 4.5 Sol–Gel Process
6. 4.6 Electrodeposition
7. 4.7 Hydrothermal Method
8. 4.8 Direct Reproduction
9. 4.9 Other Fabrication Methods
10. 4.10 Summary
11. References
Chapter 5: Biomimetic Superhydrophobic Nanocoatings: From Materials to Fabrications and to Applications
1. 5.1 Materials for Nanocoatings
2. 5.2 Fabrications of Superhydrophobic Nanocoatings
3. 5.3 Biomimetic Transparent and Superhydrophobic Coating
4. 5.4 Summary
5. References
Chapter 6: Adhesion Behaviors on Superhydrophobic Surfaces and Interfaces
1. 6.1 Liquid–Solid Adhesion of Superhydrophobic Surfaces
2. 6.2 The Adhesion Conversion from Liquid–Solid to Solid–Solid States
3. 6.3 Solid–Solid Adhesion of Superhydrophobic Surfaces
4. 6.4 Summary
5. References
Chapter 7: Smart Biomimetic Superhydrophobic Materials with Switchable Wettability
1. 7.1 Single-Response Smart Responsive Surfaces
2. 7.2 Dual-Responsive and Multiple-Responsive Surfaces
3. 7.3 Summary
4. References
Chapter 8: Biomimetic Superhydrophobic Materials Applied for Oil/Water Separation (I)
1. 8.1 Metallic Mesh-Based Materials
2. 8.2 Fabric-Based Materials
3. 8.3 Sponge and Foam-Based Materials
4. 8.4 Particles and Powdered Materials
5. 8.5 Other Bulk Materials
6. 8.6 Theories Underlying Oil/Water Separation Behavior
7. 8.7 Summary
8. References
Chapter 9: Biomimetic Superhydrophobic Materials Applied for Oil/Water Separation (II)
1. 9.1 The Formation of Oil/Water Emulsions
2. 9.2 Modified Ceramic Separation Membranes
3. 9.3 Polymer-Based Separation Membranes
4. 9.4 Inorganic Carbon-Based Membranes
5. 9.5 Non-Two-Dimensional Separating Methods
6. 9.6 Summary
7. References
Chapter 10: Biomimetic Superhydrophobic Materials Applied for Anti-icing/Frosting
1. 10.1 Introduction of Anti-icing/Frosting
2. 10.2 Ice and Frost Formation Mechanism
3. 10.3 Natural Superhydrophobic and Icephobic Examples
4. 10.4 Anti-icing Performances of SHPSs under Various Situations
5. 10.5 Design and Icing-Delay Performances of SLIPSs
6. 10.6 Icephobic Performances of SHPSs
7. 10.7 Icephobic Performances of Advanced Surfaces and Techniques
8. 10.8 Theories behind Anti-icing Research
9. 10.9 Summary
10. References
Chapter 11: Conclusions and Outlook
Index
End User License Agreement

List of Illustrations

Chapter 1: Introduction for Biomimetic Superhydrophobic Materials
1. Figure 1.1 (a) Schematic of the fabrication of cactus-inspired conical arrays and (b) the magnetically induced conical array responses. (c) Charge-coupled device (CCD) camera observations in response to a magnet. Scale bar: 1 mm. (d) Magnetically driven cone and (e) a static cone placed in the same fog chamber at different time periods.
2. Figure 1.2 (a) Relationship between the critical velocity (V_critical) and the concentration of the PMMA/DMF solution. The spindle-knots could be constructed when V > V_critical, or vice versa. (b) Size of the spindle-knots as a function of the drawing velocity. (c–g) Directional water-collection process on a bioinspired fiber with a PMMA spindle-knot.
3. Figure 1.3 (a, b) Digital photographs of a coated white fabric used in antifouling
4. Figure 1.4 (a) Photographs of an oil droplet on the TiO₂ flower coatings after contamination treatment and UV irradiation. (b) Reversible changes of OCA on the sample during cyclic alternations of contamination treatment and UV irradiation.
5. Figure 1.5 Polarization curves of the Al sheet: (a) clean and (b) PS-modified.
6. Figure 1.6 Tafel plots for bare stainless steel, stainless steel coated with PANI, PANI-PEG1, PANI-CTAB1, and PANI-SDBS1 [20].
7. Figure 1.7 (a) Top view and (b) side view of typical SEM images of tungsten oxide films deposited from the electrolyte at a pH of ~8.6. (c) Absorption spectra of an electrodeposited tungsten oxide film before (solid line) and after (dashed line) UV light irradiation. The insert shows the photochromic switching of the absorption change (monitored at 372 nm) during consecutive cycles of UV irradiation and storage in the dark.
8. Figure 1.8 Effect of laundering cycles on the contact angle and adhesive force of TiO₂@cotton fabrics according to AATCC standard method. The insets are the corresponding contact angle images with different laundering cycles.
9. Figure 1.9 Photographs of the flame retardancy test of (a) uncoated and (b, c) coated cloth with different ignition durations (1 and 5 s, respectively).
10. Figure 1.10 Ice formation, adhesion, and de-icing characteristics. Digital images of ice layers formed on (a) SF, (b) FF, and (c) LF under mimicked freezing rain environment. (d) Average ice adhesion strength on different films. Laser-induced photothermal deicing. (e) Schematic of the photothermal rapid de-icing process. (f) Plots of surface temperature with irradiation time at room temperature. (g) Captured images from the de-icing videos, showing the ice melting process on SF and LF at different times.
Chapter 2: Superhydrophobic Surfaces from Nature and Beyond Nature
1. Figure 2.1 Superhydrophobic and self-cleaning of the lotus surface. (a) A flowering plant of lotus.
2. Figure 2.2 Morphologies of S. molesta floating leaf. (a) Upper side of the leaf surface densely covered with hairs. The spherical shape of the water drop on the leaf indicates the superhydrophobic character of the surface. (b) Four multicellular hairs grouped on top of an emergence and connected at the terminal end leading to an eggbeater-shaped structure. (c) The terminal cell of each hair is collapsed forming a patch of four dead cells. (d) The whole leaf surface is covered with nanoscale wax crystals (below) with exception of the terminal cells (above). (e) Low-temperature SEM of a frozen leaf with applied droplet of a water–glycerol solution. (f) Lateral view of the contact zone showing a hydrophilic meniscus between the water–glycerol droplet and the terminal cells.
3. Figure 2.3 (a) SEM image of the dried rose petal; the inset shows the photograph of the rose petal. (b) A water droplet, CA and SA of the dried rose petal. (c) Magnified SEM image of the rose petal surface. (d) Profile of the dried rose petal (the height of the micropapillaes on the petal was measured to be ~24.5 µm). (e) Magnified SEM image of a micropapilla. Nanogrooves can be seen on both the top and the walls of the micropapillae. (f) SEM image of the nanograting structure on the wall of the micropapillae.
4. Figure 2.4 Photographs of creatures with superoleophobic surfaces in Nature. (a) (left) Orthonychiurus stachianus immersed in ethanol resists wetting through the formation of a shiny air cushion, and (right) SEM images of O. stachianus at different magnifications
5. Figure 2.5 Development of the plant cuticle. In the early leaf epidermis, rapidly dividing cells are covered with a highly water repellent wax layer, the procuticle (a). This amorphous wax layer is added to as the leaf expands (b–d). (b) Lamellation of the procuticle occurs by the deposition of polysaccharides and cutin layers and becomes the cuticle proper (CP). (c) Epicuticular waxes (EPW) are deposited on the outermost surface of the cuticle in a film, and the primary cell wall (PCW) becomes fibrous and incorporated into the cuticle layer. The secondary cell wall (SCW) forms beneath the primary cell wall. (d) Two thick polymerized cutin layers (internal cutin layer, ICL; and external cutin layer, ECL) are deposited, and are discernable by their structure and chemical compositions. In some plant species, as more wax is deposited, wax crystals form over the amorphous wax film.
6. Figure 2.6 SEM micrographs of epicuticular waxes. (a) Thin wax film in Hydrocotyle bonariensis that is not visible in SEM covering many plant surfaces. (b) A wax crust with fissures on a leaf of Crassula ovata. (c) Cross-section through the periclinal wall of Aloe striata showing the cuticle (indicated by C) and a wax layer (indicated by an arrow) with wax platelets on top. (d) Nonacosan-ol tubules on Thalictrum flavum glaucum leaves. (e) β-Diketone wax tubules of Eucalyptus gunnii. (f) Wax platelets on Robinia pseudoacacia leaves arranged in rosettes. (g) Transversely ridged rodlets on a leaf of Sassafras albidum. (h) Longitudinally aggregated wax threads forming large crystals on the lower side of the leaves of Musa species. (i) Wax platelets in Convallaria majalis leaves, which are arranged in a specific pattern around the stomata.
7. Figure 2.7 (a) SEM image of film I fabricated from a 5 wt% PS/DMF solution. (b) Magnified image of porous microparticles. (c) Water droplet on film I. (d) SEM image of film II prepared from a 25 wt% PS/DMF solution. (e) Magnified part of (d). Water droplets on film II (f). (g) SEM image of PMNCF with 3D network structure prepared from a 7 wt% PS/DMF solution. (h) Surface nanostructure of a single porous microsphere. (i) Water droplet on PMNCF.
8. Figure 2.8 SEM images of the imprinted layers of BP-AZ-CA. (a) Top view of the surface. (b) Wide view of (a). (c) Sectional view of the surface. (d) Wide view of (c). The inset gives the surface morphology of a single papilla.
9. Figure 2.9 (a) SEM image of a silver-coated rose petal. The inset shows the photograph of the silver-coated rose petal. (b) SEM image of a single silver-coated micropapilla. (c) A water droplet CA and SA of the rose petal after silver coating. (d) Magnified SEM image of the top of a micropapilla; nanogrooves can be seen on the top. The inset shows the high-resolution SEM image of the nanogrooves surface, on which silver nanoparticles can be identified. (e) Magnified SEM image of the nanograting on the wall of the micropapilla
10. Figure 2.10 (a) Schematic of the fabrication process for parylene nanofibrils. (b) and (c) SEM image of the resulting densely packed nanofibrils with different magnifications.
Chapter 3: Advances in the Theory of Superhydrophobic Surfaces and Interfaces
1. Figure 3.1 (a) Schematic diagram of a liquid droplet on a flat, smooth solid surface. (b) Sketch map presenting a simple derivation of Young’s equation on a flat, smooth solid substrate.
2. Figure 3.2 Schematic diagrams of liquid droplets on micro-structured surfaces under the homogeneous (Wenzel) regime.
3. Figure 3.3 Schematic diagrams of (a) a liquid droplet on a micro-structured surface under the heterogeneous (Cassie-Baxter) regime, and (b) a liquid droplet on the micro-structured surface under the Impregnating Cassie wetting regime.
4. Figure 3.4 Scanning electron microscopy (SEM) images of a lotus leaf surface with a hierarchical structure. (a) Nano-scale asperities and micro-scale bumps of a lotus leaf surface. (b) Water on the lotus leaf surface.
5. Figure 3.5 Schematic illustrations of a drop residing on a hierarchical structure corresponding to (a) high adhesion and (b) low adhesion [39].
6. Figure 3.6 Fractal surface showing self-similarity with the resolution increase.
7. Figure 3.7 (a) Advancing angle when the drop volume is increasing, and (b) receding angle when the drop volume is decreasing [75].
8. Figure 3.8 Liquid front in contact with a rough solid surface, propagating along the curved surface along the horizontal surface.
Chapter 4: Fabrications of Noncoated Superhydrophobic Surfaces and Interfaces
1. Figure 4.1 SEM images of etching. (a, b) Cross sections of PDMS microchannels etched for 45 min in a quartz dome reactor. (a) SU-8 was used directly on PDMS and (b) on Al layer. (c–e) 30 min SF₆ etched PDMS microchannel (15 µm deep). (a) prior to wet etching, (b) after 2 min, (c) 30 min immersion in BHF.
2. Figure 4.2 (a) Schematic of the optical setup. (b) Schematic of laser polishing by remelting a thin surface layer with continuous wave laser radiation. (c) Schematic of selective laser polishing. (d) Photograph of a selective laser polished leather textured free-form surface.
3. Figure 4.3 (a) One-pot synthetic process of the VTMS-VMDMS marshmallow-like gel (MG1). (b) Synthetic process for the oleophobic gel MG2. (c) SEM image of MG1. (d) SEM image of MG2. No changes can be found in the macroporous morphology in the reaction.
4. Figure 4.4 Schematic diagrams of the surface with switchable wettability by ion exchange.
5. Figure 4.5 (a) Optical images of UV reversibly switchable wettability of ZnO with a nanocolumnar morphology. (b) Schematic representations of UV reversibly switchable wettability of ZnO with a nanocolumnar morphology.
6. Figure 4.6 (a) Schematic diagram of the MSIP process [138]. (b) The schematic diagram of preparation of transparent and stable superhydrophobic coating.
Chapter 5: Biomimetic Superhydrophobic Nanocoatings: From Materials to Fabrications and to Applications
1. Figure 5.1 (a) (Top) SEM image of the superhydrophobic composite surface. The sample was drop-cast from a chloroform solution on to a copper grid. (Bottom) AFM images of the OPV1–MWNT composite coating.
2. Figure 5.2 (a) TEM micrograph of an isolated nano-rod showing a silver core and a TiO₂ shell.
3. Figure 5.3 (a) Side-on SEM image of a polymer film with embedded anatase TiO₂ NPs deposited using AACVD.
4. Figure 5.4 (a) comparison between precursors withdifferent alkyl chain lengths (PEDOP-H₂, PEDOP-H₆, and PEDOP-H₁₄) electrodeposited under the same conditions.
5. Figure 5.5 (a) Schematic illustrations of the synthesis of transparent superamphiphobic coating by spray coating of stringed silica NPs. (b) SEM images of the superamphiphobic coating with a network of stringed silica NPs.
6. Figure 5.6 (a) Schematic illustration of the strategy to fabricate raspberry-like SiO₂/PS composite coatings. (b) TEM images of SiO₂/PS composite particles. (c) SEM images of the film made of the as-prepared raspberry-like SiO₂/PS composite particles.
7. Figure 5.7 (a) Schematic illustration of a branched silica nanoparticle. (b) High-resolution SEM image of the cross-section (fractured) of the SNANPS, revealing its surface micro/nano hierarchical structures.
8. Figure 5.8 (a) Schematic representation of the process of fabrication of nano-textured silica/titania films on arbitrary substrates. (b) SEM image of close observation of the film from a splinter. (c) The as-prepared coating showing semitransparency without losing the superhydrophobicity.
9. Figure 5.9 (a) Sketch map of the experimental unit. (b) SEM images of the PTFE film on a flat silica substrate. (c) Optical images of water droplets (3 µl) on the PTFE surface of the flat glass substrate. (d) SEM images of the PFA film on the flat silica substrate. (e) Optical images of water droplets (3 µl) on the PFA surface of the flat glass substrate.
10. Figure 5.10 Schematic illustration of the fabrication procedure for superhydrophobic, transparent PMMA surfaces. Water immersion was employed to remove the capping layer (colored in white).
11. Figure 5.11 (a) Scheme of the hydrogen-bond-driven stabilization of a CNT solution. (b) Image of a stabilized t-MWNT/silane sol solution. (c) FESEM image of a spray-coated t-MWNT/silane hybrid film. (d) Water droplets on this film.
12. Figure 5.12 (a) Photograph of a PU/TMS-SiO₂ coating with red fluorescence and high transparency (taken under UV lamp) [144]. (b) Variation of CA on the PU/TMS-SiO₂ coatings with the drying temperature. (c,d) FE-SEM images of PU/TMS-SiO₂ coatings drying at 20 and 150 °C.
13. Figure 5.13 (a) Colored water droplets sitting on OTES−TEOS-treated cotton fabrics; the transparency does not alter after coating.
Chapter 6: Adhesion Behaviors on Superhydrophobic Surfaces and Interfaces
1. Figure 6.1 (a) Photographs of lotus leaf and its scanning electron microscopy (SEM) images, (b) pictures exhibiting multiscale structural hierarchy in gecko foot hair, and (c) schematic illustration of structural compliance and adaptation against different rough surfaces.
2. Figure 6.2 (a) The optical image of a butterfly, (b–d) SEM images of a butterfly’s wing with different magnifications.
3. Figure 6.3 Schematic illustration of three types of superhydrophobic porous nanostructure models with different water adhesive forces. (a) Capillary adhesion will arise when a water droplet sitting on the tube nozzle is gradually drawn upward. (b) Superhydrophobic NPA with high adhesion. (c) Superhydrophobic NTA with controllable adhesion. (d) Superhydrophobic NVS with extremely low adhesion.
4. Figure 6.4 Photo-induced changes of superhydrophobic adhesion on micro-nanopost array with azo-polymer coating.
5. Figure 6.5 The changes of superhydrophobic adhesions with magnetization and demagnetization: (a) A low adhesion before magnetization and high adhesion after magnetization. (b) The relationship between magnetic field intensity and adhesion force before and after magnetization. (c) Schematic diagram of transition between high adhesion and low adhesion.
6. Figure 6.6 (a) The equipment schematic of electrocontrolled adhesion. (b) Relationship between voltage droplet for positive and negative bias voltages and CA, respectively. (c) Relationship between voltage droplet for positive and negative bias voltages and hysteresis angles, respectively. (d) Schematic of water droplets on nanotube structured surfaces before and after supplying voltage.
7. Figure 6.7 (a) Schematic model of the spherical surface of a pillar array and the curvature calculation. (b) The relationship between the curvature and CA. (c) relationship between adhesion forces and curvatures lengthens the distance between adjacent pillar tips. (d) Schematic of curvature-driven reversible adhesion.
8. Figure 6.8 SEM images of the nanostructured films on PDMS microwavy structures with a different number of deposition cycles; (a–c) are the number of PAH/SN bilayers, indicating 2, 5, and 9, respectively. (d–f) Relationship between static water contact angles (d), roll-off angles (e), and contact angle hysteresis (f) perpendicular (black squares) or parallel (white dots) with the roughness of nanostructure (R_q).
9. Figure 6.9 In situ observation of ice formation on micro-/nanostructured (MN-), nanostructured (N-), microstructured (M-), and smooth (S-) surfaces at −10 °C with delay times (DT).
10. Figure 6.10 Optical microscope images showing the antibacterial activity of as-prepared Fe₃O₄ NPs, Fe₃O₄@PDA NPs, and Fe₃O₄@PDA@Ag NPs on the agar plate inoculated with E. coli. Zones of bacterial colony on the NPs region are indicated by red arrows. (a) Antibacterial activity of Fe₃O₄ NPs. (b) Antibacterial activity of Fe₃O₄ @PDA NPs. (c) Antibacterial activity of Fe₃O₄ @PDA@Ag NPs. (d) The overall appearances of the antibacterial activity before and after culturation of 1 day of E. coli under constant temperature of 37 °C.
Chapter 7: Smart Biomimetic Superhydrophobic Materials with Switchable Wettability
1. Figure 7.1 (a) SEM images showing the side view of gold aggregates deposited on a silicon wafer; these aggregates are rough, three-dimensional structures with tree-like microstructures. (b) Photographs of basic, and (c) acidic droplets on roughened and modified gold surfaces. The CA of the basic droplet was 152°. When an acidic water droplet was applied, the CA decreased to superhydrophilicity within a total of 10 s. (d) Illustration of the various surface properties available to the mixed SAM under different pH conditions.
2. Figure 7.2 (a) Mechanism of photocatalytic activity of Cu₂O-doped nano-TiO₂. SEM images of Cu₂O-doped nano-TiO₂-treated fabrics, Sample 9 (0.03% CuSO₄·5H₂O and 0.12% glucose at pH = 11). (b) ×1000, (c) ×8000, and (d) ×50000.
3. Figure 7.3 (a) Schematic diagram of the reversible competition between inter- and intramolecular hydrogen bonding, which is the molecular mechanism of the temperature-responsive switching on a PNIPAAm film. (b) Water-drop profile for thermally responsive switching between superhydrophobicity and superhydrophilicity of PNIPAAm-modified micro- and nanostructured Si surfaces at 25 (left) and 40 °C (right) [80].
4. Figure 7.4 (a) Diagram of reversible formation of intermolecular hydrogen bonding between PNIPAAm chains and water molecules below the LCST, which leads to hydrophilicity/oleophobicity, and intramolecular hydrogen bonding between C═O and N─H groups in PNIPAAm chains above the LCST, which leads to hydrophobicity/oleophilicity. (b) Temperature dependences of water and oil CAs for a PMMA-b-PNIPAAm film. The water CAs change from 42° to 107° (I) and the OCAs change from 137° to 36° (II) with the temperature increasing from 10 to 40 °C. Inset images (1–4) are the CA/OCA obtained at 10 and 40 °C, respectively. (c) Reversible water and oil CA transition of the BCP film at different temperatures (10 °C < LCST; 40 °C, >LCST), indicating excellent reproducibility and stability.
5. Figure 7.5 (a) Schematic outline of the procedure used to prepare the textured surfaces with tunable wettability. (b) Photographs of water droplets on a smooth substrate and a rough substrate. The water contact angle varies from 90° ± 2° to 65° ± 1° on the flat substrate, whereas it changes from 171° ± 3° to below 5° on the gold clustered surface, indicating that switching between superhydrophobicity and superhydrophilicity results from replacing the TFSI ions with SCN⁻.
6. Figure 7.6 Schematic of two amide stereoisomers involved in a reversible change upon alternating treatment with ethanol and cyclohexane.
7. Figure 7.7 SEM images of a typical microfabricated silicon mold: (a) general mold overview (top view) and (b) cross section obtained after cleaving the wafer. (c) Cilia rotation in response to an external rotating magnetic field. Total time: 2 s.
8. Figure 7.8 (a) SEM images of α-MnO₂ nanotube membranes. The inset in (b) shows the typical tubular structure with a square open end. (c) Apparent contact angle variation of a deionized water droplet for positive and negative bias voltages. (d) Schematic illustration of the transition of water droplet behavior induced by the electric field. The lower part displays different contact geometries and possible three-phase contact line (TCL) with and without bias, respectively.
9. Figure 7.9 The wettability control of a stretch-responsive composite material. (a) The surface exhibits a negligible contact angle when the glass particles are not silanized and becomes superhydrophobic after silanization. After silanization, the surface becomes superhydrophilic when the material is stretched. (b) The transition between superhydrophobicity and superhydrophilicity is reversible. The material shows great stability with a contact angle maintained ≈0° when stretched and CA >150° when released even when it is stretched and released 20 times. (c) The contact angle can be adjusted by stretching the material to different extents; (d) SEM image of the glass particles on the surface.
10. Figure 7.10 Contact angles on the flat substrate, and hypothetical diagram of the reversible formation of inter- or intramolecular hydrogen bonding between NIPAAM-co-PBA chains, water, and glucose molecules. (a) Variation of CA with temperature at pH 7.4 and (glucose) = 8.6 g l⁻¹. (b) Variation of CA with pH at T = 26 °C and (glucose) = 8.6 g l⁻¹. (c) Variation of CA with (glucose) at pH 7.4 and T = 26 °C.
11. Figure 7.11 Contact angles on the rough substrate. (a) At pH 7.4 and a glucose concentration of 8.6 g l⁻¹, the CAs changed with temperature from 13.3° ± 1.6° to 152.7° ± 5.0°. (b) At T = 26 °C and (glucose) = 8.6 g l⁻¹, the CAs changed with pH from 145.4° ± 2.3° to 22° ± 6.3°. (c) At pH 7.4 and T = 26 °C, the CAs changed with glucose concentration from 15.4° ± 3.8° to 145.5° ± 2.6°.
Chapter 8: Biomimetic Superhydrophobic Materials Applied for Oil/Water Separation (I)
1. Figure 8.1 (a) Scanning electron microscopy (SEM) images of the coating mesh film with an average pore diameter of about 115 µm. (b) Enlarged views of (a). (c) A water droplet on the as-prepared mesh film with WCA of 156 ± 2.8°. (d) A diesel oil droplet spread and penetrated the as-prepared mesh film within 240 ms. (e) Relationship between the pore diameters and water contact angles when a water droplet on the prepared mesh film.
2. Figure 8.2 Oil/water separation studies of the PAM hydrogel-coated mesh.
3. Figure 8.3 Schematic representation of the preparation of superhydrophobic fabric.
4. Figure 8.4 (a–d) Time sequence of the oil/water separation procedure with superhydrophilic TiO₂@Cotton membrane for the selective permeation of methyl blue dyed water. Time sequence of (e–g) capture oil layer (petroleum ether dyed red) on water surface, and (h–j) underwater oil droplets (chloroform dyed red) with superhydrophobic fabrics.
5. Figure 8.5 (a) Digital photograph of the carbon–silica sponge regeneration by mechanical compression. Acetone was used and dyed with red for clear presentation. (b) Photograph showing densification of the sponge and the subsequent recovery upon isooctane sorption and/or after drying. The recyclability and recovery studies of carbon–silica sponge over five to six cycles of (c) distillation and (d) squeezing by using isopropyl alcohol as sorbate.
6. Figure 8.6 CAs of the (a) original, (b) KH, (c) GN, and (d) KH–GN sponges. (e) Photographs of water droplets on the original and KH–GN sponges. (f) Photographs of water droplets and a diesel oil droplet on the KH–GN sponge. (g) Photographic image of a water column squirted onto the KH–GN sponge (L-left, R-right).
7. Figure 8.7 (a) Schematic illustration describing the mechanism of mixing driven phase separation, precipitation polymerization, and subsequent pore formation after removal of porogen PDMS oil. (b–e) SEM images of the surface and the three different layers within the porous particle.
Chapter 9: Biomimetic Superhydrophobic Materials Applied for Oil/Water Separation (II)
1. Figure 9.1 Effect of oil content on the phase separation of emulsions stabilized by 4.0% GA/1.0% SBP after 24 h of storage at 25 °C. The concentration of the oil phase in the emulsions is 0.1%, 0.2%, 0.5%, 1.0%, 2.0%, 5.0%, and 10.0% (from left to right), respectively.
2. Figure 9.2 (a) Schematic of separating a surfactant-stabilized water-in-oil emulsion. (b) Filtration rate and (c) separation efficiency of various water-in-oil emulsions on the membrane.
3. Figure 9.3 (a) Chemical structure of N-substituted polyurethanes. (b) Schematic illustration of nanofibrous membranes with self-healing ability for oil/water emulsion separation. (c) Self-healing mechanism of the electrospun membrane.
4. Figure 9.4 Schematic illustration of the formation of a superhydrophobic–superoleophilic PVDF membrane via a modified phase-inversion process.
5. Figure 9.5 (a) Formation of a superhydrophilic underwater superoleophobic PAA-g-PVDF membrane by a salt-induced phase-inversion process. (b) Photograph of an as-prepared PAA-g-PVDF membrane. (c) Cross-section and (d) top-view SEM images of the membrane. Photographs of (e) an underwater oil droplet and (f) a water droplet on the membrane.
6. Figure 9.6 (a) Schematic showing the separation of water-in-oil emulsions by free-standing ultrathin SWCNT films. (b) TEM image of SWCNT film. Optical images of the SWCNT film (c) floating on an acetone/water surface and (d) suspended by a steel hoop on which water and oil CAs were measured. (e) Photographs of a water droplet and an oil (dichloromethane) droplet on the SWCNT film. (f) Average pore size versus thickness of the SWCNT film.
7. Figure 9.7 FESEM images of a PA support surface at (a) low and (b) high magnification; (c,d) a 15-nm GO coated surface at (a) low and (d) high magnification; and (e,f) a 50-nm GO coated surface at (a) low and (f) high magnification. Red and blue arrows point to areas that were wrapped and covered by GO flakes, respectively.
8. Figure 9.8 Programmed perforation process to fabricate dual-scaled porous NC membrane for oil/water separation.
9. Figure 9.9 Separation of an oil-in-water emulsion. (a) Hexane-in-water emulsion before and after separating. Scale bar 100 µm. (b) Separation efficiency of SDBS-stabilized hexane-in-water emulsions containing 10, 20, and 30 vol% hexane, respectively. (c) Separation efficiency of various types of surfactant-stabilized hexane-in-water emulsions containing 10 vol% hexane. (d) Separation capacity and flux of SDBS-stabilized hexane-in-water (5 : 95, v:v), SDBS-stabilized diesel-in-water (5 : 95, v:v), and SDBS-stabilized gasoline-in-water (5 : 95, v/v) emulsion.
10. Figure 9.10 (a) Photographs of the oil collection apparatus continuously collecting floating oil (n-hexane dyed in red) on a moving water surface [41]. (b) Schematic drawing of the synthesis procedure of the superhydrophobic PANI-coated fabric.
Chapter 10: Biomimetic Superhydrophobic Materials Applied for Anti-icing/Frosting
1. Figure 10.1 (a) Time axis of the anti-icing/de-icing evolution from traditional anti-icing/de-icing methods (first generation) to superhydrophobic anti-icing and icephobic surfaces (second generation). (b) Annual percentage of published papers on special wettability stimulated anti-icing research.
2. Figure 10.2 (a) Phase diagram of water, showing the three pathways for ice formation. (b) Curve of Gibbs free energy ΔG (Homo-N) changing with ice embryo radius r. r* and ΔG*, respectively, denote the critical radius and corresponding maximum energy barrier. (c) Freezing process of a sessile water droplet on a supercooled SHPS under unsaturated shear gas flow [46]. (d) Schematic diagram illustrating the phenomenon in (c), where the concept of evaporative cooling is shown.
3. Figure 10.3 (a, b) Variation of the parameter f versus the geometrical ratio x (x = R/r*) for (a) convex nano-bump surface (f_V) and (b) concave nano-pit surface (f_C), deduced from classical nucleation theory. (c) Schematic of the presence of interfacial quasi-liquid layer between an ice embryo and a solid surface in a nano-pit. (d) A hypothetical surface predicted with extremely low ice nucleation temperature.
4. Figure 10.4 (a) Top view of a supercooled water droplet. (b) Evaporation-controlled condensation halo (area between white and black dashed circle) during droplet freezing. (c) Magnified segment of the formed condensate halo. (d) Partial crystallization of the condensate during re-evaporation. (e1–3) Ice-bridge-dependent freezing of two neighboring droplets.
5. Figure 10.5 Natural superhydrophobic examples of (a) mosquito’s eyes and (e) butterfly’s wings. (b–d) SEM images of mosquito’s eye [124]. (f–h) SEM images of butterfly’s wing. (i1–4) Schematic diagram to illustrate the stable superhydrophobicity and enhanced water repellency of butterfly’s wing.
6. Figure 10.6 Natural icephobic examples of (a) the pitcher plant and (e) skunk cabbage. (b, c) SEM images of the pitcher plant surface [130]. (d) SLIPS model inspired from the pitcher plant [131]. (f, g) SEM images of skunk cabbage leaf. (h) SLLWL model inspired from skunk cabbage.
7. Figure 10.7 Anti-icing superhydrophobic coating. (a) Uncoated side and (b) coated side of the aluminum plate after the natural “freezing rain.” (c) Satellite dish antenna where one half is coated with a superhydrophobic composite after the freezing rain. (d) Close-up view of the area labeled by a red square in (c).
8. Figure 10.8 Anti-icing performance and construction of low-hysteresis SHPSs. (a, b) Anti-icing test by depositing supercooled water droplets on the general surface and the SHPS when titled [78]. (c–f) Pictorial surface patterns with different structure types due to very discontinuous or continuous contact lines (TPCLs).
9. Figure 10.9 Freezing process of water droplets on a cold (a) smooth surface (SS), (b) micro-structured surface (MS), (c) nano-strutured surface (NS), and (d) micro-/nano-structured surface (MNS) at −10 °C. The whole freezing process consists of a precooling stage and the ice growth stage.
10. Figure 10.10 (a) Metal surface with nano-hairs over micro-ratchets (MN-) with a droplet freezing time of 7220 s [83]. (b) Gummed tape with nano-cones over PVDF microspheres with the droplet freezing time of 126 min [84]. (c) Organic–inorganic hybrid superhydrophobic coating with the droplet freezing time of 10 054 s [86]. (d) Ag-deposited PU sponge surface with the droplet freezing time of 126 min [88]. (e) Portion of the frozen droplets over time under isothermal condition (T = −8 °C) and a saturated vapor atmosphere (RH = 100%).
11. Figure 10.11 (a) Beneficial role of hierarchical morphology in determining the impact resistance at a substrate temperature of −30 °C. (b) SEM images of the top of the micro-pillars according to the micro and hierarchical morphologies in schematics in (a). Hierarchical SHPS with minimal spacing between the asperities, both at the micro- and nanoscales, yielding best impalement resistance among surfaces with the same solid fraction [92]. (c–e) Top-view optical images of (c, d) open-cell nanopost structures and (e) a closed-cell brick structure. Insets show the impact droplet (~15 µl, from a 10 cm height at T_room) can rebound on (d) posts with small spacing and (d) bricks, while fails to rebound on posts with larger spacing showing low pressure stability.
12. Figure 10.12 (a–c) Ice accumulation on (a) flat aluminum, (b) smooth fluorinated Si, and (c) microstructured fluorinated Si surfaces (T_substrate = −10 °C) tilted at 30°. (d) Micrographs of (c) exemplary SHPSs: posts, bricks, blades, and honeycombs. Ice accumulation is observed on both (a) hydrophilic and (b) hydrophobic surfaces, while no freezing or accumulation is observed on the SHPS even after a significant period upon the impact of a droplet stream (T_droplet = 0 °C) from a 10 cm height at a rate of 0.06 ml/section (e, f) Still images depicting dynamic retraction and rebound behavior of supercooled droplets (−5 °C) as a function of substrate temperature on (e) the flat surface and (f) the SHPS. The sudden pinning transition happens upon decrease of the surface temperature.
13. Figure 10.13 (a) SEM images of fabricated silicon SHPS consisting of macroscale ridges and hierarchical micro/nanoscale features by laser ablation. (b) Non-axisymmetric recoil behavior and shortened contact time of 3.4 ms on surface (a) [213]. (c) SEM images of the copper SHPS patterned with a square lattice of tapered posts covered by nanoflowers. (d, e) Selected snapshots showing a droplet impacting and bouncing off (d) the horizontal surface at ~3.4 ms at We = 14.1 and (e) the tilted surface (30°) at ~4.2 ms at We = 31.2 in a pancake shape.
14. Figure 10.14 Classification of snapshot images and sketches of droplet rebound, disengagement, and post-impact outcomes after impacting on inclined and horizontal SHPSs. The droplet rebound characteristics on inclined surfaces can be classified into eight different outcomes driven primarily by normal Weber number and drop Ohnesorge number.
15. Figure 10.15 (a) Overlapped optical image showing a continuous coalescence-induced jumping process of condensed microdroplets. (b) Three fundamentally different removal mechanisms: two-droplet, multi-droplet, and multi-hop jumping [241]. (c) Schematic illustration of enhanced jumping droplet condensation on (d) SHPS with a micropore array at a high supersaturation. (e) Anti-frosting tests of a normal Al surface (sample A), a nanostructured SHPS (sample B), and an SHPS with a 10 mm micropore array. The images highlighted by red lines indicate that the entire surface is covered by the frost layer.
16. Figure 10.16 (a) SEM image of a flake-like CuO superhydrophobic tube after 10 min oxidization. (b, c) Optical images of jumping droplet condensation under a negative electric field and a positive electric field. (d) Optical image of the condensation beneath the CuO tube. Some droplets leave the tube (blue dotted arrows), while others return toward the tube surface (black dotted arrows).
17. Figure 10.17 (a) Selected images showing the evaporation and ice bridging process of condensed droplets on an SHPS. (b, c) Schematic illustrating the roles of droplet size (diameter D), density (spacing L), and evaporation rate in the ice bridging dynamic in (a). Gray parts represent the icing areas, while blue parts represent the liquid condensed droplets [99]. (d, e) Histograms of the statistical percentage of liquid droplet size distribution and bridging parameter S* on hydrophobic (HPB, dark blue histograms) and superhydrophobic (SHPS, light blue histograms) surfaces at −10 °C during ice bridge growth [260].
18. Figure 10.18 (a) Surface morphology of prepared flower-like copper SHPS. (b, c) Edge-initiated violent icing tendency both upfacing (left) and downfacing (right) copper SHPS at the time point of 93 and 97 min, respectively [262]. (d) SEM images of engineered hierarchical SHPS with micro-truncated cones and nanograss. (e) Anti-frosting performance of this hierarchical surface with activated edge effect at −10 °C. The red dotted circle highlights the icing area from the onset of icing (at time of 1410 s) to complete coverage (at time of 1805 s) [99]. (f) Schematic of edge shielding by covering the nanostructured sample with a Teflon gasket. (g) Top optical views of a nanostructured sample with edge shielding at the refrigerated time of 90 min in a controlled environment (temperature −10 °C, RH ~60%).
19. Figure 10.19 (a, b) Schematics of a liquid droplet placed on a textured surface impregnated with a lubricant, showing whether the droplet gets cloaked by the lubricant or not. (c) Schematics of the wetting configurations outside and underneath the droplet (column 1 and 2) for the latter case (b). There are six possible states (column 3) depending on how the lubricant wets the texture in the presence of air (the vertical axis) and water (horizontal axis).
20. Figure 10.20 (a) SEM images of as-fabricated circular mushroom post arrays, hierarchical silicon pyramid arrays, and CuO nanoblade decorated copper ball. (b1–3) Superhydrophobic-like bouncing breaks on oil-infused mushroom structure and pyramid arrays, while it takes place on liquid-infused spherical surface [272]. (c) Top-view SEM of a BMIm-impregnated surface with smooth microposts and (d) schematic of a condensed droplet on it. The post top is dry so that the condensed droplets can be in contact with the post top. (e) Condensed droplets appear to grow and coalesce while still remaining in the same location without significant movement. (f) Top-view SEM of impregnated surface with nanotextured microposts and (g) schematic of a droplet on it. The nanograss allows the lubricant to impregnate the post tops for reduced pinned fraction. (h) Obvious growth and motion of the condensed microdroplets.
21. Figure 10.21 (a, b) Images of frost formation on (a) bare Al and (b) SLIPS-Al substrates by deep freezing (−10 °C) in high-humidity condition (60% RH) and subsequent de-frosting by heating [108]. (c) Cross-sectional images showing the morphology of LIPS with an ~8-µm-thick excess oil film, (d, e) droplets before and after freezing on 10 µm-LIPS. (f) Schematics illustrating the oil migration, depletion, and ice penetration during condensation and freezing on LIPS.
22. Figure 10.22 (a) Profile image of a droplet on an SHPS at 1 min after the start of freezing. At the droplet edge (point of arrow), obvious meniscus can be seen. (b) Digitized profile evolution of a freezing droplet at different times. (c, d) The details of (c) meniscus extension 45 during formation process (at 2, 11, and 54 s) for evaporative freezing and subsequent (d) meniscus receding (at 20 min, 2 h, 5 h) for sublimation.
23. Figure 10.23 Schematics illustrating different force models and ice–substrate pairs for the different fracture styles and ice adhesion strengths. (a–e) Schematic illustrations of ice adhesion tests based on (a) shear force model using (b) a custom-built apparatus. (c) Fractured faces on non-icephobic (left) and icephobic (right) surfaces by shear force. For the icephobic surface, less ice scraps were left over [105]. The ice adhesion fracture mechanisms on the differently patterned substrates, like (d) post patterns and (e) cone patterns, are not the same. (f–j) Schematic illustrations of ice adhesion tests based on (f) normal force model II. This model has been employed by Davis et al. [302] by (g) an apparatus with pressurized air to push out the ice bulk. (h) The moment of accumulated ice being fractured by pressurized air as a normal force [302]. Compared to shear force, it is more likely to yield the same fracture style (adhesive fracture) both on (i) post- and (j) cone-patterned structures but different force areas, resulting in different ice adhesion.
24. Figure 10.24 (a) Effect of micropost density on the adhesion strength of ice on LIPS with silicone oil and DC704. (b) Schematic of the ice–DC704 LIPS and cross-section of the ice–LIPS interface. The red circle shows the stress concentrator and crack initiation site [310]. (c) Comparison of ice adhesion strength for a plain hydrophilic glass (SiO₂-OH), fluorosilanized flat glass (SiO₂-13 F), dry fluorosilanized inverse monolayer coating on glass (iMono13F), and the lubricated fluorosilanized inverse monolayer (iMono-SLIPS). (d) Schematics showing the construction of slippery lubricated and fluorosilanized inverse monolayer.
25. Figure 10.25 Fabrication features and icephobic performance of surfaces with self-lubricating liquid water layer (SLLWL). (a) Schematic illustration of the preparation of a surface with SLLWL by grafting the micro-porous silicon wafer arrays with cross-linked hygroscopic polymers, and its icephobic performance [112]. (b) Schematic illustration of the preparation of the anti-icing coating on various substrates by spin-coating. (c) Effectiveness of the icephobic coating with an aqueous lubricating layer, from which the formed ice could be blown off with a strong breeze. (d) Durability of the icephobic coating upon icing/deicing cycles. (e) Applicability and performance of the icephobic coating on various substrates.
26. Figure 10.26 (a) Schematic illustration of an icephobic polyelectrolyte brush layer with counter-ions Li⁺. (b) Icephobic performance of polyelectrolyte brush coating on glass compared to bare glass [118]. (c) Schematic illustration of the formation of icephobic coatings from UV-curable POSS-fluorinated methacrylate diblock copolymers. S13F and S17F denote the PMAPOSS-b-P13FMA-SH and PMAPOSS-b-P17FMA-SH containing surfaces.
27. Figure 10.27 Freezing-triggered spontaneous ice droplet launching from rigid SHPSs. (a–c) Image sequences showing water droplets solidifying on, and launching from, superhydrophobic surfaces in an environment at standard temperature with low-pressure and low-humidity conditions. The surfaces used were (a) silicon micropillar, and (b) etched aluminum. Micrographs of the two surfaces are given as the right insets. (c) Thermographic image sequences, which are synchronized with the above optical image sequence from side view.
28. Figure 10.28 Schematic illustrating static wetting models: (a) Young’s model; (b) Wenzel model; (c) Cassie–Baxter model, and (d) the dynamic de-wetting models on general surface and SHPSs.
29. Figure 10.29 (a) Sketch showing the competition between wetting pressure (P_wetting) and anti-wetting pressure (P_de-wetting) produced during impact on a pillar surface. (b–d) Schematics illustrating the three pressures (P_WH, P_D, and P_C) generated during the whole process and three possible wetting states during spreading.
30. Figure 10.30 (a) Sketch showing the interfacial energy transition during the coalescence of condensed microdroplet for self-jumping. (b) Diagram showing the relation between surface adhesion strength b and radius ratio of coalescing microdroplets and results of self-removal or no self-removal.
31. Figure 10.31 Schematic of the applications of anti-icing/icephobic materials with special wettability, which are expected to advance the development of interface science and bring new light to solve the atmospheric-icing-induced efficiency and safety problems.

List of Tables

Chapter 1: Introduction for Biomimetic Superhydrophobic Materials
1. Table 1.1 Corrosion characteristics on the surfaces of bare copper mesh, superhydrophobic PPy-coated copper mesh, bare stainless steel mesh, superhydrophobic PPy-coated stainless steel mesh.
Chapter 2: Superhydrophobic Surfaces from Nature and Beyond Nature
1. Table 2.1 Salvinia species depicting potential for removal of heavy metals [27, 164].
Chapter 9: Biomimetic Superhydrophobic Materials Applied for Oil/Water Separation (II)
1. Table 9.1 Acronyms, compositions, and proportions of various emulsions.
2. Table 9.2 Summary and comparison of various biomimetic thin membranes for oil/water emulsion separation.
Chapter 10: Biomimetic Superhydrophobic Materials Applied for Anti-icing/Frosting
1. Table 10.1 Summary and comparison of typical examples for various kinds of anti-icing/-frosting and icephobic materials.

Surfaces and Interfaces of Biomimetic Superhydrophobic Materials

Zhiguang Guo
Fuchao Yang

Authors

Professor Zhiguang Guo

Lanzhou Institute of Chemical Physics

State Key Laboratory of Solid Lubrication

730000 Lanzhou

China

and

Hubei Collaborative Innovation Centre

for Advanced Organic Chemical Materials

Hubei University

430062 Wuhan

China

Dr. Fuchao Yang

Hubei Collaborative Innovation Centre

for Advanced Organic Chemical Materials

Hubei University

430062 Wuhan

China

and

Lanzhou Institute of Chemical Physics

State Key Laboratory of Solid Lubrication

730000 Lanzhou

China

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