Heterogeneous wetting

Wastewaters containing chlorinated hydrocarbons (CHCs) are very toxic for aquatic system even at concentrations of ppm levels [1] thus, appropriate treatment technologies are required for processing them to non-toxic or more biologically amenable intermediates. Catalytic wet oxidation can offer an alternative approach to remove a variety of such toxic organic materials in wet streams. Numerous supported catalysts have been applied for the removal of aqueous organic wastes via heterogeneous wet catalysis [1,2]. 

Applications of the heat of immersion technique to determinations of polarity of surfaces, site heterogeneities, wetting of surfactants, hydrophilicity, and the interaction of specific groups from solution with solids are on the increase. The technique is certain to provide new and valuable information about the solid-liquid interface in the near future. 

To comply with both criteria, wetting has to occur necessarily in the heterogeneous wetting state [8]. 

The CB contact angle cb which describes the most stable contact angle in the case of heterogeneous wetting is given by ... 

Superhydrophobic, characterisation, agarose, heterogenous wetting, sessile drop... 

Figure 10.5 (a) Homogeneous wetting according to Wenzel (b) heterogeneous wetting according to Cassie-Baxter [52],... 

Figure 12.6 shows a water droplet in a heterogeneous wetting state. The liquid in this state only contacts the top of the protrusions, leaving air trapped into the grooves [3]. This wetting state is called the Cassie-Baxter state. It is described by the following equation ... 

Figure 4.8 Schematics of a motion of the contact hne of a hquid droplet sitting on a solid surface, leading to a corresponding free energy variation for a smooth surface (Young model, a), complete penetration of the liquid into the recessed features of a pattern (Wenzel model, b), and for heterogeneous wetting regimes with absence of penetration (Cassie-Baxter model, c) and for partial penetration (d). In the Wenzel model, rfp = AB + BC + CD + DE)I AB + CD) according to the letters in (b). In the Cassie-Baxter model, (j) = (AB)I(AB + BE) according to the letters in (c).

In the heterogeneous wetting regime, air can instead be trapped inside the features underneath the liquid drop, which ideally stands on the top of the nanostructures. This situation (schematized in Figure 4.8c) is described by the Cassie-Baxter model. The free energy variation following the contact line displacement is ... 

Melnyk, O. and BouMierroub, R. (2008) Biomolecule and nanopartide transfer on patterned and heterogeneously wetted superhydrophobic silicon nanowire surfaces. Langmuir, 24(5), 1670-2. 

Galopin E, et al. Selective adhesion of bacillus cereus spores on heterogeneously wetted sUicon nanowires. Langmuir 2010 26(5) 3479-84. 

Cassie-Baxter-equation is suitable for apphcations where heterogeneous wetting is taking place (composite sohd/hquid-air interface) cos 6strm fsl cos 6jyt+ 1) — 1. 

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