A novel and cost-effective method for fabrication of a durable superhydrophobic aluminum surface with self-cleaning properties

Fabrication and Characterization of Superhydrophobic Al-Based Surface Used for Finned-Tube Heat Exchangers

Enhancing the heat transfer performance of heat exchangers is one of the main methods to reduce energy consumption and carbon emissions in heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. Wettability modified surfaces developed gradually may help. This study aims to improve the performance of heat exchangers from the perspective of component materials. The facile and cost-effective fabrication method of superhydrophobic Al-based finned-tube heat exchangers with acid etching and stearic acid self-assembly was proposed and optimized in this study, so that the modified Al fins could achieve stronger wettability and durability. The effect of process parameters on the wettability of the Al fins was by response surface methodology (RSM) and variance analysis. Then, the modified fins were characterized by field-emission scanning electron microscopy (FE-SEM), 3D topography profiler, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The durability of the superhydrophobic fins was investigated by air exposure, corrosion resistance, and mechanical robustness experiments. The RSM and variance analysis demonstrated that a water contact angle (WCA) of 166.9° can be obtained with the etching time in 2 mol/L HCl solution of 10.5 min, the self-assembly time in the stearic acid ethanol solution of 48 h, and drying under 73.0 °C. The surface morphology showed suitable micro-nano structures with a mean roughness (Ra) of 467.58 nm and a maximum peak-to-valley vertical distance (Rt) of 4.095 μm. The chemical component demonstrated the self-assembly of an alkyl chain. The WCAs declined slightly in durability experiments, which showed the feasibility of the superhydrophobic heat exchangers under actual conditions.

Charged membranes based on spider silk-inspired nanofibers for comprehensive and continuous purification of wastewater

Creating a facile and efficient porous membrane for the comprehensive treatment of both insoluble and soluble pollutants from water is of great significance, yet remains challenging. Here, we present a facile strategy to prepare charged nanofibrous membranes assembled from spider silk-like humped SiO₂/polyamide 66 (PA66)/polyaniline (PANI) nanofibers by combing Plateau-Rayleigh instability-induced assembly andin situsynthesis. The obtained nanofibrous membranes possess micro/nanostructured surfaces with promising superhydrophilic and underwater superoleophobic property, which are attributed to the synergy of hierarchical roughness and hydrophilic matrix. Combined with the superwettability and the integrated property of submicron pore size, high porosity, and good pore interconnectivity, the membranes can separate various oil-in-water emulsions with a remarkable permeation flux of 5403 l m^-2h^-1and a high separation efficiency (total organic carbon content <5 mg l^-1). Moreover, attributed to the Laplace pressure difference and positive potential of the spindle-knotted nanofibers, the biomimetic nanofibrous membranes could remove the filter cake during separation. In addition, the membrane exhibits a remarkable adsorption-reduction capacity of hexavalent chromium. The synthesis of such attractive nanomaterials may provide new insights into the development of multifunctional separation materials for environmental applications.

Fabrication of a gradient hydrophobic surface with parallel ridges on pyrolytic carbon for artificial heart valves

Effective surface modification to endow pyrolytic carbon (PYC) with long-term anti-thrombotic performance is highly demanded. In this work, a gradient hydrophobic surface on PYC was prepared by creating parallel ridges via the combination of laser etching technology and surface fluorosilanization. Scanning electron microscopy (SEM) observation confirms that the gradient hydrophobic surface is composed of a bare PYC region and four regions of parallel ridges with varying distances. The gradient hydrophobic surface is stable in air, phosphate buffer solution (PBS), and flowing PBS. Additionally, the gradient hydrophobic surface on PYC shows spontaneous droplet motion and much lower flow resistance than bare PYC. Compared to bare PYC, the gradient hydrophobic surface on PYC exhibits better blood compatibility and anti-adhesion performance. The results presented in this paper confirm that creating a gradient hydrophobic surface is an effective way of achieving long-lasting anti-thrombosis property.

Mechanically stable superhydrophobic nanostructured aluminum mesh with reduced water surface friction

Superhydrophobic surfaces demonstrate significant characteristics which make them suitable for a wide variety of applications. In this study, we propose a facile, one-step, and cost-effective anodizing scheme using aluminum nitrate/stearic acid mixture solution to create a superhydrophobic surface on an aluminum mesh. The surface outperforms the surface anodized by the widely used oxalic acid solution in terms of superhydrophobicity and water-surface friction behavior. The proposed surface reduced the friction by 11% on average respective to the surface prepared by oxalic acid. The durability of the introduced superhydrophobic surface has also been investigated. The proposed surface retained its high water contact angle and showed higher hydrophobicity relative to the surface anodized by oxalic acid after ten abrasion cycles. This method and surface may be used for numerous applications due to its ease of fabrication, low cost, and excellent performance in energy-loss reduction.