Performance Of Superhydrophobic Surfaces Research Articles

Preparation and performance of superhydrophobic surfaces with low surface energy modified attapulgite

Material modification with low surface energy can offer lower surface free energy on micro- and nano-rough structures, which is necessary for developing superhydrophobic surfaces. Based on experiment and molecular simulation, the composite systems of attapulgite (APT) modified by alkylamine, alkylammonium salt and stearic acid were prepared. Combine surface free energy, electrostatic potential distribution, self-diffusion coefficient, and interfacial formation energy to favor the superhydrophobic composite system, and the interaction between low surface materials and attapulgite was explained. The results demonstrate that the hydrophobicity of APT are clearly modified by alkyl amine, alkyl ammonium salt, and stearic acid, and that when the molecular number of low surface energy monomers increases, the surface free energy of the composites first decreases and then increases. At the ideal concentration, the contact angles of alkyl amine/APT and SA/APT composites are all greater than 150°, and the antifouling performance is excellent. Finally, compounding technology was used to further optimize the superhydrophobic composite system. It was discovered that the hydrophobicity and antifouling properties of the composite system were superior to those of the monomer, and the octadecylamine/SA/APT composite system performed optimally at a contact angle of 167.54°.

Study on the mechanism of modified surface and magnetic nanofluids on cooling performance of wireless charging equipment under magnetic field

• A new coupled magnetic wireless charging heat transfer system is developed. • The thermo-hydraulic performance is analyzed by experiment and simulation. • A new idea of liquid flow model on superhydrophobic surface is proposed. • The entrance effect and heat transfer mechanism of boundary layer are analyzed. Recently emerged composite Fe 3 O 4 -CNTs/water nanofluids, serves as a new working medium with high controllability and special flow properties under magnetic field, which can be utilized for the energy saving and cooling of wireless charging equipment. Herein, we studied a cooling system with superhydrophobic (SHP) surface coupled with magnetic nanofluids. Experiments on convective heat transfer are carried out, and the performance of SHP surface is evaluated comprehensively. In addition, the influence of micro-groove, gas–liquid ratio and magnetic field intensity on the heat transfer performance of system is also studied through numerical simulations. Compared with the traditional forced convection cooling method, magnetic fluid on SHP surface destroys the thermal boundary layer under magnetic field, reduces the overall thermal resistance, and improves the heat exchange effect. Compared with water, magnetic fluid can increase the system temperature difference to 21.53%, meanwhile, the heat transfer efficiency of the whole cooling system can improve by 31.39%, under magnetic field. Furthermore, a new idea of flow model on SHP surface is also proposed in this work. Reported results illustrate an advanced cooling method realized via utilization of SHP surface with magnetic nanofluids and magnetic regulation.

Biphilic jumping-droplet condensation

Jumping-droplet condensation on rough superhydrophobic surfaces exhibits increased heat-transfer rates when compared with dropwise condensation on smooth hydrophobic surfaces. However, the performance of superhydrophobic surfaces is limited by the low individual droplet growth rates associated with their extreme apparent advancing contact angles. Here, we report that biphilic surfaces having smooth, low-surface-energy spots on a superhydrophobic background exhibit a 10× higher jumping-droplet condensation heat-transfer coefficient when compared with homogeneous superhydrophobic surfaces. Our detailed condensation heat-transfer modeling coupled with numerical simulations of binary and coordinated droplet coalescence show that spot wettability should not be optimized toward minimizing droplet nucleation energy barriers. Rather, spot wettability should be optimized to minimize droplet adhesion while maximizing individual droplet growth rates. Model-predicted design optimization of a variety of biphilic surfaces is validated against experiments. Our findings provide design guidelines for biphilic surface development to maximize condensation heat transfer.

Effect of Microstructure and Microscopic Condensation Behavior on the Anti-Frost Performance of Superhydrophobic Surfaces

Effect of Microstructure and Microscopic Condensation Behavior on the Anti-Frost Performance of Superhydrophobic Surfaces

Effect of Surface Structure Complexity on Interfacial Droplet Behavior of Superhydrophobic Titanium Surfaces for Robust Dropwise Condensation.

In general, the dropwise condensation supported by superhydrophobic surfaces results in enhanced heat transfer relative to condensation on normal surfaces. However, in supersaturated environments that exceed a certain supersaturation threshold, moisture penetrates the surface structures and results in attached condensation, which reduces the condensation heat transfer efficiency. Therefore, when designing superhydrophobic surfaces for condensers, the surface structure must be resistant to attached condensation in supersaturated conditions. The gap size and complexity of the micro/nanoscale surface structure are the main factors that can be controlled to maintain water repellency in supersaturated environments. In this study, the condensation heat exchange performance was characterized for three different superhydrophobic titanium surface structures via droplet behavior (DB) mapping to evaluate their suitability for power plant condensers. In addition, it was demonstrated that increasing the surface structure complexity increases the versatility of the titanium surfaces by extending the window for improved heat exchange performance. This study demonstrates the usefulness of DB mapping for evaluating the performance of superhydrophobic surfaces regarding their applicability for industrial condenser systems.

Improving the anti-icing performance of superhydrophobic surfaces by nucleation inhibitor

ABSTRACTTo investigate the effect of heterogeneous nucleation sites on the anti-icing performance of superhydrophobic surfaces, the superhydrophobic POSS/PDMS coatings were prepared and covered by PVA through spraying coating method. The surface morphology was characterized by SEM, and the anti-icing performance of surfaces was characterized through contact angle, freezing temperature of surface water droplet and ice adhesion. The results show that with the optimum match of the particle distance and PVA spraying times, the PVA-POSS/PDMS coating has better anti-icing performance than superhydrophobic POSS/PDMS coating: the freezing temperature of droplet on PVA-POSS/PDMS coating surface is −22.55°C, approximately 2°C lower than POSS/PDMS coating surface. This work confirms the adverse effect of heterogeneous nucleation sites and successfully improves the anti-icing performance of superhydrophobic surface by covering the heterogeneous nucleation sites with nucleation inhibitor. The synergism of nucleation inhibitor and the micro-nano structures is proposed, which will be conducive to the design of high-performance anti-icing materials.

Effect of surface topology on the wettability of superhydrophobic surfaces

In this paper, we develop a numerical model capable of predicting the apparent contact angle and the wetting state of liquid droplets on superhydrophobic surfaces using Surface Evolver. Specifically, our work investigates the effect of microscopic surface topology on contact angle and the state of wettability. Accordingly, surfaces with four different pillar geometries were investigated: square, cylindrical, parabolic, and conical. The performance of superhydrophobic surfaces was also tested for different solid-liquid material combinations. Our results reveal that cylindrical pillars prevent the transition from Cassie-Baxter to Wenzel wetting state at lower Young contact angles. Furthermore, superhydrophobic surfaces lose their repellency against organic liquids. Nonetheless, a surface with inverted conical pillars is both superhydrophobic and superoleophobic.