Condensation Enhancement by Surface Porosity: Three-Stage Mechanism

Abstract

Surface defects, such as pores, cracks, and scratches, are naturally occurring and commonly found on solid surfaces. However, the mechanism by which such imperfections promote condensation has not been fully explored. In the current paper we thermodynamically analyze the ability of surface porosity to enhance condensation on a hydrophilic solid. We show that the presence of a surface-embedded pore brings about three distinct stages of condensation. The first is capillary condensation inside the pore until it is full. This provides an ideal hydrophilic surface for continuing the condensation. As a result, spontaneous condensation and wetting can be achieved at lower vapor pressure than on a smooth surface.

Controlled Self-Organized Positioning of Small Aggregates by Patterns of (Sub)nanosized Active Sites

“…The bottom-up approach to nanostructure formation at surfaces, , for instance, via localized precipitation, − scratch-induced graphoepitaxial growth, or nanoindentation templating is typically driven by (heterogeneous) nucleation and growth. , In the latter case “active” sites , may induce localized nucleation and growth through their specific chemical or topological properties, such as a pore (scratch, concavity). , Sites may be active for preferred nucleation through their specific chemical properties (a lower interfacial energy for the attached aggregates/particles) or due to their topological properties. A number of recent theoretical studies on the nucleation properties of single pores or grooves focus on the impact of geometry and size. ,− In fact, pores have for instance been proposed as effective means to increase the rate of (protein) nucleation. − The roughness of a surface has also been analyzed theoretically in some recent reports as a large assembly of nucleation active pores. − In strong contrast to a considerable number of theoretical investigations only rather few experimental data are available on this topic. ,− The reason is rather obvious, in particular, regarding individually reproducible observations on heterogeneous nucleation driven by singled out and locally identified, nanoscale topological artifacts. Such experimental investigations are rather challenging and thus scarce …”

Investigation of Dropwise Condensation on a Super-Aligned Carbon Nanotube Mesh-Coated Surface

“…Due to the resolution limitations of digital images, condensing droplets on these surfaces with diameters above 11.6 μm were counted and involved in Figure S4. For the SACNT mesh-coated surface, the number of condensing droplets first increased to the highest value (∼600–650 counts/mm 2 ) in 3 s. Then, the number of droplets sharply decreased to be about 300–350 counts/mm 2 due to the spontaneous coalescence of small droplets . The number of condensing droplets showed periodic fluctuations due to the sustaining condensation of vapor and spontaneous coalescence of small droplets.…”

“…For the SACNT meshcoated surface, the number of condensing droplets first increased to the highest value (∼600−650 counts/mm 2 ) in 3 s. Then, the number of droplets sharply decreased to be about 300−350 counts/mm 2 due to the spontaneous coalescence of small droplets. 48 The number of condensing droplets showed periodic fluctuations due to the sustaining condensation of vapor and spontaneous coalescence of small droplets. Although the droplets on the monolayer SACNT films and the SACNT groove surface showed the similar features, droplet densities were much lower than that on the SACNT mesh surface.…”

Isothermal Sulfur Condensation into Carbon Scaffolds: Improved Loading, Performance, and Scalability for Lithium–Sulfur Battery Cathodes

“…48 At the point of nucleation, the high radius of curvature at these sites leads to the preferential spontaneous nucleation of sulfur liquid on the cathode material in the smallest pore features due to the free-energy driven difference in chemical potential (μ) between the sulfur nuclei and the sulfur vapor (Figure 1). 49 After nucleation occurs, μ coating remains greater than than μ bulk , leading to a process where further mass accumulation occurs until reaching an equilibrium state where μ coating = μ bulk , and the process is complete. The final equilibrium state involves a carbon material where all surfaces are conformally coated with a layer of sulfur such that the surface free energy of the coated cathode and the surface free energy of the bulk liquid are similar.…”