Static contact angles water

Figure 26.4 The effect of allowing a DI water droplet to equilibrate with a low energy (more hydrophobic) and a high energy (less hydrophobic) surface and ambient air on contact area, static contact angle, and droplet volume.

Substrate preparation. Thin films of mixed transition metal oxides were deposited by spin-coating on Si (100) tiles. Before deposition Si tiles were pretreated as follows. Square pieces (0.9 x 0.9 cm ) were first cleaned by HF (2%) dipping for 20 s to remove native oxide from its surface. After several rinsings with water (HPLC grade), the tiles were kept in water. UV/O3 treatment (Jelight s UVO-Cleaner A2, % = 254 nm) was applied to obtain a static contact angle nearing 0. 

Kamusewitz H, Possart W (1985) The static contact angle hysteresis obtained by different experiments for nthe system PTFE/water. Int J Adhes Adhes 5 211-215 Karpovich DS, Ray DJ (1998) Adsorption of dimethyl sulfoxide to the liquid/vapor interface of water and the thermochemistry of transport across the Interface. Phys Chem B 102 649-652 Kereszturi A, Jedlovszky P (2005) Computer simulation investigation of the water-benzene interface in a broad range of thermodynamic states from ambient to supercritical conditions. J Phys Chem B 109 16782-16793... 

The development of the photoresist was made by immersion in a solution of Su-8 developer for 6 min. The height of the photoresist was uniform at 50 pm. A hydrophobic monolayer of octadecyltrichlorosilane was finally deposited onto the mold. A 10 pL droplet was deposited on a glass wafer and placed with the mold in a desiccator for 1 h. The static contact angle with water droplet was about 110°. This last step produced a highly hydrophobic surface which was necessary for the PDMS pealing without damaging the Su-8 mold. 

Figure 4. Evolution of the air entrainment threshold velocity U as a fnnction of the static contact angle 0(, of the impacting spheres on a water-air interface. The sphere diameters are 25.4 mm ( ), 20 mm (v), 15 mm (O) and 7 mm (A). The dashed line, in the hydrophobic domain, is the theoretical evolution predicted by expression (6).

Figure 6. Zoomed-in chronophotographs of the impact region, when a hydrophobic sphere (static contact angle 6>q 115°) is falling on an air-water interface at different impact velocities compared with the air entrainment threshold f/ (a) U = 2.4 m/s < f/ and (b) U = 5.0 m/s > f/. The thin liquid film that develops and rises along the sphere in both cases either gathers at the pole to encapsulate the sphere (low velocity), or is ejected from the sphere thus creating an air cavity behind it (high velocity).

To characterise the test surfaces, standard static contact angle measurements were made with water at the temperature of 23°C in an atmosphere of 23°C and 50% rh. 

Static contact angles were determined separately by measuring the contact angle of 100 mm ( 2 mm ) drops of water and the solutions, respectively, that were placed on to a glass plate immersed in oil using a HVS microsyringe. 

For static contact angle measurements, errors occur because of size, evaporation, and creeping of the 2 / L water drop between deposition on the sample andmeasurement. The manual positioning... 

Stable, highly water-repellent surfaces (superhydrophobic) SH with a static contact angle with water of 150° and very low hysteresis were obtained with the alternation of nine layers constructing covalent LbL edifices with functionalized silica nanoparticles of different... 

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