Superhydrophobic (SHPo) surfaces can provide high condensation heat transfer due to facilitated droplet removal. However, such high performance has been limited to low supersaturation conditions due to surface flooding. Here, we quantify flooding resistance defined as the rate of increase in the fraction of water-filled cavities with respect to the supersaturation level. Based on the quantitative understanding of surface flooding, we suggest effective anti-flooding strategies through tailoring the nanoscale coating heterogeneity and structure length scale. Experimental verification is conducted using CuO nanostructures having different length scales combined with hydrophobic coatings with different nanoscale heterogeneities. The proposed antiflooding SHPo can provide a ∼130% enhanced average heat transfer coefficient with ∼14% larger supersaturation range for droplet jumping compared to a previous CuO SHPo. The proposed anti-flooding parameter and the scalable SHPo will help develop high-performance condensers for real-world applications operating in a wide range of supersaturation levels.

Recently, lubricant-impregnated surfaces (LIS) have emerged as a promising condenser surface by facilitating the removal of condensates from the surface. However, LIS has the critical limitation in that lubricant oil is depleted along with the removal of condensates. Such oil depletion is significantly aggravated under high condensation heat transfer. Here we propose a brushed LIS (BLIS) that can allow the application of LIS under high condensation heat transfer indefinitely by overcoming the previous oil depletion limit. In BLIS, a brush replenishes the depleted oil via physical contact with the rotational tube, while oil is continuously supplied to the brush by capillarity. In addition, BLIS helps enhance heat transfer performance with additional route to droplet removal by brush sweeping. By applying BLIS, we maintain the stable dropwise condensation mode for > 48 hours under high supersaturation levels along with up to 61% heat transfer enhancement compared to hydrophobic surfaces.

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features of components in these structures can engender a synergistic effect on the physicochemical properties of the entire structure and the outstanding properties of their constitutive building blocks. For example, inspired by the 3D hierarchical structure of the gecko's feet, which enables them to climb various textured surfaces, such as concrete and glass, surfaces with strong adhesion have been widely used. [3,4] In addition, the micro/nanoscale hierarchical structures inspired by the lotus plant, which impart self-cleaning properties, prevent the adhesion of rain on windows, antennas, and solar cells, thereby maintaining their performance in harsh environments. [5] Research on the micro/ nano hierarchical structures has facilitated their applications to chemical sensors, [6] fuel cells, [7] and self-cleaning systems [8] owing to their increased surface areas and roughness. In particular, micro/nano hierarchical structures are suitable for these applications because they bolster the advantages of micro-and nanostructures. Typically, microstructures can be used to adjust mechanical properties such as the hardness and elastic modulus. [9] Nanostructures also exhibit characteristics such as hydrophobicity and increased surface area. [10,11] Well-designed and adjustable micro/nano hierarchical structures can be applied to harvesting systems, such as triboelectric generators and water harvesting devices with high performance through controlled mechanical properties and increased surface area. [12,13] Therefore, it is essential to fabricate well-designed hierarchical structures that can be manufactured by means of a low-cost process for applications in engineering fields.Several methods have been suggested for manufacturing micro/nano hierarchical structures on surfaces, including semiconductor fabrication processes, [14] molding and imprinting, [15] chemical synthesis, [16] and etching. [17] In particular, various methods have been proposed for fine-tuning the geometric features at different levels with high precision. For example, Tian et al. proposed hierarchically ordered structures using an electrohydrodynamic structure formation method based on a prestructured polymer under an applied electric field. [18] Lin et al. proposed superhydrophobic surfaces based on hierarchical structures using two-photon polymerization. [19] These methods are effective for fabricating complex micro/nano hierarchical structures on flexible substrates. However, these Three-dimensional (3D) hierarchical structures have been explored for various applications owing to the synergistic effects of micro-and nanostructures. However, the development of spherical micro/nano hierarchical structures (S-HSs), which can be used as energy/water harvesting systems and sensing devices, remains challenging owing to the trade-off between structural complexity and fabrication difficulty. This paper presents a new strategy for facile, scalable S-HS fabrication using a thermal expansion of microspheres and nanopatterned structures. When a specific tem...

We introduce a thin (<200 nm) superhydrophobic cerium-oxide surface formed by a one-step wet chemical process to enhance the condensation heat-transfer performance with improved thermal stability compared to silane-treated surfaces. The developed cerium-oxide surface showed a superhydrophobic characteristic with a low (<5°) contact angle hysteresis because of the unique surface morphology and hydrophobicity of cerium oxide. The surface was successfully incorporated to popular engineering materials including copper, aluminum, and steel. Thermal stability of the surfaces was investigated by exposing them to hot (∼100 °C) steam conditions for 12 h. The introduced ceria surfaces could maintain active dropwise condensation after the thermal stability test, whereas silane-treated surfaces completely lost their hydrophobicity. The heat-transfer coefficient was calculated using the thermal network model incorporating the droplet size distribution and morphology obtained from the microscopic measurement. The analysis shows that the suggested cerium-oxide surfaces can provide approximately 2 times and 5 times higher heat-transfer coefficient before and after the thermal stability test, respectively, mainly because of the decrease in the thermal conduction resistance across droplets. The results indicate that the introduced nanostructured cerium-oxide surface is a promising condenser coating to enhance the droplet mobility and the resulting condensation heat-transfer performance for various thermal and environmental applications, especially those being exposed to hot steam conditions.