Condensation is a phase change phenomenon often encountered in nature, as well as used in industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance. Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of superhydrophobic surfaces with even higher droplet mobility and, in some cases, coalescence-induced droplet jumping. Here, we provide a review of new insights gained to tailor superhydrophobic surfaces for enhanced condensation heat transfer considering the role of surface structure, nucleation density, droplet morphology, and droplet dynamics. Furthermore, we identify challenges and new opportunities to advance these surfaces for broad implementation in thermofluidic systems.

Surface wettability has emerged as a powerful tool to influence phase change phenomena such as ice formation and steam condensation. Ice mitigation using passive coatings offers tremendous promise; however, there remain several fundamental, durability- and manufacturing-related challenges that need to be addressed to harness the benefits of these coatings. Challenges limiting industrial utilization of such coatings can be classified into three categories: fundamental (frost buildup, non-zero ice adhesion, bulk ice nucleation, variable icing conditions), durability-related (harsh environment resistance, liquid impact resistance, erosion, fatigue), and manufacturing-related (scalability, coating economics). The role of passive surfaces in enhancing condensation heat transfer is a potential game changer in power plant efficiency enhancement; however, the benefits of such coatings will only be realized when durability and manufacturing challenges have been fully addressed.

Microstructures and mechanical properties of the Mg–4Y–2.5Nd–0.6Zr (wt%) alloy in the as-cast, as-rolled, and rolled-T5 conditions have been investigated. Results showed that the as-cast sample mainly consisted of the α-Mg matrix, network-like Mg41Nd5 phase, and cuboid-shaped Mg24Y5 particles. For the as-rolled sample, the thermally stable Mg24Y5 particles located at both grain boundaries and matrix, and the average grain size was greatly refined to about 15 μm. Yield strength, ultimate tensile strength, and elongation of as-rolled samples were 290 MPa, 235 MPa, and 10%, respectively. They were enhanced by 48.7%, 56.7%, and 38.9% correspondingly compared with those of the as-cast sample. After isothermal aging at 250 °C for 4 h, the optimal mechanical properties can be obtained. Besides, the tensile strengths of as-rolled and rolled-T5 samples decreased gradually with a gradual increase of ductility from room temperature to 300 °C. Quasicleavage and cleavage fracture were the fracture patterns of as-rolled and rolled-T5 samples, respectively, at room temperature. For samples under the two conditions, fracture mode similarly changed with the increase of test temperatures, and ductile fracture can be observed at higher temperature.

Reusable thermal protection systems of reentry vehicles are adopted for temperatures ranging between 1000 and 2000 °C, when gas velocity and density are relatively low; they exploit the low thermal conductivity of their constituent materials. This paper presents a new class of light structural thermal protection systems comprised of a load bearing structure made of a macroporous reticulated SiSiC, filled with compacted short alumina/mullite fibers. Their manufacturing process is very simple and does not require special devices or ambient conditions. The produced hetoroporous heterogeneous ceramics showed high radiations shielding capabilities up to 2000 °C in vacuum. Even after repeated exposures at higher temperatures, a significant degradation of the SiSiC scaffold was not observed.

Surfaces that display liquid contact angles greater than 150° along with low contact angle hysteresis for liquids with both high and low surface tension values are known as superomniphobic surfaces. Such surfaces are of interest for a diverse array of applications, including self-cleaning surfaces, nonfouling surfaces, stain-free clothing, spill-resistant protective wear, drag reduction, and fingerprint-resistant surfaces. Recently, significant advances have been made in understanding the criteria required to design superomniphobic surfaces. In this article, we discuss the roles of surface energy, roughness, re-entrant texture, and hierarchical structure in fabricating superomniphobic surfaces. We also provide a review of different superomniphobic surfaces reported recently in the literature and emphasize the need for mechanical, chemical, and radiation durability of superomniphobic surfaces for practical applications. Finally, we conclude with a discussion of the unresolved challenges in developing durable superomniphobic surfaces that define the scope for further improvements in the field.

Buffer leakage in aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure transistors is recognized as an issue that has deleterious consequences on device performance for high-power, high-frequency transistors and has been related to the presence of uncharged threading screw dislocations. In this study, we demonstrate that measurements of buffer leakage in AlGaN/GaN heterostructures grown on bulk gallium nitride (GaN) substrates are consistent with a mechanism based on the concept of dislocations acting as quantum wires in series with unintentional silicon (Si) impurity incorporation at the bulk GaN substrate/GaN buffer interface. The number of electronic channels N deduced from the leakage data using Landauer’s formula for the quantum resistance of N electronic channels is consistent with the number of dislocations along the ohmic contact pads determined from panchromatic cathodoluminescence and x-ray diffraction measurements of the dislocation density. This mechanism is consistent with Shockley’s suggestion that dislocations can act as one-dimensional conductors due to the presence of edge states along the dislocation core.

Semicoherent interfaces containing discrete dislocations are more energetically favorable than those containing continuous distributions because of lower chemical energy. The classical Frank-Bilby theory provided a way to determine the interface Burgers vectors content but could not effectively predict the characteristics of discrete dislocations. Atomistic simulations provide insights into analyzing the characteristics of discrete dislocations but the analysis is often disturbed by the reaction of interface dislocations. By combining the classical Frank-Bilby theory and atomistic simulations, an atomically informed Frank-Bilby theory proposed in this work can overcome shortcomings in both the classic Frank-Bilby theory and atomistic simulations, and enable quantitative analysis of interface dislocations. The proposed method has been demonstrated via studying two typical dissimilar metallic interfaces. The results showed that Burgers vectors of interface dislocations can be well defined in a Commensurate/Coherent Dichromatic Pattern (CDP) and the Rotation CDP (RCDP) lattices. Most importantly, the CDP and RCDP lattices are not simply a geometric average of the two natural lattices, that is the lattice misfit and the relative twist take the nonequal partition of the misfit strain and the twist angle.