A brief description of how superhydrophobicity can help mitigate the ice accretion problem on power network equipment and other exposed structures by reducing ice-tosurface adhesion is presented. Basic models, namely the Wenzel and Cassie-Baxter models, accounting for the contact angle of water on solid surfaces relating to the influence of surface roughness on hydrophobicity are discussed. The results on superhydrophobic aluminum surfaces, superhydrophobic nanostructured silver thin films, superhydrophobic nanostructured zinc oxide as well as superhydrophobic nanofibres are also discussed. Some of the superhydrophobic surfaces were tested for ice adhesion and a reduced ice adhesion was obtained.

Various surface characterization techniques were used to study the modified surface chemistry of superhydrophobic aluminum alloy surfaces prepared by immersing the substrates in an aqueous solution containing sodium hydroxide and fluoroalkyl-silane (FAS-17) molecules. The creation of a rough micronanostructure on the treated surfaces was revealed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) confirmed the presence of low surface energy functional groups of fluorinated carbon on the superhydrophobic surfaces. IRRAS also revealed the presence of a large number of OH groups on the hydrophilic surfaces. A possible bonding mechanism of the FAS-17 molecules with the aluminum alloy surfaces has been suggested based on the IRRAS and XPS studies. The resulting surfaces demonstrated water contact angles as high as ∼166° and contact angle hystereses as low as ∼4.5°. A correlation between the contact angle, rms roughnesses, and the chemical nature of the surface has been elucidated.

Superhydrophobic coatings, inspired by nature, are an emerging technology. These water repellent coatings can be used as solutions for corrosion, biofouling and even water and air drag reduction applications. In this work, synthesis of monodispersive silica nanoparticles of ~120 nm diameter has been realized via Stöber process and further functionalized using fluoroalkylsilane (FAS-17) molecules to incorporate the fluorinated groups with the silica nanoparticles in an ethanolic solution. The synthesized fluorinated silica nanoparticles have been spin coated on flat aluminum alloy, silicon and glass substrates. Functionalization of silica nanoparticles with fluorinated groups has been confirmed by Fourier Transform Infrared spectroscopy (FTIR) by showing the presence of C-F and Si-O-Si bonds. The water contact angles and surface roughness increase with the number of spin-coated thin films layers. The critical size of ~119 nm renders aluminum surface superhydrophobic with three layers of coating using as-prepared nanoparticle suspended solution. On the other hand, seven layers are required for a 50 vol.% diluted solution to achieve superhydrophobicity. In both the cases, water contact angles were more than 150°, contact angle hysteresis was less than 2° having a critical roughness value of ~0.700 µm. The fluorinated silica nanoparticle coated surfaces are also transparent and can be used as paint additives to obtain transparent coatings. OPEN ACCESSAppl. Sci. 2012, 2 454

:Monodispersive silica nanoparticles have been synthesized via the Stöber process and further functionalized by adding fluorinated groups using fluoroalkylsilane in an ethanolic solution. In this process, six different sizes of fluorinated silica nanoparticles of varying diameter from 40 to 300 nm are prepared and used to deposit thin films on aluminum alloy surfaces using spin coating processes. The functionalization of silica nanoparticles by fluorinated group has been confirmed by the presence C-F bonds along with Si-O-Si bonds in the thin films as analyzed by Fourier transform infrared spectroscopy (FTIR).The surface roughnesses as well as the water contact angles of the fluorinated silica nanoparticle containing thin films are found to be increased with the increase of the diameter of the synthesized fluorinated silica nanoparticles. The thin films prepared using the fluorinated silica nanoparticles having a critical size of 119 ± 12 nm provide a surface roughness of ∼0.697 µm rendering the surfaces superhydrophobic with a water contact angle of 151 ± 4°. The roughness as well as the water contact angle increases on the superhydrophobic thin films with further increase in the size of the fluorinated silica nanoparticles in the films.

Superhydrophobicity has been demonstrated on ultrathin rf-sputtered Teflon coated etched aluminum surfaces. The etching of aluminum surfaces has been performed using dilute hydrochloric acid. An optimized etching time of 2.5 min is found to be essential, before Teflon coating, to obtain a highest water contact angle of 164 ± 3° with a lowest contact angle hysteresis of 2.5 ± 1.5°, with the water drops simply rolling off these surfaces with even the slightest inclination of the sample. The presence of − CF3 radicals along with − CF2 radicals in the ultrathin rf-sputtered Teflon films, as investigated by X-ray photoelectron spectroscopy (XPS), contributes to the lowering of the surface energy on the aluminum surfaces. The presence of patterned microstructure as revealed by field emission scanning electron microscope (FESEM) together with the low surface energy ultrathin rf-sputtered Teflon films renders the aluminum surfaces highly superhydrophobic.