Electrophoretic-deposited Superhydrophobic Coatings

Electrophoretic deposition of MXenes and their composites: Toward a scalable approach

Over the past decade, MXenes, a novel class of advanced 2D nanomaterials, have manifested as a prominent electrode material with diverse applications. Their unique layered structures, negative zeta potential, charge carrier mobility, mechanical properties, adjustable bandgap, hydrophilicity, metallic nature, and surface chemistry collectively contribute to the abundance of active redox sites on the surface and a reduction in the ion diffusion pathway. Despite such promising attributes of MXene, challenges like aggregation and restacking reduce the accessibility of active surface sites for electrolyte ions. Amongst approaches such as surface functionalization, addition of spacers, or facilitating pore formation, the electrophoretic deposition (EPD) of MXene on substrates has commenced to gain attention aiming to mitigate these issues. More importantly, it offers large-scale film fabrication in a short time without the necessity of using a charge-inducing agent. This review compiles recent advances in the use of EPD for preparing MXene-based electrodes and discusses the effect of EPD parameters on the relevant device performance. Recognition is given to understanding the relation of MXene colloidal composition in aqueous (and in some cases, non-aqueous) dispersions, deposition times, and other relevant parameters on respective device performances. In conclusion, the potential avenues offered by MXenes for future research on electrode materials are emphasized.

Aqueous Cationic Fluorinated Polyurethane for Application in Novel UV-Curable Cathodic Electrodeposition Coatings

Aqueous polyurethane is an environmentally friendly, low-cost, high-performance resin with good abrasion resistance and strong adhesion. Cationic aqueous polyurethane is limited in cathodic electrophoretic coatings due to its complicated preparation process and its poor stability and single performance after emulsification and dispersion. The introduction of perfluoropolyether alcohol (PFPE-OH) and light curing technology can effectively improve the stability of aqueous polyurethane emulsions, and thus enhance the functionality of coating films. In this paper, a new UV-curable fluorinated polyurethane-based cathodic electrophoretic coating was prepared using cationic polyurethane as a precursor, introducing PFPE-OH capping, and grafting hydroxyethyl methacrylate (HEMA). The results showed that the presence of perfluoropolyether alcohol in the structure affected the variation of the moisture content of the paint film after flash evaporation. Based on the emulsion particle size and morphology tests, it can be assumed that the fluorinated cationic polyurethane emulsion is a core-shell structure with hydrophobic ends encapsulated in the polymer and hydrophilic ends on the outer surface. After abrasion testing and baking, the fluorine atoms of the coating were found to increase from 8.89% to 27.34%. The static contact angle of the coating to water was 104.6 ± 3°, and the water droplets rolled off without traces, indicating that the coating is hydrophobic. The coating has excellent thermal stability and tensile properties. The coating also passed the tests of impact resistance, flexibility, adhesion, and resistance to chemical corrosion in extreme environments. This study provides a new idea for the construction of a new and efficient cathodic electrophoretic coating system, and also provides more areas for the promotion of cationic polyurethane to practical applications.

Self-Healing of Biocompatible Superhydrophobic Coatings: The Interplay of the Size and Loading of Particles

The broad application potential of superhydrophobic coatings is limited by the usage of environment-threatening materials and poor durability. The nature-inspired design and fabrication of self-healing coatings is a promising approach for addressing these issues. In this study, we report a fluorine-free and biocompatible superhydrophobic coating that can be thermally healed after abrasion. The coating is composed of silica nanoparticles and carnauba wax, and the self-healing is based on surface enrichment of wax in analogy to the wax secretion in plant leaves. The coating not only exhibits fast self-healing, just in 1 min under moderate heating, but also displays increased water repellency and thermal stability after healing. The rapid self-healing ability of the coating is attributed to the relatively low melting point of carnauba wax and its migration to the surface of the hydrophilic silica nanoparticles. The dependence of self-healing on the size and loading of particles provides insights into the process. Furthermore, the coating exhibits high levels of biocompatibility where the viability of fibroblast L929 cells was ∼90%. The presented approach and insights provide valuable guidelines in the design and fabrication of self-healing superhydrophobic coatings.

Superhydrophobic 304 Stainless Steel Mesh for the Removal of High-Density Polyethylene Microplastics

Microplastics are a global issue that affects the environment, economy, as well as human health. Herein, we present a superhydrophobic 304 stainless steel mesh obtained by chemical etching followed by a liquid-phase deposition of lauric acid that can be used for microplastic removal. Field emission scanning electron microscopy (FE-SEM) and high-resolution X-ray photoelectron spectroscopy (HR-XPS), among other techniques, were used to identify the hierarchical structure and chemical composition of the surface. They revealed that iron laurate decreased the surface free energy. The 304 stainless steel mesh was superhydrophobic (169°) and superoleophilic (0°). Taking advantage of these wetting properties, we showed an innovative use of these superhydrophobic surfaces in the removal of microplastics. Additionally, we analyzed the removal efficiency from a surface and colloidal point of view that allowed us to explain and clarify why microplastics can also be removed by their wetting properties. The loss of a double electrostatic cloud between the microplastics and the predominance of van der Waals interactions in the organic phase promote the removal of these persistent pollutants from water.

Improving thermal conductivities of textile materials by nanohybrid approaches

The thermal transfer between individual body and the surroundings occurs by several paths such as radiation, evaporation, conduction, and convection. Thermal management is related with the heat transfer between the human body and the surroundings, which aims to keep the body temperature in the comfort range either via preserving or via emitting the body heat. The essential duty of clothing is to contribute to the thermal balance of the human body by regulating the heat and moisture transfer. In the case of poorly controlled body heat, health problems such as hyperthermia and heatstroke along with environmental problems due to higher energy consumption can occur. Recently, research has been focused on advanced textiles with novel approaches on materials synthesis and structure design, which can provide thermal comfort together with energy saving. This review article focuses on the innovative strategies basically on the passive textile models for improved thermal conductivity. We will discuss both the fabrication techniques and the inclusion of carbon-based and boron-based fillers to form nano-hybrid textile solutions, which are used to improve the thermal conductivity of the materials.

Superhydrophobic Aluminium Surface to Enhance Corrosion Resistance and Obtain Self-Cleaning and Anti-Icing Ability

A facile environmentally acceptable surface roughening method using chemical etching in HCl/H₂O₂ followed by grafting with n-octyltrimethoxysilane (AS-8) and 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (FAS-8) was studied to fabricate a (super)hydrophobic aluminium surface. The ground aluminium surface after selected etching times (before and after grafting), was characterised using a contact profilometer, optical tensiometer, scanning electron microscope coupled with an energy-dispersive spectroscope and X-ray photoelectron spectroscope to evaluate surface roughness, wettability, surface morphology and composition. The durability of the grafted surface was tested using thermal and UV resistance tests. The corrosion properties were evaluated using potentiodynamic measurements and standard salts spray testing, ASTM B117-19. Finally, the self-cleaning and anti-icing abilities were assessed. The grafted aluminium surface with octyl- or perfluorooctyl silane reflected the highly hydrophobic (AS-8) and superhydrophobic behaviour (FAS-8). Moreover, the different behaviour of the octyl- or perfluorooctyl chain in the silane molecule on modified surface properties was also noticed because durability tests confirmed greater thermal, UV stability and corrosion resistance of FAS-8 compared to AS-8. The aluminium etched for 2 min and grafted with FAS-8 also demonstrated an excellent self-cleaning and anti-icing performance.

Durable Superhydrophobic Coating for Efficient Microplastic Removal

The pollution caused by microplastics around the world is an increasingly significant issue that has to be tackled with different methods and technologies. Here, we report a straightforward and rapid process combining electrodeposition and electrophoresis to produce a durable superhydrophobic coating on an aluminum substrate (UNS A91070) that has a static contact angle (153°), sliding angle (1°), and contact angle hysteresis (1°). Field emission scanning electron microscopy and high-resolution transmission electron microscopy showed the presence of a hierarchical structure with nanolayers that were 70 nm thick. The chemical composition was also analyzed using attenuated total reflectance-Fourier transform infrared spectroscopy and high-resolution X-ray photoelectron spectroscopy, which revealed that the hierarchical structure was composed of zinc laurate (Zn(C11H20COO)2) that decreased the surface free energy of the system. Moreover, the coating showed high durability against abrasion caused by the P1200 SiC paper due to the presence of TiO2 particles in the upper layers as well as the homogeneous chemical composition of the hierarchical structure. Finally, taking advantage of the superoleophilic properties of superhydrophobic surfaces, the ability of the coating to remove high-density polyethylene microplastics from water was studied.