Differential superhydrophobicity and hydrophilicity on a thin cellulose layer

Here we have developed cellulosic materials (cotton fabric or paper) with differential superhydrophobicity and hydrophilicity on each side of the surfaces by coating with polyvinylidene fluoride and fluorinated silane molecules using electro-spraying. Such materials are advantageous in various textile and medical applications.Analysis of surface morphology indicated that, not only surface chemical property and roughness, but also particle diameter affects surface superhydrophobicity. Smaller particle diameter enhances superhydrophobicity, if the surface roughness and surface chemical property remain constant. By controlling these three factors, superhydrophobicity with a water contact angle of more than 160° can be achieved at one side of a thin cellulosic material while maintaining the hydrophilicity (contact angle is 0°) at the opposite side.     

Superhydrophobic electrosprayed PTFE

This paper shows the deposition of superhydrophobic PTFE (polytetrafluoroethylene) films on FTO (fluorine doped tin oxide) coated glass slides, employing the electrospray technique, using a commercial PTFE particle suspension in water. Water contact angles as high as 167° were measured on the PTFE surface. Water drop sliding angles at 2° show a very low contact angle hysteresis. Scanning electron and atomic force microscopy images show the typical rough micro/nanostructure required for superhydrophobicity.     

Different wetting behavior of alkyl- and fluorocarbon-terminated films based on cupric hydroxide nanorod quasi-arrays

Nanorods of cupric hydroxide (Cu(OH)₂) crystals with a diameter of about 100–500 nm and length of about tens of micrometers were directly fabricated on copper foils by alkali assistant surface oxidation technique. It was found that chemical modification with stearic acid (STA) or 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDES) led to significant increase in the contact angles of the Cu(OH)₂ nanorod quasi-array film, which could be related to the chemical modification and the roughened structure of the film surfaces. Compared with STA-modified surface, PDES-modified surface had a lower contact angle hysteresis (CAH) and adhesion for water droplets, possibly due to lower surface free energy of PDES than STA.     

Tailored surface properties of semi-fluorinated block copolymers by electrospinning

Diblock copolymers based on polystyrene (PS) macroinitiators and four different fluorinated monomers (perfluorooctyl ethyl methacrylate (FMA), pentafluorostyrene (FS), perfluorooctyl-ethylene oxymethyl styrene (EMS), 2,3,5,6-tetrafluoro-4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecaoxy)styrene (FSF)) were synthesized via atom transfer radical polymerization (ATRP). The lengths of the PS and fluorinated blocks were altered and the surface and self-assembling properties of the polymers were compared with respect to the fluorinated monomer used and the fluorine content. The surface properties, contact angles and surface tension, were enhanced by the existence of the CF₃ groups at the end of the alkyl chains compared with poly(pentafluorostyrene). Hydrophobicity of the surfaces was further enhanced by electrospinning the polymer solutions, which yielded superhydrophobic surfaces with water contact angles >150° for polymers having CF₃ groups.