Size and morphology dependent surface wetting based on hydrocarbon functionalized nanoparticles

Hydrophobic polyethylene film prepared by film blowing process for preservation of fried shrimp rolls

Hydrophobic coatings have wide applications, but face challenges in food flexible packaging in terms of poor adhesion and inadequate wear resistance. Health hazards and poor adhesion drive the search for novel hydrophobic coatings substitutes. Here, we introduced rationally synthesized carnauba wax-SiO2 microspheres as a component to composite polyethylene (PE) film construction, and created a wear-resistant hydrophobic composite PE film via the blown film technique. The resultant hydrophobic composite film demonstrated an enhanced water contact angle from 86° to above 100°, coupled with favorable mechanical properties such as wear resistance, tensile strength and effective barrier performance against water vapor and oxygen. Upon implementation in the preservation of a Cantonese delicacy, Chaoshan fried shrimp rolls, it was observed that at 25 °C, the carnauba wax-SiO2-PE composite packaging film extended the shelf life of the product by 3 days compared to pure PE film.

Geometrically Amplified Wetting of Silver Nanosolder on a Rough Diamond Surface

The wetting behavior of silver at the nanoscale on a textured diamond substrate is not absolutely roughness-dependent in printing diamond chips, tough bioimplant coating, and joining for cutting tool industries. This study uses a molecular dynamics simulation to capture the stochastic wetting behavior toward precision for given geometries. It is deduced that the metalophilic character of molten silver is increased with an increase in roughness on sinusoidal contoured diamond substrates rather than orthogonal pillars of the same roughness until an equilibration time of 210 ps at a temperature of 950 K. Increasing the roughness after the equilibrium time causes a supermetalophilic angle of 13° for the sinusoid at 500 ps, and the orthogonal design causes the Wenzel state. Therefore, wetting states are metastable and ultimately depend upon the wetting time and geometry rather than the roughness only. A high joining strength creates a long-lasting coating, owing to the high surface energy of the textured surface. This study presents effective thin seam development in the least possible time of 230 ps and silver consumption at the nanoscale for supermetalophilic and metalophobic coatings in electronic packaging.

Cobalt-based MOF-derived carbon electrocatalysts with tunable architecture for enhanced oxygen evolution reaction

Development of the hydrogen economy requires the design of catalysts that increase the rate of the accompanying sluggish kinetic oxygen evolution reaction (OER). This is a key process in electrochemical energy conversion and storage, such as water splitting and metal-air batteries. The OER needs high overpotential and typically expensive precious metal-based catalysts. Therefore, designing low-cost and efficient electrocatalysts for OER is of paramount importance. In addition to focusing on the number of active sites or high specific surface area, the correlation between catalyst particle shape and performance should be considered. This work presents an electrocatalytic activity comparison of cobalt-containing carbons with different morphologies in the OER process. Employing metal-organic frameworks as carbon and metal precursors, the materials in the shape of polyhedrons, needles, unique spherical hedgehogs, and sea urchins were obtained. The effect of MOF template infiltration with additional carbon source on the physicochemical properties of electrocatalysts was also examined. The furfuryl alcohol-impregnated needle-shaped particles were characterized by a high content of cobalt active sites, surrounded by nitrogen-containing graphite layers. Electrochemical tests confirmed their best activity (overpotential 317 mV@10 mA/cm2), long stability (up to 20 h), as well as low reagents diffusion limitations (Tafel slope 57 mV/dec up to 24 mA/cm2). The vertically aligned structure of the catalyst contributed to improved detachment of the oxygen bubbles produced.

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.

Research progress on eco-friendly superhydrophobic materials in environment, energy and biology

In the past few years, bioinspired eco-friendly superhydrophobic materials (EFSMs) have made great breakthroughs, especially in the fields of environment, energy and biology, which have made remarkable contributions to the sustainable development of the natural environment. However, some potential challenges still exist, which urgently need to be systematically summarized to guide the future development of this field. Herein, in this review, initially, we discuss the five typical superhydrophobic models, namely, the Wenzel, Cassie, Wenzel-Cassie, "lotus", and "gecko" models. Then, the existence of superhydrophobic creatures in nature and artificial EFSMs are summarized. Then, we focus on the applications of EFSMs in the fields of environment (self-cleaning, wastewater purification, and membrane distillation), energy (solar evaporation, heat accumulation, and batteries), and biology (biosensors, biomedicine, antibacterial, and food packaging). Finally, the challenges and developments of eco-friendly superhydrophobic materials are highlighted.

Polarization effects on ablation efficiency and microstructure symmetricity in femtosecond laser processing of materials-developing a pattern generation model for laser scanning

This paper investigated the effects of femtosecond laser beam polarization on ablation efficiency and microstructure symmetricity for 64FeNi alloy (Invar) sheet processing to fabricate fine metal masks. It was found that the ablation efficiency for linear polarization was approximately 15% higher than that for circular polarization due to electric field enhancement induced by low-spatial-frequency laser-induced periodic surface structures (LIPSS). The hole size and sidewall taper angles for the microstructures generated by linear polarization were asymmetric, whereas those generated by circular polarization were symmetric due to non-oriented LIPSS. The asymmetric and symmetric three-dimensional microstructure profiles, measured by using a confocal laser scanning microscope, were verified by employing an analytical model that was derived using the total input fluence and the ablation rates for linear and circular polarizations, respectively.

Preparation of a superhydrophilic SiO2 nanoparticles coated chitosan-sodium phytate film by a simple ethanol soaking process

The development of environmentally friendly and transparent superhydrophilic food packaging materials is essential in our daily lives. The objective of this study was to develop a simple method of preparing a superhydrophilic, transparent, and biodegradable composite film. The composite film was obtained by soaking a chitosan-sodium phytate film in an ethanol solution of SiO₂ nanoparticles. The results showed that when the chitosan-sodium phytate film was coated with SiO₂ nanoparticles that were dissolved in 75% ethanol, its water contact angle (WCA) was reduced from 100° to 3°, and the film surface was changed from a hydrophobic to a superhydrophilic. Furthermore, the oxygen transmission rate (OTR) was significantly reduced, and the mechanical properties of the film were improved. The method is easy to carry out and can be used for the potential production of superhydrophilic materials.

Suppression of spallation induced nanoparticles by high repetition rate femtosecond laser pulses: realization of precise laser material processing with high throughput

This paper reports a mechanism to suppress nanoparticle (NP) generation during femtosecond laser processing of 64FeNi alloy (Invar) to realize high precision fine metal masks. Nanoparticle redeposition during processing can reduce precision and ablation efficiency. Since Gaussian laser beams have spatially distributed fluence, NP types can vary even within a laser spot. Surface areas irradiated by the beam center with high peak fluence can be decomposed into vapor and liquid droplets by phase explosion; whereas positions irradiated by the beam edge, where fluence is close to ablation threshold, can be decomposed by stress confinement under the surface, known as spallation. Spallation characteristics were verified from target surfaces covered with exfoliation and fragments. It occurred above a certain number of pulses, indicating a significant incubation effect. Spallation induced NPs, i.e., agglomerated fragments, distort micro-hole size and shape, but were effectively suppressed by increasing repetition rate, due to increased surface temperature, i.e., heat accumulation. Suppression also occurred from direct sample heating using a hot plate. Thus, thermal energy can relax stress confinement and inhibit spallation induced NPs. Numerical simulation for heat accumulation also confirmed that suppression arises from thermal effects. Increasing repetition rate also helped to increase productivity.

Comparison of hydrophobicity and durability of functionalized aluminium oxide nanoparticle coatings with magnetite nanoparticles-links between morphology and wettability

HYPOTHESIS

The wetting characteristics of coatings created using functionalised nanoparticles and adhesive resins, depends strongly on the particle distribution within the surface layers. Although it has been shown that commercially available adhesives improve the durability of hydrophobic nanoparticle coatings, the wettability of these surfaces is governed by the agglomeration behaviour of the particles within the adhesive. As a consequence of this, coatings where the particles are highly agglomerated within the adhesive show lower hydrophobicity.

EXPERIMENTS

The morphology and chemical composition of coatings formed from carboxylate functionalised Al₂O₃ and magnetite (Fe₃O₄) nanoparticles and epoxy resin on plastic was studied using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Water contact angle (WCA) measurements were used to investigate how the coatings' morphological characteristics and loading of the particles within the surface layers influenced their wettability. Infrared (IR) spectroscopy and thermogravimetric analysis (TGA) were used to study carboxylate adsorption onto the magnetite nanoparticles.

FINDINGS

Combining the Al₂O₃ nanoparticles with epoxy resin was observed to create highly hydrophobic coatings that displayed water contact angles (WCAs) between 145 and 150°. These coatings displayed good durability when sonicated in isopropanol and wiped with tissue. By comparison, coatings formed from the magnetite nanoparticles were substantially less hydrophobic and displayed WCAs between 75 and 125° when combined with epoxy resin. SEM revealed that the magnetite nanoparticles in the coatings were present as large agglomerates. By comparison, coatings formed from the Al₂O₃ nanoparticles showed a more homogenous particle distribution. Furthermore, XPS showed that the resin engulfed the magnetite nanoparticles to a far greater extent. The difference in wetting behaviour of these coatings is largely attributed to their different morphologies, since the particles are similar sizes and TGA shows that the particles possess similar carboxylate grafting densities. The uneven distribution of nanoparticles in the magnetite/epoxy resin coating is due to the particles' magnetic properties, which drive nanoparticle agglomeration as the coatings solidify. This work demonstrates that it is important to consider inter-particle interactions when fabricating low wettability composite coatings.