Abstract:Captive bubbles on a superhydrophobic (SH) surface have been shown to increase in volume via injection of air through the surrounding plastron. The experimental contact diameter against volume trends were found to follow that predicted by the Surface Evolver simulation generally but corresponded with the simulated data at contact angle (CA) = 158° when the volume was 20 μL but that at CA = 170° when the volume was increased to 180 μL. In this regime, there was a simultaneous outward movement of the contact lin… Show more
“…Dimensions Contact angles surface. This is consistent with the findings of Huynh et al which show that a captive bubble on a SHPo surface can grow via injection of air elsewhere on the surface into the plastron [24]. To further illustrate this phenomenon, visualization images for the SHPo-R* surface with the same micro-structure (w = 39.9 µm, F c = 0.79) are shown in Fig.…”
This work experimentally explores sub-boiling pool nucleation on micro-structured superhydrophobic surfaces. All surfaces tested were submerged in a 20 mm deep pool of water and heated from below to maintain a constant surface temperature, while the side walls of the pool were insulated, and the top was covered. Three thermocouples positioned in the pool obtain the average pool temperature. A heat flux sensor is placed directly beneath the surface to measure the heat flux supplied to the pool. Free convection heat transfer coefficients are obtained for the sub-boiling temperature range of 40-90 • C. Six surface types are studied: smooth hydrophilic, smooth hydrophobic, superhydrophobic with rib/cavity structures, superhydrophobic with rib/cavity structures and additional sparsely spaced ribs to close off the cavities, circular posts, and circular holes. It is found that structured superhydrophobic surfaces provide cavities for nucleation to occur. More dissolved air effervesces from the water as the surface temperature increases due to an increased level of supersaturation and convection. The nucleation leads to large air bubble formations that reduce the overall convection coefficient when compared to the smooth surfaces. For the rib/cavity structured surfaces, the bubbles form in an anisotropic manner and are aligned with the surface structure. More bubbles are observed on the superhydrophobic surfaces where the cavities are bounded. Since water's ability to dissolve air is dependent on temperature, heat and mass transfer cannot be treated independently on any of the superhydrophobic surfaces studied here.
“…Dimensions Contact angles surface. This is consistent with the findings of Huynh et al which show that a captive bubble on a SHPo surface can grow via injection of air elsewhere on the surface into the plastron [24]. To further illustrate this phenomenon, visualization images for the SHPo-R* surface with the same micro-structure (w = 39.9 µm, F c = 0.79) are shown in Fig.…”
This work experimentally explores sub-boiling pool nucleation on micro-structured superhydrophobic surfaces. All surfaces tested were submerged in a 20 mm deep pool of water and heated from below to maintain a constant surface temperature, while the side walls of the pool were insulated, and the top was covered. Three thermocouples positioned in the pool obtain the average pool temperature. A heat flux sensor is placed directly beneath the surface to measure the heat flux supplied to the pool. Free convection heat transfer coefficients are obtained for the sub-boiling temperature range of 40-90 • C. Six surface types are studied: smooth hydrophilic, smooth hydrophobic, superhydrophobic with rib/cavity structures, superhydrophobic with rib/cavity structures and additional sparsely spaced ribs to close off the cavities, circular posts, and circular holes. It is found that structured superhydrophobic surfaces provide cavities for nucleation to occur. More dissolved air effervesces from the water as the surface temperature increases due to an increased level of supersaturation and convection. The nucleation leads to large air bubble formations that reduce the overall convection coefficient when compared to the smooth surfaces. For the rib/cavity structured surfaces, the bubbles form in an anisotropic manner and are aligned with the surface structure. More bubbles are observed on the superhydrophobic surfaces where the cavities are bounded. Since water's ability to dissolve air is dependent on temperature, heat and mass transfer cannot be treated independently on any of the superhydrophobic surfaces studied here.
“…A noteworthy feature of mode B is the loss of axisymmetry during the bubbling process, a phenomenon reported also by Huynh et al. (2015) for air plastrons. Figure 2.Quasi-static growth and dynamic detachment of an air bubble in still water, corresponding to experimental case 5 in table 1.…”
Section: Methodssupporting
confidence: 66%
“…These air micro-layers, also known as plastrons (Thorpe 1950;Flynn & Bush 2008), can be found in nature, with the self-cleaning property of lotus leaves as the prominent example (Marmur 2004;Cheng & Rodak 2005;Wang et al 2009). Although there are several bubble formation experiments conducted with superhydrophobic surfaces (Ling, Lu & Ng 2011;Huynh et al 2015), a systematic experimental and theoretical account of the maximum bubble base radius and its corresponding volume is still lacking, and constitutes the main objective of the present paper, where we experimentally perform the controlled inflation of a plastron until its stability limit is reached.…”
“…On the contrary, little impalement of water into the rough structures would ultimately trap air within the structures. In such a situation, an air bubble near the surface would immediately be imbibed into the rough structures, rendering them superaerophilic …”
Section: Theoretical Backgroundmentioning
confidence: 99%
“…The study elucidated the capability of contact line for progressively reducing the contact diameter when the volume of bubble reaches as high as 180 µL and the intuitive advancement while air was blown in. The possibility of using large air bubbles for fluid transport, its control, and automation were also advocated in the study …”
Section: Superaerophilicity and Superaerophobicitymentioning
In spite of large amount of research in fabricating surfaces of varying wettability by biomimicking the naturally occurring surfaces, the work on fundamentally and industrially important air bubble adhesion on solid surfaces and its applications are still in the burgeoning stage. The present progress report provides a discussion and a critical evaluation of the recent literature available on the fabrication of superaerophilic/superaerophobic surfaces via synergic modification of surface topography and surface chemistry. An abridge on the physics behind bubble wetting on a solid in a liquid medium is deciphered here, considering the interfacial surface tension balance at the three‐phase contact line, Laplace pressure, hydrostatic pressure, and surface forces, respectively. Emphasis is made on the advancement in micro/nanofabrication technologies to fabricate surfaces that break the conventional wisdom of complementary behavior of water and air bubble contact angles. The progress report presented here also shines light on the mechanism of air bubble dynamics on solid surfaces and the latest developments in achieving surfaces of varied air bubble adhesion and its applications. Finally, the prospects of the superaerophobic and superaerophilic surfaces in the near future together with the challenges faced in accomplishing them are also insinuated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
