Protocol for preparation of highly durable superhydrophobic bulks with hierarchical porous structures.

Superhydrophobic surfaces face challenges in comprehensive durability when used in extreme outdoor environments. Here, we present a protocol for preparing nanocomposite bulks with hierarchical structures using the template technique. We describe steps for using hybrid nanoparticles of polytetrafluoroethylene and multi-walled carbon nanotube to fill inside and dip on the polyurethane (PU) foam. We then detail procedures for its removal by sintering treatment. The extra accretion layer on the PU foam surface was highlighted to construct hierarchical porous structures. For complete details on the use and execution of this protocol, please refer to Wu et al.1.

Highly Efficient and Controlled Fabrication of Supraparticles by Leidenfrost Phenomenon.

Supraparticles (SPs) are agglomerates of smaller particles, which show promising applications in catalysis, sensing, and so forth. Preparation of SPs with controlled sizes, components, and structures in an efficient, scalable, and environmentally friendly way has become an urgent demand for the development of SPs. Herein, a method to fabricate SPs based on the Leidenfrost phenomenon is described. By dropping a nano-/microparticle dispersion on a metal plate at the Leidenfrost temperature (TLF) or higher, the solvent evaporates quickly, and SPs can be formed within 1 min. To understand the influence of various factors on the properties of SPs, and also to optimize the fabrication of SPs, the effects of metal surface roughness and primary particle concentration on TLF were carefully observed. Plates with a higher roughness as well as a higher primary particle concentration could trigger a lower TLF. Combining the regulation of composition and volume of the droplets, SPs with different sizes, compositions, and structures were precisely fabricated. Furthermore, highly porous titanium dioxide (TiO2) SPs with enhanced photocatalytic performance were fabricated via this method, showing the merits of the method in practical applications. This simple, efficient, and green method provides a new approach for controlled and large-scale fabrication of SPs with various functions.

Investigation of Commercial Iron Oxide Nanoparticles: Structural and Magnetic Property Characterization.

Magnetic nanoparticles (MNPs) have been extensively used as tiny heating sources in magnetic hyperthermia therapy, contrast agents in magnetic resonance imaging, tracers in magnetic particle imaging, carriers for drug/gene delivery, etc. There have emerged many MNP/microbead suppliers since the past decade, such as Ocean NanoTech, Nanoprobes, US Research Nanomaterials, Miltenyi Biotec, micromod Partikeltechnologie GmbH, nanoComposix, and so forth. In this paper, we report the physical and magnetic characterizations on iron oxide nanoparticle products from Ocean NanoTech. Standard characterization tools such as vibrating-sample magnetometry, X-ray diffraction, dynamic light scattering, transmission electron microscopy, and zeta potential analysis are used to provide MNP customers and researchers with an overview of these iron oxide nanoparticle products. In addition, the dynamic magnetic responses of these iron oxide nanoparticles in aqueous solutions are investigated under low- and high-frequency alternating magnetic fields, giving a standardized operating procedure for characterizing the MNPs from Ocean NanoTech, thereby yielding the best of MNPs for different applications.

A superhydrophobic coating harvesting mechanical robustness, passive anti-icing and active de-icing performances.

HYPOTHESIS: Ice accretion is a challenging issue for various residential activities and industrial facilities. However, most of the current anti/de-icing coatings fail to maintain their properties when subject to frequent mechanical wear, and their limited functionality (either anti-icing or de-icing individually) cannot meet the requirement of all-weather utilization. EXPERIMENTS: Herein, a multifunctional superhydrophobic coating is prepared by compositing ferroferric oxide nanoparticles (Fe3O4 NPs) with fluorinated epoxy resin via an inverse infiltration process. The surface composition, morphology and wettability are systematically characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), laser scanning microscopy and contact angle tensiometer. The anti-icing and de-icing performances are evaluated by investigating the freezing delay and photothermal effect, respectively. FINDINGS: This coating shows outstanding water repellency (water contact angle up to 161.0°, sliding angle down to 1.4°) and can maintain superhydrophobicity within 400 cycles of tape peeling, 260 cycles of sandpaper abrasion or 25 cycles of sand impact. Besides, because the hydrophobic nano/micro hierarchical structures tremendously retard the heat transfer, the freezing process of water droplet on this coating can be apparently delayed by up to 35 min as compared to the uncoated substrate. Moreover, owing to the photothermal effect of the Fe3O4 NPs, the coating's surface temperature can be rapidly increased above 0 °C under infrared irradiation, which facilitates the ice melting on cold surfaces. Our work offers a versatile approach to address the icing problems in diverse weather conditions, which exhibits great prospects in various engineering applications.

Irregularly Shaped Iron Nitride Nanoparticles as a Potential Candidate for Biomedical Applications: From Synthesis to Characterization.

Magnetic nanoparticles (MNPs) have been extensively used in drug/gene delivery, hyperthermia therapy, magnetic particle imaging (MPI), magnetic resonance imaging (MRI), magnetic bioassays, and so forth. With proper surface chemical modifications, physicochemically stable and nontoxic MNPs are emerging contrast agents and tracers for in vivo MRI and MPI applications. Herein, we report the high magnetic moment, irregularly shaped γ'-Fe4N nanoparticles for enhanced hyperthermia therapy and T2 contrast agent for MRI application. The static and dynamic magnetic properties of γ'-Fe4N nanoparticles are characterized by a vibrating sample magnetometer (VSM) and a magnetic particle spectroscopy (MPS) system, respectively. Compared to the γ-Fe2O3 nanoparticles, γ'-Fe4N nanoparticles show at least three times higher saturation magnetization, which, as a result, gives rise to the stronger dynamic magnetic responses as proved in the MPS measurement results. In addition, γ'-Fe4N nanoparticles are functionalized with an oleic acid layer by a wet mechanical milling process. The morphologies of as-milled nanoparticles are characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and nanoparticle tracking analyzer (NTA). We report that with proper surface chemical modification and tuning on morphologies, γ'-Fe4N nanoparticles could be used as tiny heating sources for hyperthermia and contrast agents for MRI applications with minimum dose.

Advances in Magnetoresistive Biosensors.

Magnetoresistance (MR) based biosensors are considered promising candidates for the detection of magnetic nanoparticles (MNPs) as biomarkers and the biomagnetic fields. MR biosensors have been widely used in the detection of proteins, DNAs, as well as the mapping of cardiovascular and brain signals. In this review, we firstly introduce three different MR devices from the fundamental perspectives, followed by the fabrication and surface modification of the MR sensors. The sensitivity of the MR sensors can be improved by optimizing the sensing geometry, engineering the magnetic bioassays on the sensor surface, and integrating the sensors with magnetic flux concentrators and microfluidic channels. Different kinds of MR-based bioassays are also introduced. Subsequently, the research on MR biosensors for the detection of protein biomarkers and genotyping is reviewed. As a more recent application, brain mapping based on MR sensors is summarized in a separate section with the discussion of both the potential benefits and challenges in this new field. Finally, the integration of MR biosensors with flexible substrates is reviewed, with the emphasis on the fabrication techniques to obtain highly shapeable devices while maintaining comparable performance to their rigid counterparts.

Molding processed multi-layered and multi-functional nanocomposites with high structural ability, electrical conductivity and durable superhydrophobicity.

Bioinspired superhydrophobic surfaces are mainly attributed to nano/micro textures and low surface energy materials, and have exciting potential for use in fields such as self-cleaning, water-proofing, anti-icing, anti-fouling, and so forth. However, the natural weakness of such delicate hierarchical surface structures pose great challenges to using artificial superhydrophobic surfaces under harsh mechanical conditions. Completely transforming multi-layered composite materials with good structural ability into superhydrophobic surfaces would greatly extend their durability under continuous mechanical abrasion. Endowing these composites with electrical conductivity could further expand their scope of application, especially in anti-static environments. Here we employ a facile molding process to fabricate a new type of multi-layered and multi-functional nanocomposite (MMNC), with a tensile strength up to ∼226.4 MPa, a modulus of up to ∼24.8 GPa, a surface electric conductivity of ∼1.2 S cm-1, a water contact angle of ∼155.4° and a water sliding angle of ∼2.0°. These multi-layered and multi-functional nanocomposites (MMNCs) demonstrate robust water-repellency under harsh mechanical abrasion (tested using a high tack sticky tape peel, cyclic sand paper abrasion and even file abrasion) and strong chemical corrosion (tested by using hydrochloric acid, sulfuric acid and sodium hydroxide solutions). Additionally, our MMNCs are highly resistant to water impalement (tested by turbulent water jet impact with a velocity of up to ∼29.5 m s-1 and a corresponding Weber number of ∼32 000). The robustness of the superhydrophobicity is multifaceted, and owing to the excellent structural performance and conductivity, these MMNCs could find potential uses in vehicles, containers, wind blades, infrastructures, electronics and so forth, which usually experience comprehensively harsh conditions such as rainfall, abrasion, static electricity, high loads and so forth.

All-organic superhydrophobic coatings with mechanochemical robustness and liquid impalement resistance.

Superhydrophobicity is a remarkable evolutionary adaption manifested by several natural surfaces. Artificial superhydrophobic coatings with good mechanical robustness, substrate adhesion and chemical robustness have been achieved separately. However, a simultaneous demonstration of these features along with resistance to liquid impalement via high-speed drop/jet impact is challenging. Here, we describe all-organic, flexible superhydrophobic nanocomposite coatings that demonstrate strong mechanical robustness under cyclic tape peels and Taber abrasion, sustain exposure to highly corrosive media, namely aqua regia and sodium hydroxide solutions, and can be applied to surfaces through scalable techniques such as spraying and brushing. In addition, the mechanical flexibility of our coatings enables impalement resistance to high-speed drops and turbulent jets at least up to ~35 m s-1 and a Weber number of ~43,000. With multifaceted robustness and scalability, these coatings should find potential usage in harsh chemical engineering as well as infrastructure, transport vehicles and communication equipment.