Electrochemical formation of porous copper 7, 7, 8, 8-tetracyanoquinodimethane and copper 2, 3, 5, 6-tetrafluoro-7, 7, 8, 8-tetracyanoquinodimethane honeycomb surfaces with superhydrophobic properties

The electrochemical formation of highly porous CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) and CuTCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) materials was undertaken via the spontaneous redox reaction between a porous copper template, created using a hydrogen bubbling template technique, and an acetonitrile solution containing TCNQ or TCNQF4. It was found that activation of the surface via vigorous hydrogen evolution that occurs during porous copper deposition and TCNQ mass transport being hindered through the porous network of the copper template influenced the growth of CuTCNQ and CuTCNQF4. This approach resulted in the fabrication of a honeycomb layered type structure where the internal walls consist of very fine crystalline needles or spikes. This combination of microscopic and nanoscopic roughness was found to be extremely beneficial for anti-wetting properties where superhydrophobic materials with contact angles as high as 177° were created. Given that CuTCNQ and CuTCNQF4 have shown potential as molecular based electronic materials in the area of switching and field emission, the creation of a surface that is moisture resistant may be of applied interest.

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites

Superhydrophobic amorphous carbon/carbon nanotube nanocomposites are fabricated by plasma immersion ion implantation with carbon nanotube forests as a template. The microstructure of the fabricated nanocomposites shows arrays of carbon nanotubes capped with amorphous carbon nanoparticles. Contact angle measurements show that both advancing and receding angles close to 180° can be achieved on the nanocomposites. The fabrication here does not require patterning of carbon nanotubes or deposition of conformal coatings with low surface energy, which are usually involved in conventional approaches for superhydrophobic surfaces. The relationship between the observed superhydrophobicity and the unique microstructure of the nanocomposites is discussed. © 2009 American Institute of Physics.

Electrowetting control of Cassie-to-Wenzel Transitions in superhydrophobic carbon nanotube-based nanocomposites

The possibility of effective control of the wetting properties of a nanostructured surface consisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated. By analyzing the electrowetting curves with an equivalent circuit model of the solid/liquid interface, the long-standing problem of control and monitoring of the transition between the "slippy" Cassie state and the "sticky" Wenzel states is resolved. The unique structural properties of the custom-designed nanocomposites with precisely tailored surface energy without using any commonly utilized low-surface-energy (e.g., polymer) conformal coatings enable easy identification of the occurrence of such transition from the optical contrast on the nanostructured surfaces. This approach to precise control of the wetting mode transitions is generic and has an outstanding potential to enable the stable superhydrophobic capability of nanostructured surfaces for numerous applications, such as low-friction microfluidics and self-cleaning.

Measurement studies on Superhydrophobic materials

Superhydrophobicity is directly related to the wettability of the surfaces. Cassie-Baxter state relating to geometrical configuration of solid surfaces is vital to achieving the Superhydrophobicity and to achieve Cassie-Baxter state the following two criteria need to be met: 1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures [1]. In this paper we discuss different measurements used to characterise/determine the superhydrophobic surfaces.

Superhydrophobic Polymers

Superhydrophobic polymers are particularly attractive materials, as they combine low cost, ease of processing, and compatibility with a variety of applications. Surfaces that display the Cassie–Baxter wetting state are particularly attractive for their self-cleaning properties. In this chapter, a brief overview of the wetting principles will be followed by an account of several techniques currently used to impart superhydrophobicity onto polymer surfaces. Surface roughness and surface structure will be the focus of this chapter, with an emphasis on topographies that exhibit microscale or nanoscale features arranged in hierarchical order.

Superhydrophobic fabrics for oil-water separation based on the metal organic charge transfer complex CuTCNAQ

This work reports on the fabrication of a superhydrophobic nylon textile based on the organic charge transfer complex CuTCNAQ (TCNAQ = 11,11,12,12-tetracyanoanthraquinodimethane). The nylon fabric that is metallized with copper undergoes a spontaneous chemical reaction with TCNAQ dissolved in acetonitrile to form nanorods of CuTCNAQ that are intertwined over the entire surface of the fabric. This creates the necessary micro and nanoscale roughness that is required for the Cassie-Baxter state thereby achieving a superhydrophobic/superoleophilic surface without the need for a fluorinated surface. The material is characterised with SEM, FT-IR and XPS spectroscopy and investigated for its ability to separate oil and water in two modes, namely under gravity and as an absorbent. It is found that the fabric can separate dichloromethane, olive oil and crude oil from water and in fact reduce the water content of the oil during the separation process. The fabric is reusable and tolerant to conditions such as seawater, hydrochloric acid and extensive time periods on the shelf. Given that CuTCNAQ is a copper based semiconductor may also open up the possibility of other applications in areas such as photocatalysis and antibacterial applications.

Effect of surface conditions on flow of a micropolar fluid driven by a porous stretching sheet

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Some surface profiles of a strip after plane-strain indentation by rigid bodies with serrated surfaces

This paper is concerned with the surface profiles of a strip after rigid bodies with serrated (saw-teeth) surfaces indent the strip and are subsequently removed. Plane-strain conditions are assumed. This has application in roughness transfer of final metal forming process. The effects of the semi-angle of the teeth, the depth of indentation and the friction on the contact surface on the profile are considered.