Silica sphere monolayers

We investigated the effect of PFDTS treatment on monolayer and multilayer arrays of silica microspheres with varying diameters. Details pertaining to the preparation methods and experimental conditions are available elsewhere [15]. In Figure 1 the formation of a homogeneous layer on silica sphere monolayers and the formation of nanostructures on... 

In their experiments the authors worked with gold-coated silica spheres, with self-assembled monolayers of mixtures of undecanethiols and co-hydroxy undecane thiols, to vaiy the contact angle between 20 and 100°. The results were compared with sessile drop measurements on the same system. A systematic difference up to 20° for the receding angles) between the two sets of results was observed, but since these differences depend on the nature of the solid surface it was not possible to pinpoint the origin definitely. A remarkable feature was that in the AFM method, hysteresis was very small, if not absent. Anyhow, this appears to be a promising technique. 

Fig. 2 Top-view SEM images of monolayer (left) en multilayer (right) silica sphere arrays after PFDTS assembly. The silica sphere diameters amount to 140 nm (top), 440 nm (middle) and 830 nm (bottom). The insets show side-view images of cleaved samples, as well as the large static contact angles (8/tl droplets) revealing the (super) hydrophobicity of the superstructures...

We have investigated the effect of PFDTS deposition on monolayer and multilayer arrays of silica spheres having different sizes. PFDTS deposition under ambient conditions... 

We constructed a simplified model for the monolayer of silica particles, shown in Fig. 2 The particles are assumed to be spherical and of uniform size and are arranged hexagonally at the air-water interface (the x,y-plane). The silica spheres are partially submerged in water. That means that the water-air interface is inside the layer h is the immersion depth. The particle diameter is d the distance between the particle centers is D. The layer thickness was assumed to be equal to the particle diameter. We also allowed partial coverage of the water surface by layer domains, i.e. the measured reflectance, Rm was assumed to be a combination of reflectance from the layer, R, and that from the bare substrate, Rs ... 

Fig. 7. Typical transmission electron micrographs of 640 nm polystyrene spheres on which one monolayer of Au Si02 nanoparticles has been assembled. The size of the Au cores is 15 nm in all cases. From left to right, the silica shell thicknesses are 8,18, and 28 nm...

Fig. 9. Normalized UV-visible spectra of dilute dispersions of 640 nm latex spheres coated with five monolayers of Au Si02 nanoparticles. The thickness of the corresponding silica shells is indicated. The trends are consistent with the predictions of Eq. (15) but quantitative agreement is not possible due to the higher volume fraction of the shells in experiments...

Based on colloidal monolayers of polystyrene spheres, we have prepared various two-dimensional nano-structured arrays by solution routes and electrodeposition. Many ordered structured arrays generated using these methods are of surface roughness on the nano- and micro-scales, and could be superhydrophobic or superhydrophilic. The nano-devices based on such nano-structured arrays would be waterproof and selfcleaning, in addition to their special device functions. In this article, taking silica, ZnO and gold as examples of the insulators, semiconductors and metals, respectively, we report some of our recent results to demonstrate controlled wettability and superhydrophobicity of two-dimensional ordered nano-stmctured arrays with centimeter square-size based on colloidal monolayers. 

Figure 5. Normalized UV-visible spectra of ersion of 640 run latex spheres coated with five monolayers of Au Si02 nanoparticles. The thickness of the corresponding silica shells is indicated.

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