Fabrication of single-walled carbon nanotube (SWNT) networks using evaporation of SDS-SWNT sessile drops on a hydrophobized silicon substrate is reported. It is suggested that the organization of nanotubes during evaporation is controlled by aggregates (in the SDS-SWNT dispersion) and hydrophobicity of the substrate. On hydrophobic substrates, the evaporation of SDS-SWNT sessile drops proceeds through constant contact area. On hydrophilic substrates, nanotube aggregates in SDS-SWNT dispersion stop the contact line from moving, resulting in the formation of "coffee-stains". The (partial) removal of aggregates by centrifugation is essential for a freely moving contact line leading to the organization of nanotubes into a network of homogeneously distributed nanotubes on the most hydrophobic substrate. The evaporation of sessile drops was characterized by microscopic, spectroscopic, and topographical techniques.

-AbstractEnhancement of the surface properties of a material by means of laser radiation has been amply demonstrated previously. In this work a comparative study for the surface modification of nylon 6,6 has been conducted in order to vary the wettability characteristics using CO 2 and excimer lasers. This was done by producing 50 μm spaced (with depths between 1 and 10 μm) trench-like patterns using various laser parameters such as varying the laser power for the CO 2 laser and number of pulses for the excimer laser. Topographical changes were analysed using optical microscopy and white light interferometry which indicated that both laser systems can be implemented for modifying the topography of nylon 6,6.Variations in the surface chemistry were evaluated using energy-dispersive X-ray spectroscopy and x-ray photoelectron spectroscopy analysis and showed that the O 2 increased by up to 1.5% At. and decreased by up to 1.6% At. for the CO 2 and F 2 laser patterned samples, respectively. Modification of the wettability characteristics was quantified by measuring the advancing contact angle, which was found to increase in all instances for both laser systems. Emery paper roughened samples were also analysed in the same manner to determine that the topographical pattern played a major role in the wettability characteristics of nylon 6,6. From this, it is proposed that the increase in contact angle for the laser processed samples is due to a mixed intermediate state wetting regime owed to the periodic surface roughness brought about by the laser induced trench-like topographical patterns.Keywords: CO 2 laser, F 2 laser, nylon 6,6, wettability, contact angle. -IntroductionThe study of wettability has been a major focal point for many researchers and has been applied to a wide range of applications such as biomedical [1][2][3][4], coating technologies [5,6] and adhesion [7][8][9]. As the interface between a solid and liquid can be very complex it is necessary to account for the wetting regime that takes place. Two of the most common wetting regimes is that of Wenzel and Cassie-Baxter. In most instances it is seen that for hydrophilic surfaces (surfaces which provide contact angles of less than 90°) the Wenzel wetting regime dominates in which the whole of the liquid wets the surface. For hydrophobic surfaces (contact angles greater than 90°) the wetting regime tends to be that of Cassie-Baxter in which air-gaps are formed between the liquid-solid interface. However, in some cases it has been seen that it may be possible for a hydrophilic surface to give rise to some form of Cassie-Baxter wetting or CassieBaxter/Wenzel mixed intermediate wetting regime owed to the roughness and topographical pattern on the surface [10,11]. In this instance it is seen in some cases that increasing the surface roughness, through the patterning of a surface, can give rise to an increase in contact angle for hydrophilic materials. On the other hand, it has also been observed that in general, when the surface energy and its components are a ...

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