Wetting Transitions Experimental Data

Wetting transitions were observed under various experimental techniques utilizing a diversity of factors: gravity [101], pressure [61], bouncing of droplets [6, 56, 57, 76] evaporation of droplets [55, 70, 72], electric field in the electrowetting experiments [1, 2], and vibration of droplets [11, 16-18, 21, 22]. The interesting experimental technique allowing the study of an air layer responsible for the formation of the Cassie state was reported recently [88]. A superhydrophobic surface exposed to hydrostatic water pressure was irradiated by a laser beam. The jump in the reflectivity of the laser beam indicated the occurrence of WT.

Fig. 6.4 Wetting transitions observed by vibration of 15 il water drop deposited on the micrometrically rough PDMS surface. a The initial Cassie state. b The Cassie impregnating state induced by vibrations

Fig. 6.4 Wetting transitions observed by vibration of 15 il water drop deposited on the micrometrically rough PDMS surface. a The initial Cassie state. b The Cassie impregnating state induced by vibrations

The reflection interference contrast microscopy was used for the study of the air-water interface on the textured PDMS surfaces [72]. ESEM technique was used successfully for the study of WT during micro-droplet evaporation [76].

It should be mentioned that various experimental methods used for the investigation of WT supplied the close values of a pressure necessary for the Cassie-Wenzel transition, which is of the order of magnitude of 100-300 Pa for 10 il droplets deposited on micrometrically scaled rough surfaces [16, 17, 61]. It is noteworthy, that the Cassie air trapping wetting regime observed on natural objects (birds' wings) was much more stable when compared to that on artificial surfaces [21, 23]. Single and two-stage pathways of WT were observed, including Cassie (air-trapping)-Wenzel-Cassie (impregnating), Wenzel-Cassie (impregnating) and Cassie (air-trapping)-Cassie (impregnating) transitions [21, 23]. The lowest energy state corresponds to the Cassie impregnating wetting regime. Vibration-induced Cassie (air-trapping)-Cassie (impregnating) transition observed on (polydimethylsiloxane) PDMS substrate is illustrated in Fig. 6.4. The mechanisms of WT will be discussed in detail below.

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Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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