Plasma treatment superhydrophobic surfaces

It has been demonstrated that the preparation of superhydrophobic polymer surfaces is possible by simple plasma surface modification, either in one or two-step processes. The O2 plasma induces a variable roughness while CF4 plasma increases the roughness and creates an apolar layer. By the two-step treatment, several plasma parameters were found which allowed the preparation of superhydrophobic surfaces with controlled roughness and chemical structure. It has been shown that a superhydrophobic surface can be obtained even with a low roughness, around 20 nm. 

Here we describe two simple fabrication processes to modify the surface of the device to achieve a very high water contact angle. In the first approach, the device was first coated with a thin film of hydrophobic materials, fluoropolymer in this case, and then oxygen plasma was used to create superhydrophobic surfaces. However, only in some cases, the chemical properties of the hydrophobic materials could be altered by the oxygen plasma treatment [19]. Therefore, a second technique has been developed where the nanostructures can be created on the device surfaces by a nanoimprint process [20]. Both of these approaches are compatible with the micro-fabrication process. 

Figure 1. Schematic for producing a superhydrophobic coating on device surfaces using oxygen plasma treatment, (a) The surface of the device is coated with a layer of fluoropolymer (Teflon), (b) Oxygen plasma treatment is used to roughen the surface of fluoropolymer. (c) A superhydrophobic surface is obtained after the oxygen plasma treatment.

In summary, we have developed two techniques to impart superhydrophobic property to the surfaces of devices. In the first approach, oxygen plasma treatment was used to roughen the Teflon coating whose surface water contact angle could be tuned form 120° to 168° by varying the oxygen plasma treatment time. However, the application of the oxygen plasma process is limited to fluoropolymers. In the second approach, nanoimprint process was used to create nanostructures on the... 

Fernandez-Blazquez,J.R, Fell, D., Bonaccurso, E., de Campo.A., 2011. Superhydrophilic and superhydrophobic nanostructured surfaces via plasma treatment.. Colloid Interface Sci. 357,234. 

Stability attributed to the presence of long and thin nanohairs on the fibers (Shin et al., 2012). In another example, inherent microstructure of cellulose paper was enhanced by plasma-assisted nanostructuring to create a surface that once coated with a thin fluorocarbon film was superhydrophobic (Balu et al., 2008).The nanotopography was varied with plasma treatment, yielding a surface in either the Wenzel or Cassie—Baxter states. 

X-ray photoelectron spectroscopy (XPS) analysis of a large number of samples which were treated under variations of the plasma parameters, i.e. process gas — e.g. C3HF7 or perfiuorocyclobutane (c—C4F8) —, mixture of plasma and carrier gas, and duration of the treatment, revealed that there was a correlation between the wettability and the surface content of carbon-bonded oxygen, i.e. C—O and C—OOR (Fig. 9). Depending on the process gas, the water repellence characterized by the DuPont grading could be increased from 2 up to 7 in the case of PET fabrics and from 3 to 6 in the case of fabrics made of PA (superhydrophobic samples would be characterized by a grading of 8). 

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