Superhydrophobic Particles Research Articles

Stellate superhydrophobic silver particles

Stellate silver particles, which have from 24 to 56 arms with a length of 30–40 μm, have been synthesized for the first time. The synthesis has been performed by the chemical reduction of an aqueous solution of silver nitrate by a urea alkaline solution under illumination at room temperature. Stellate Ag particles are hydrophobic and have the relative density lower than the density of water. Varying pH and the relation between the concentrations of reagents, one can obtain superhydrophobic powders and films consisting of stellate Ag particles with different lengths of arms.

Design and fabrication of robust, rapid self-healable, superamphiphobic coatings by a liquid-repellent “glue + particles” approach

The “glue+particles” approach has presented an excellent idea for promoting the practicability of superamiphiphobic surfaces. However, strong polar materials, such as epoxy and polyurethane, are usually employed as adhesives. The superamphiphobic behavior will be immediately lost when parts of superhydrophobic particles are removed. Thus, a glue with robust self-healing liquid-repellence is desirable, but remains challenging to realize. Herein, a robust, self-healable, superamphiphobic film was fabricated by a liquid-repellent “glue+particles” approach. The coating based on a sol-gel network showed exceptional liquid-repellency to low surface tension liquids including ethanol. The designed coating is based on robust sol-gel network dangling fluoroalkyl chains which integrates the bonding and self-healing mechanisms for providing a longer usage life. It could withstand at least 400cycles of abrasion under severe stress (45kPa), strong acid/base solution, hot-liquids and smudge treatment without apparently changing the superamphiphobicity. This novel and effective coating system may be useful for the development of robust protective clothing for various applications.

Concurrent Superhydrophobicity and Thermal Energy Storage of Microcapsule with Superior Thermal Stability and Durability

Despite considerable success in design and preparation of superhydrophobic particles, a facile and low-cost approach to develop multifunctional particles, especially microcapsules with the integrated performances of intrinsically long-lasting and highly stable superhydrophobicity and other passive/active functionalities, remains extremely challenging and is still in its infancy. Herein, we report a microcapsule (MC) with a micro/nano-hierarchical shell and a phase change material (PCM) core by a low-cost one-pot method. The resulting microcapsules (MCs) possess concurrent features of superhydrophobicity and thermal energy storage. Against thermal attack up to approximately 240 °C, the microstructure of MCs is nearly intact to avoid an obvious leakage of encapsulated PCM at high temperature, and meanwhile superhydrophobicity of MCs is enhanced unexpectedly to a static contact angle (CA) of 167.4 ± 0.3° and slide angle (SA) of 5 ± 0.5°. After conventional storage of 80 days, MCs still show a good superhydro...

Low cost and non-fluoride flowerlike superhydrophobic particles fabricated for both emulsions separation and dyes adsorption

Green fluoride-free superhydrophobic hierarchical flowerlike iron-containing MnO2 particles were synthesized by a simple one-pot approach and subsequently modified by stearic acid. The special selective wettability toward water and oil makes the particle can be used in oil-in-water emulsion separation. In addition, the particle also can be applied as absorption material to remove dyes which are serious water contaminants. More importantly, as for the mixture of emulsion and dye, the particles also have the ability to remove both oil and dye, making the particles potential for wastewater purification in the future.

Self-assembled and elastomeric arm decorated surfaces for high stress resistant super-repellent materials

Superhydrophobic (SH) particles and coatings with high mechanical resistance get widespread attention due to their versatile performance in applications such as self-cleaning, moisture protection and so on. In this work, superhydrophobic particles with excellent repellency to highly viscous and low surface tension liquids are synthesized via a two-step method. The grafting of soft and elastomeric polydimethyl siloxane segments onto silica surfaces confers the capacity for the absorption/distribution of mechanical impacts to SH particles. Thus, these particles can withstand high mechanical impact (∼8000 kg cm−2) and maintain a water contact angle (WCA) of around 150°. When SH particle incorporated PVDF-co-HFP is coated on substrates, the coating exhibits water roll-off properties with a sliding angle of 160°. This coating is tolerant to water hammer pressures of 1.33 MPa and sand impingement energies of 3.6 × 10−7 J per grain, and the coating restores SH properties under ambient conditions after these tests. Additionally, the surfaces damaged by impalement/impingement undergo self-reconstruction to hold their super-repellent nature. A fibrous and porous structure morphology is evident in field emission scanning electron microscope images which is attributed to the heat treatment and subsequent solvent evaporation process. Moreover, the coating displays super-repellency to different liquids and shows good adhesion on various substrates such as aluminium, polyimide, chloroprene rubber and stainless steel.

Durable Superhydrophobic Particles Mimicking Leafhopper Surface: Superoleophilicity and Very Low Surface Energy

The powder coating on brochosomes of leafhopper can repel water, diiodomethane (DM), and ethylene glycol (EG) droplets with contact angle >150°. This is attributed to the very low surface energy as low as <1.0 mN m–1 and their porous honeycomb structure. In this work, grafted silica nanoparticles with properties similar to leafhopper (LH) particle coating is synthesized in a single step by catalytic grafting of stearic acid on nonporous silica nanoparticles. The particles repel water, diiodomethane, and ethylene glycol with contact angle 167°, 161°, and 157°, respectively. The surface energy is also found as <1.0 mN m–1. The particle coating shows sliding angle <10° with these probe liquids. The superhydrophobic particles are resistant to pH = 1 to 13, boiling water conditions and preserves super-repelling nature to reference liquids after the treatments. In a mixture of hexane/water or kerosene/water, the particles completely wet the oleophilic part and repel water layer due to superoleophilic–superhydro...

Dopamine Polymerization in Liquid Marbles: A General Route to Janus Particle Synthesis.

Coating a liquid with a particle shell not only renders a droplet superhydrophobic but also isolates a well-confined microenvironment for miniaturized chemical processes. Previously, we have demonstrated that particles at the liquid marble interface provide an ideal platform for the site-selective modification of superhydrophobic particles. However, the need for a special chemical reaction limits their potential use for the fabrication of Janus particles with various properties. Herein, we combine the employment of liquid marbles as microreactors with the remarkable adhesive ability of polydopamine to develop a general route for the synthesis of Janus particles from micrometer-sized superhydrophobic particles. We demonstrate that dopamine polymerization and deposition inside liquid marbles could be used for the selective surface modification of microsized silica particles, resulting in the formation of Janus particles. Moreover, it is possible to manipulate the Janus balance of the particles via the addition of surfactants and/or organic solvents to tune the interfacial energy. More importantly, owing to the many functional groups in polydopamine, we show that versatile strategies could be introduced to use these partially polydopamine-coated silica particles as platforms for further modification, including nanoparticle immobilization, metal ion chelation and reduction, as well as for chemical reactions. Given the flexibility in the choice of cores and the modification strategies, this developed method is distinctive in its high universality, good controllability, and great practicability.

Superhydrophobic Particles Derived from Nature-Inspired Polyphenol Chemistry for Liquid Marble Formation and Oil Spills Treatment

Nature has given us great inspirations to fabricate high-performance materials with extremely exquisite structures. Presently, particles with a superhydrophobic surface are prepared through nature-inspired polyphenol chemistry. Briefly, adhering of a typical polyphenol (tannic acid, widely existed in tea, red wine, chocolate, etc.) is first conducted on titania particles to form a multifunctional coating, which is further in charge of reducing Ag+ into Ag nanoparticles/nanoclusters (NPs/NCs) and responsible for grafting 1H,1H,2H,2H-perfluorodecanethiol, thus forming a lotus-leaf-mimic surface structure. The chemical/topological structure and superhydrophobic property of the as-engineered surface are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), water contact angle measurements, and so on. On the basis of the hierarchical, superhydrophobic surface, the particles exhibit a fascinating capability to form liquid marble and sh...

Stimuli-Responsive Surfaces for Tunable and Reversible Control of Wettability.

Surfaces with controllable wettability can be fabricated by embedding superhydrophobic particles into stimuli-responsive hydrogels. When the hydrogel changes its size due to a specific stimulus, the wettability of the surface can be reversibly tuned from superhydrophobic to superhydrophilic. This general method is used to fabricate "smart" membranes for controlling the permeability of chemicals under the influence of multiple stimuli simultaneously.

Silica‐Based Liquid Marbles as Microreactors for the Silver Mirror Reaction

AbstractLittle attention has been paid to the participation of the shell of silica‐particle‐based liquid marbles and their influence on chemical reactions. The fabrication of liquid marbles with the encapsulating particle shells not only act as protecting layers to provide a confined environment, but also provide the reactive substrate surfaces to regulate the classical silver mirror reaction. Fabrication of silver mirrors with different morphologies was achieved by modifying particle surface properties, which could further lead to Janus liquid marbles. The different evaporation behavior of microreactors was demonstrated. Micrometer‐sized silica particles were used for the preparation of monolayer‐stabilized liquid marbles, which show great potential in fabricating Janus particles from superhydrophobic particles that are not attainable from Pickering emulsions.

Silica-based liquid marbles as microreactors for the silver mirror reaction.

Little attention has been paid to the participation of the shell of silica-particle-based liquid marbles and their influence on chemical reactions. The fabrication of liquid marbles with the encapsulating particle shells not only act as protecting layers to provide a confined environment, but also provide the reactive substrate surfaces to regulate the classical silver mirror reaction. Fabrication of silver mirrors with different morphologies was achieved by modifying particle surface properties, which could further lead to Janus liquid marbles. The different evaporation behavior of microreactors was demonstrated. Micrometer-sized silica particles were used for the preparation of monolayer-stabilized liquid marbles, which show great potential in fabricating Janus particles from superhydrophobic particles that are not attainable from Pickering emulsions.

Long-living, stress- and pH-tolerant superhydrophobic silica particles via fast and efficient urethane chemistry; facile preparation of self-recoverable SH coatings

A facile preparation of long-lived, stress- and pH-tolerant superhydrophobic (SH) particles is presented. The generated coatings are resistant to a wide pH range and display self-recoverable SH behavior after multiple tests.

Selective control of wetting on various substrates

Selective control of wetting is highly demanded for a broad window of applications. To selectively control wetting a surface should be locally modified by structuring surfaces or modulating surface chemistry. However, the local modifications are still challenging due to their complex and expensive processes. In this report we demonstrate the development of a facile approach for selective control of wetting on various substrates. Taking superhydrophobic polypropylene particles and hydrophilic silica nanoparticles, we here show that the locally controlled wetting can be achieved by coating the particles on a wide range of substrates including metal and paper and be applied to microfluidic channels. Furthermore, we represent that the coating method can be applied to any surfaces regardless of compositions and geometries.

Liquid marble granulation using super-hydrophobic powders

This work analyses the forces involved in liquid marble formation, primarily the surface energy of the powder on the liquid surface and the powder gravitational force, which we have shown to oppose liquid marble formation. In order to investigate these phenomena, hydrophobic powders possessing both high density and high contact angle need to be employed. For this purpose, superhydrophobic (SH) particles based on a copper substrate were prepared by a silver deposition technique of particle sizes 9, 20, 320 and 400μm having a contact angle with water approaching 160°. Liquid marbles formed using the SH copper substrate were compared with polymer powder (e.g., PMMA) based liquid marbles. Initially, the effective surface tension of the liquid marbles was determined using the maximal height methodology, which indicated that effective surface tension was a function of powder particle size. It is probable that the phenomena of heavy particles give rise to lower effective surface tension, is caused by the weight of the particles reducing the puddle height. Moreover, it was found that in cases with large dense SH powder particles, liquid marble formation was not possible, as the additional weight of the larger particles, lowered the “puddle” to an extent that marble became unstable and collapsed. Therefore, an analysis of the energies associated with the powder particles was undertaken to quantify the physical characteristics of powders that form liquid marbles under: (i) static and (ii) dynamic conditions. In addition, we have correlated this data using a regime map analysis in which we have plotted a surface energy versus a gravitational energy to provide operating regions within the regime map of potential liquid marble formation.

Combination of Bioinspiration: A General Route to Superhydrophobic Particles

We combine two amazing abilities found in nature: the superhydrophobic property of lotus leaf and the adhesive ability of mussel adhesive protein. The molecular structure mimic of the single units of adhesive proteins, dopamine, was polymerized in an alkaline aqueous solution to encapsulate microparticles. The as-formed thin polydopamine walls worked as reactive templates to generate silver nanoparticles on the capsuled particles. As a result, core/shell/satellite composite particles were generated with a hierarchical structure similar to the micromorphology of lotus leaf. The composite particles exhibited extremely water repellence after fluorination. Because dopamine can deposit and adhere to all kinds of materials, this method can be applied to diverse microparticles, from organic to inorganic. In addition, particles of different sizes and matters can be modified to superhydrophobic particles in one pot. Magnetic particles have also been prepared which could be used as oil-absorbent and magnetic controlled carriers. "Oil marbles" formed underwater were achieved for the first time.