Detection of Liquid Penetration of a Micropillar Surface Using the Quartz Crystal Microbalance

Abstract

A quantitative characterization of the wetting states of droplets on hydrophobic textured surfaces requires direct measurement of the liquid penetration into surface cavities, which is challenging. Here, the use of quartz crystal microbalance (QCM) technology is reported for the characterization of the liquid penetration depth on a micropillar-patterned surface. The actual liquid-air interface of the droplet was established by freezing the droplet and characterizing it using a cryogenically focused ion beam/scanning electron microscope (cryo FIB-SEM) technique. It was found that a direct correlation exists between the liquid penetration depth and the responses of the QCM. A very small frequency shift of the QCM (1.5%) was recorded when the droplet was in the Cassie state, whereas a significant frequency shift was observed when the wetting state changed to the Wenzel state (where full liquid penetration occurs). Furthermore, a transition from the Cassie to the Wenzel state can be captured by the QCM technique. An acoustic-structure-interaction based numerical model was developed to further understand the effect of penetration. The numerical model was validated by experimentally measured responses of micropillar-patterned QCMs. The results also show a nonlinear response of the QCM to the increasing liquid penetration depth. This research provides a solid foundation for utilizing QCM sensors for liquid penetration and surface wettability characterization.

Evaporation of ethanol/water mixture droplets on micro-patterned PDMS surfaces

“…Surfaces with microstructures such as micro-pillars and micropores have some applications in fabrication of superhydrophobic or superhydrophilic surfaces and oil/water inside the rocks [23][24][25][26][27][28][29]. Yuan et al [24,[30][31] elegantly studied the wettability of patterned surfaces.…”

Thermal Characterisation of Micro Flat Aluminium Heat Pipe Arrays by Varying Working Fluid and Inclination Angle

“…With the integration of inner ribs acting as fins, heat can spread from the upper surface to the bottom surface, as schematically shown in Figure 2. Thus, evaporation can be extended on all of the inner surface areas, which at least doubles the evaporating areas and can greatly enhance the overall heat transfer rate [34,35]. The configuration and working mechanism of a MF-AHPA are also schematically shown in Figure 1.…”

“…Thus, evaporation can be extended on all of the inner surface areas, which at least doubles the evaporating areas and can greatly enhance the overall heat transfer rate [34,35]. …”

Decoupling the influence of surface structure and intrinsic wettability on boiling heat transfer

“…These two factors are usually coupled together and are widely known as the Wenzel's effects. 15,16 Few experiments separated the effects of intrinsic wettability from surface morphology using smooth surfaces, such as flat surfaces 17 and Pt wires. 14 The intrinsic wettability can be altered by coating a thin hydrophobic or hydrophilic film, such as alkanethiol 17 or Teflon 18 for hydrophobicity, and SiO 2 18 or Al 2 O 3 14 for hydrophilicity.…”

“…6 The apparent contact angle on the ALD TiO 2 coated 2-layer meshes is nearly 0 , as predicted by the Wenzel's law. 16 The pool boiling experiments are conducted under steady-state conditions at atmospheric pressure using deionized water (see the supplementary material for the experimental system and data reduction). The surface structures, fabricated by sintering 2-layer and 4-layer copper meshes, are annotated as "2L" and "4L"; the intrinsic wettability, modified without/with a coating of ALD TiO 2 , are annotated as "Bare" and "TiO 2 ."…”