Superhydrophobic Composite Films Produced on Various Substrates

Abstract

Hydrophilic silica (SiO2) nanoparticles were dispersed in solutions of poly(methyl methacrylate) (PMMA) and in solutions of a commercial poly(alkyl siloxane) (Rhodorsil 224), and the suspensions were sprayed on glass surfaces. The effect of the particle concentration on the hydrophobic character of PMMA-SiO2 and Rhodorsil-SiO2 films was investigated and showed the following: (i) Static contact angles (theta s), measured on surfaces that were prepared from dilute dispersions (particle concentration <1% w/v), increase rapidly with particle concentration and reach maximum values (154 and 164 degrees for PMMA-SiO2 and siloxane-SiO2, respectively). Further increases in particle concentration do not have any effect on theta s. (ii) The effect of particle concentration on the contact angle hysteresis (thetaAlpha - thetaR) is more complicated: as the particle concentration increases, we first notice an increase in hysteresis, which then decreases and finally becomes constant at elevated particle concentrations. The lowest thetaAlpha - thetaR values were 5 degrees for PMMA-SiO2 and 3 degrees for siloxane-SiO2, respectively. (iii) SEM and AFM images show that a two-length-scale hierarchical structure is formed on the surface of the superhydrophobic films. It is demonstrated that superhydrophobicity can be achieved using various hydrophilic nanoparticles (alumina and tin oxide nanoparticles were successfully tested) and that the substrate has almost no effect on the hydrophobic character of the applied coatings, which were produced on silicon, concrete, aluminum, silk, wood, marble, and of course glass. The results are discussed in light of Wenzel and Cassie-Baxter models.

New Consolidant-Hydrophobic Treatment by Combining SiO2 Composite and Fluorinated Alkoxysilane: Application on Decayed Biocalcareous Stone from an 18th Century Cathedral

“…By comparing CA values obtained in samples treated with UCA-T and UCA-TS, similar values are obtained, showing a slight increase for the gel containing silica nanoparticles. This can be related to the increase in roughness produced by particles in the surface of the stone [13,33]. Table S1 show water droplet static and dynamic contact angle (CA) values.…”

“…However, this change does not produce modifications in repellence behavior because the original topography of the stone surface is hardly modified by the coating (see Figure 4). Consequently, as the biocalcareous stone is a high porosity material composed of macropores with distance between roughness peaks in the micrometer range, and a significantly lower distance between roughness peaks in the nanometer range is required to produce a Cassie-Baxter regime [13,33,47]. The coating containing nanoparticles (UCA-TS) cannot produce a repellent surface on which the water droplets do not stick [48].…”

“…The coating containing nanoparticles (UCA-TS) cannot produce a repellent surface on which the water droplets do not stick [48]. These high pitch values promote a Wenzel surface [33,48]. In this scenario, water penetrates into the grooves and valleys of roughness, promoting a high adhesion [49].…”

Metal oxide thin films and nanostructures for self-cleaning applications: current status and future prospects

“…Hou and Wang [73] prepared superhydrophobic polystyrene/titania nanocomposites with superhydrophilic property under UV irradiation. It is postulated that for a particular combination of metal oxide-polymer film, the superhydrophobicity of the composite material is independent of type of the metal oxide used and substrate properties [74]. Sometimes during the photocatalytic process of TiO 2 , the polymer matrix is degraded.…”

UV-curable nanocasting technique to prepare bioinspired superhydrophobic organic-inorganic composite anticorrosion coatings

“…Numerous methods, including photolithography [6], plasma treatment [7], templates [8], chemical deposition [9], solgel processes [10], chemical vapor deposition (CVD) [11], casting, and chemical etching [12], have been utilized to fabricate superhydrophobic surfaces. Several studies have been reported on using polymers and polymer nanocomposites for various applications such as fabricating hydrophobic/superhydrophobic surfaces [13][14][15][16][17][18][19][20][21]. Therefore, development of hydrophobic/superhydrophobic polymers and polymer nanocomposites has become an interesting subject in materials science.…”