Hydrophobic Powder Research Articles

FUNCTIONAL OPTICAL MATERIALS BASED ON AEROGELS

Sol-chemistry is an efficient physico-chemical method for the preparation of porous glassy or nanocrystalline materials with tailored electrical, thermal or optical properties. This paper focuses on the dependence preparation–structure-properties of hydrophobic silica aerogel granules, powders and composites with a potential application as optical materials. Using the technique of subcritical preparation of silica aerogel powders, multicolour emitting composites containing Eu(phen)2(NO3 )3 or Tb(phen)2(NO3 )3 nanocrystals are obtained and characterized with luminescence spectroscopy, quantum yield determination and texture measurements. A dependence of the luminescence quantum yield on the degree of hydrophobicity α of the silica aerogel powders is described.

Hydrophobic cement: Concept, preparation and application

Integral hydrophobic cement-based materials (CBMs) have traditionally been built by adding hydrophobic liquid solvents, hydrophobic solid powders, or admixtures modified by hydrophobic agents. In this work, we propose a new strategy to construct an integral hydrophobic CBMs based on direct hydrophobic cement. By ball milling, the 1.0 wt% stearic acid (SA) is adopted as modifier to prepare hydrophobic cement (SA1.0). SA1.0 process provides better dispersity in making CBMs. Hence, by using SA1.0 process, the CMB mechanical properties and durability can be improved. The mechanical and working performance of SA1.0 meet P·O 42.5 grade. Freeze-thaw resistance, sulfate resistance and electrochemical tests have demonstrated that CBMs prepared via SA1.0 process own excellent durability. Our findings provide new strategies for the formation of integral hydrophobic CBMs and a novel hydrophobic cementitious material for long-life CBMs.

Implementing a multi-cycle datapath with Liquid Marbles.

Liquid Marbles are liquid droplets encapsulated by hydrophobic powder particles; due to their non-wetting nature, they allow to manipulate liquids efficiently. Literature highlighted their potential to be employed as micro-reactors, micro-containers for growing micro-organisms and cells, micro-fluidics devices, and have also been used in the framework of unconventional computing. In this work, we discuss a theoretical implementation of all required components to define a multi-cycle datapath based on Liquid Marbles. Then, we consider issues related to scalability, by discussing how the circuits can be expanded with the growth of the inputs, and also how they can be modified to overcome the issues related to the growing time and space complexity.

Improving flow dynamics and storage longevity of a low-cost phosphorescent fingerprint powder.

An inexpensive, commercially available doped strontium aluminate phosphor with long-lived afterglow was prepared as a luminescent fingerprint dusting powder suited for challenging, highly patterned substrates; however, prolonged exposure to humidity was found to reduce that powder's affinity for fingermarks. Here, an enhanced preparation for synthesizing that fingerprint dusting powder is presented that prevents powder aggregation and loss of function upon exposure to humid environments. This was achieved by introducing a flow regulator during synthesis: hydrophobic silica SIPERNAT® D10 or SIPERNAT® D17. Increasing the hydrophobicity of the powder prevents aggregation by inhibiting the uptake of water, thereby improving the material's flow dynamics and transfer behavior from brush to fingermark. The angle of repose and flow characteristics made by the modified powders were quantified, with excellent affinity for fingermarks observed, even after being stored under 85% (±5%) humidity for 4 weeks. A preliminary comparison of the performance of the modified hydrophobic powders relative to the unmodified precursor revealed that more of the SIPERNAT® treated powder typically adhered to fingermarks while simultaneously imparting less background development. In addition, fewer clumps of particulate were observed in the developed fingermarks after addition of a hydrophobic flow regulator. This technical report outlines the updated method for synthesizing the fingerprint powder, with summarized flow performance results, and a demonstration of the modified powder's affinity for simulated fingermark evidence.

Preparation of hyperbranched hydrophobic nano-silica and its superior needling-effect in PDMS defoam agent

Hydrophobic nano silica powder is a kind of important synergist to silicone defoaming agents. The large pore volume and branched chain conformation of silica nanoparticles present superior effects on defoaming properties. However, silica nanoparticles synthesized by liquid phase easily aggregate and pore collapse because of their high surface activity and polarity, leading to poorer dispersity and limited practicability. In this paper, a novel hydrophobic silica with a hyperbranched structure was designed through in-situ modifying method with hexamethyldisilazane (HMDS) and polydimethylsiloxane (PDMS) in the liquid phase. The trimethylsilanol generated by HMDS hydrolysis reacts quickly with the highly active hydroxyl groups on the silica, causing the surface properties of the nanoparticles to transform from polar to non-polar properties. The steric hindrance of the trimethyl silicon and the reduction of the surface polarity effectively prevent silica pores from collapsing and maintain the macropore structures to realize the hyperbranched silica. At the same time, the −Si (CH3)2− from PDMS endowed the hyperbranched silica with excellent hydrophobicity. When applied in the defoaming agent, the hydrophobicity of silica contributes to dewetting the foams, and the hyperbranched spatial structures play an enhanced needling effect. Therefore, this hydrophobic hyperbranched silica exhibited a surprising defoaming effect, which significantly reduced the defoaming time from 464.4 s to less than 2 s, superior to commercial defoaming silica (155.3 s). The defoaming efficiency reached 100 % within 2 s of the end of the shaking, and the defoamer antifoaming ability was improved to reach 27.5 min, which was 77 % higher than that of commercial defoamer.

Study on physicochemical and anti-corrosion performance of methylsiloxane-based hydrophobic powder modified mortar

The porous hydrophilic nature of cement-based material is susceptible to water and corrosive media, severely reducing the durability. In this paper, methyl siloxane-based hydrophobic powder was prepared, and its effect on the physicochemical and anti-corrosion properties of mortar with different water-cement ratios were investigated. The results show that the addition of hydrophobic powder significantly improved the hydrophobic properties of mortars. Especially for the mortars with w/c ratios of 0.2 and 0.4, it showed superhydrophobicity with a water contact angle up to 156.5 ° and 152.3 ° respectively. Lower w/c ratio mortar has a denser microstructure, which reduces the water absorption rate of the mortar, and the hydrophobic powder enhances the hydrophobic effect of low w/c ratio mortar more significantly. The methyl siloxane groups in the hydrophobic powders will bind to the C-S-H gel in the mortar through Si-O bonding, preventing the C-S-H gel connections from forming a continuous network structure. This increased the pore volume and reduced the compressive strength by 14.6%-22.7%, but the total hydration degree was increased, and significant corrosion protection of the steel rebar was demonstrated.

Preparation of NaHCO3 fire extinguishing agent with perfluoropolyether groups to inhibit rapid re-ignition of Class B fires

To enhance the fire suppression effectiveness of dry powder extinguishing agents against Class B fires, the environmentally friendly surface modification of dry powder fire extinguishing agents using long-chain perfluoropolyether silanes (LCPS) was designed to modify the extinguishant. LCPS was synthesized by combining perfluoropolyether methyl ester (PME, Mw=4000 g/mol) and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (AAPS). A novel hydrophobic and oleophobic ultrafine dry powder fire extinguishing agent (LCPS-Na) was obtained by the introduction of LCPS into tetraethyl orthosilicate (TEOS)-modified ultrafine NaHCO3 powder (Na-UDP). The contact angles of water (WCA) and oil (OCA) on LCPS-Na are 151.4° and 145.8°, respectively. The hydrophobicity and oleophobicity of LCPS-Na are determined to be 94.2% and 85.6%, respectively. Moreover, the required concentrations of LCPS-Na powder to extinguish n-heptane and aviation kerosene fires are found to be 38.3 g/m3 and 39.7 g/m3, respectively, with a reduction of 31.6% and 31.0% compared to that of Na-UDP. The rekindling time for aviation kerosene after fire suppression was significantly prolonged to 40.6 s compared to Na-UDP (0.20 s), owing to the superior floating capability of LCPS-Na.

Liquid Marbles and Drops on Superhydrophobic Surfaces: Interfacial Aspects and Dynamics of Formation: A Review.

Liquid marbles (LMs) are droplets encapsulated with powders presenting varied roughness and wettability. These LMs have garnered a lot of attention due to their dual properties of leakage-free and quick transport on both solid and liquid surfaces. These droplets are in a Cassie-Baxter wetting state sitting on both roughness and air pockets existing between particles. They are also reminiscent of the state of a drop on a superhydrophobic (SH) surface. In this review, LMs and bare droplets on SH surfaces are comparatively investigated in terms of two aspects: interfacial and dynamical. LMs present a fascinating class of soft matter due to their superior interfacial activity and their remarkable stability. Inherently hydrophobic powders form stable LMs by simple rolling; however, particles with defined morphologies and chemistries contribute to the varied stability of LMs. The factors contributing to this interesting robustness with respect to bare droplets are then identified by tests of stability such as evaporation and compression. Next, the dynamics of the impact of a drop on a hydrophobic powder bed to form LMs is studied vis-à̀-vis that of drop impact on flat surfaces. The knowledge from drop impact phenomena on flat surfaces is used to build and complement insights to that of drop impact on powder surfaces. The maximum spread of the drop is empirically understood in terms of dimensionless numbers, and their drawbacks are highlighted. Various stages of drop impact-spreading, retraction and rebound, splashing, and final outcome-are systematically explored on both solid and hard surfaces. The implications of crater formation and energy dissipations are discussed in the case of granular beds. While the drop impact on solid surfaces is extensively reviewed, deep interpretation of the drop impact on granular surfaces needs to be improved. Additionally, the applications of each step in the sequence of drop impact phenomena on both substrates are also identified. Next, the criterion for the formation of peculiar jammed LMs was examined. Finally, the challenges and possible future perspectives are envisaged.

Berberine-loaded polylactic acid nanofiber scaffold as a drug delivery system: The relationship between chemical characteristics, drug-release behavior, and antibacterial efficiency.

Hydrophobic berberine powder (BBR) and hydrophilic BBR nanoparticles (BBR NPs) were loaded into an electrospun polylactic acid (PLA) nanofiber scaffold for modulating the release behavior of BBR in an aqueous medium. The BBR release from the BBR/PLA and BBR NPs/PLA nanofiber scaffolds was investigated in relation to their chemical characteristics, BBR dispersion into nanofibers, and wettability. The BBR release profiles strongly influenced the antibacterial efficiency of the scaffolds over time. When the BBR was loaded, the BBR/PLA nanofiber scaffold exhibited an extremely hydrophobic feature, causing a triphasic release profile in which only 9.8 wt % of the loaded BBR was released in the first 24 h. This resulted in a negligible inhibitory effect against methicillin-resistant Staphylococcus aureus bacteria. Meanwhile, the BBR NPs/PLA nanofiber scaffold had more wettability and higher concentration of BBR NPs dispersed on the surface of PLA nanofibers. This led to a sustained release of 75 wt % of the loaded BBR during the first 24 h, and consequently boosted the antibacterial effectiveness. Moreover, the cytotoxicity test revealed that the BBR NPs/PLA nanofiber scaffold did not induce any changes in morphology and proliferation of MA-104 cell monolayers. It suggests that the BBR/PLA and BBR NPs/PLA nanofiber scaffolds can be used in different biomedical applications, such as wound dressing, drug delivery systems, and tissue engineering, according to the requirement of BBR concentration for the desired therapeutic effects.

Effects of Enzyme Treatment and Carrier Agents on Chemical and Physical Properties of Almond Protein-Based Product

There has been an emerging trend towards the research of plant-based proteins over the past few years; however, there has been limited conductive observation of plant-based proteins from almond by-products, as well as the potential of using Flavourzyme and different carrier agents to obtain an instant protein-based powder. The purpose of this study was to investigate the effects of Flavourzyme at various concentrations (0, 0.5, 1, 1.5, 2, and 2.5%) and incubation times (30, 60, 90, 120, and 180 min), as well as carrier agents at different ratios with a 20% total concentration on the physicochemical properties of almond protein-based products using freeze-drying (FD). The results showed a higher protein content (p-value ≤ 0.05) using 1.5% Flavourzyme for 120 min compared to the other levels. There was no significant difference (p-value > 0.05) in the protein retention rate after freeze-drying of the samples. However, the addition of Maltodextrin (MA), Gum Arabic (GA), and Inulin (IN) encapsulants improved the physical and functional characteristics of freeze-dried almond protein-based powder (FDAP). However, the solubility of the powder is moderate. Water-holding-capacity (WHC) and Oil- Holding Capacity (OHC) are inversely proportional, where GA-coated powder is the most hydrophobic (17.72 ± 0.87 mL oil/g) and IN-encapsulated powder is the most hydrophilic (15.00 ± 0.87 mL water/g). In conclusion, IN could be a potential encapsulant for almond protein-based powder, because powder produced from IN or MA: IN is acceptable in terms of physical parameters, and IN can also enhance fiber content in the final product.

Enhancing flotation recovery of residual carbon from gasification waste by mixing hydrophobic powder with diesel as collector

Coal gasification fine slag (CGFS) is a solid waste containing residual carbon and ash generated during the coal gasification process, and the separation of the two components is the essential way to realize its environmental pollution reduction and resource value increase. Froth flotation is the preferred method for separating CGFS, but there is a barrier of low carbon recovery in this process due to the extensive adsorption of collector by the well-developed pores on residual carbon. In this study, a sufficiently simple yet innovative collector, a mixture of hydrophobic powder and diesel, was proposed in an attempt to break the bottleneck. Flotation experiments with common diesel and this novel collector were performed respectively, and FTIR, XPS, and SEM-EDX were employed to analyze the collector action mechanism. Flotation results revealed that the novel collector could significantly improve the residual carbon recovery; test results demonstrated that the novel collector could increase the hydrophobic functional group content on the fine slag surface, and the hydrophobic powders in this novel collector mainly appeared at the pore openings of the flotation concentrate. The essence of the mechanism is that the hydrophobic powders play a dual role of blocking pores and providing adsorption sites, thus facilitating the spreading of diesel on the carbon surface and promoting its floatability. The study can provide creative ideas for the efficient disposal of coal gasification waste.

Novel superhydrophobic energy-saving window coatings based on F–Nb–TiO2/SiO2 composites

Series of novel energy-saving window coatings based on F–Nb–TiO2/SiO2 nanocomposites with superhydrophobic self-cleaning performance were successfully prepared. Surface modification of F–Nb–TiO2 and SiO2 nanoparticles by aminopropyl triethoxy silane and perfluorooctyltriethoxysilane produced hydrophobic powders. With the help of the hierarchical structures of F–Nb–TiO2/SiO2 nanocomposites, superhydrophobic surfaces were obtained. The water contact angle of the composite coatings reached 155.6°. The prepared superhydrophobic coatings shown superior anti-fouling property and good mechanical performance. Furthermore, the composite coating can shield most of solar radiation. The composite coating lowed the air temperature of the simulate house by 11 °C in the outdoor thermal experiments. The integration of good solar filtration and exceptional anti-fouling performance makes F–Nb–TiO2/SiO2 coatings suitable candidates for energy-saving window coatings.

A two-step organic modification strategy for improving surface hydrophobicity of zeolites

The organic modification using a silane coupling agent can significantly improve the surface hydrophobicity of zeolite powders. However, insufficient hydroxyl group content on surface of the zeolites greatly limits the immobilization dosage of the agent, making the samples less hydrophobic. In this study, a two-step organic modification strategy using 1,2-bis(triethoxysilyl)ethane (BTESE) and dodecyltrimethoxysilane (DTMS) was adopted and developed to synthesize highly hydrophobic organic modified zeolite powders. The results showed that the BTESE modification could significantly increase the hydroxyl group content on the surface of zeolite powders, and relatively higher amount of DTMS could be then modified on the BTESE-modified samples. The mean critical surface tension, water vapor adsorption capacity, and water drop contact angle/penetration time of the 0.5% DTMS modified 10% BTESE-zeolite powders were 46.20 mN /m, 27 mg/g, and 142°/˃25 s, while those of the 0.5% DTMS modified zeolite powders were > 71.60 mN/m, 45 mg/g, and 124°/19.48 s, respectively, indicating that the sample synthesized by this two-step method was much more hydrophobic than the sample synthesized by traditional method. This two-step organic modification method appears to be a simple and effective way to prepare highly hydrophobic zeolite powders.

Waste Plastic Powder Coating on Acidic Aggregates: A New Hydrophobic Coating Technology to Build Moisture-Resistant Asphalt Mixtures

The surface energy of aggregate in asphalt pavements has a huge impact on its moisture susceptibility. The commercial antistripping agents widely used in asphalt may not be effective enough to enhance the moisture resistance if large quantities of acidic aggregates exist in pavements. This is also the reason why moisture damage is still an issue in many U.S. regions primarily supplied with “problematic” aggregates. In this regard, a promising solution is to use waste-plastic-coated aggregate, the surface of which is fundamentally modified and has a high affinity with asphalt because of the hydrophobic nature of plastic. However, it has not been widely promoted in the industry since there needs to be a practical and reliable method for uniform coating and avoiding the agglomeration of fine aggregate. To this end, an entirely new coating technology (thermoplastic polyethylene powder coating [TPPC]) was developed to coat aggregate using polyethylene (PE) powder. This technology utilizes a cheap but highly wettable fluidized bed to stably disperse the hydrophobic PE powder. Then, the dispersion liquid is sprayed onto the hot aggregate where the fluidized bed will evaporate fast while the PE particles stay, melt, and coat the aggregate surface. The microstructures of the coated aggregate were directly observed by scanning electron microscopy. Surface energy-based thermodynamic parameters were used to demonstrate the effect of TPPC on the moisture resistance of asphalt mixtures. This technology can be extended to other types of waste plastic if suitable fluidized beds are developed.

Universality of Scaling Laws Governing Contact and Spreading Time Spans of Bouncing Liquid Marbles and its Physical Origin.

The impact of liquid marbles coated with a diversity of hydrophobic powders with various solid substrates, including hydrophobic, hydrophilic, and superhydrophobic ones, was investigated. The contact time of the bouncing marbles was studied. Universal scaling behavior of the contact time tc as a function of the Weber number (We) was established; the scaling law tc = tc(We) was independent of the kind of powder and the type of solid substrate. The total contact time consists of spreading time and retraction time. It is weakly dependent on We and this is true for all kinds of studied powders and substrates. This observation hints to the surface tension/inertia spring model governing the impact. By contrast, the spreading time ts scales as [Formula: see text], n = 0.28 - 0.30 ± 0.002. We relate the origin of this scaling law to the viscous dissipation occurring within the spreading marbles. The retraction time tr grows weakly with the Weber number. The scaling law was changed at threshold values of We ≅ 15-20. It is reasonable to explain this change with the breaking of the Leidenfrost regime of spreading under high values of We.

Dispersion of hydrophobic waste amorphous carbon powder in cementitious environment and its effect on the permeability of cement paste

A Proper dispersion of powder-based hydrophobic admixtures in cementitious composites is challenging due to the presence of water. Studies have shown that amorphous carbon powder (ACP), a hydrophobic by-product of refining waste materials of paraffin production can be used as a hydrophobic agent. However, mixing methods and dispersing agents for modifying cementitious materials with ACP can significantly impact their mechanical properties, workability, water-repellency (hence the durability), and dispersion quality of ACP. Lack of information about the extent of their impact on different aspects mentioned above can hinder the practical use of ACP as a hydrophobic agent. To fill this gap, the objective of this study is to comprehensively investigate factors in the dispersion of ACP in cementitious materials and the tradeoff between mechanical properties and water permeability of ACP-modified cementitious materials when more than one mixing method is adopted. The impacts of different dispersing agents and mixing methods, including ultrasonication, dry mixing, and after mixing, on dispersion quality of ACP in cementitious environment analogous with aqueous solutions and hardened cement paste were assessed. Polycarboxylate ether-based superplasticizer (PCE) proved to be the most effective dispersing agent. Compressive strength of ACP modified cement paste can be increased or decreased with or without the workability reduction effect of ACP along with PCE respectively. Based on volume fraction of ACP clusters in X-ray micro-CT 3D reconstruction of hardened cement paste, ultrasonication was identified as the most effective mixing method and dry mixing was the worst in terms of achieving a uniform distribution of ACP in cement paste. However, all mixing methods presented more than 85% volume fraction of uniformly dispersed ACP areas with no major difference in terms of hydrophobic modification capability. Modifying cement paste with a higher amounts of ACP (5 to 15% by weight of cement) substantially increased water contact angle (up to 171% for w/c ratio of 0.35) and decreased water absorption. The hydrophobic modification capability of ACP increases with a decrease in the quality of cement paste and is diminished by the presence of PCE. Consequently, without PCE, water absorption rate was reduced by up to 92% in similar ACP modified cement paste samples, which also led to a major reduction in compressive strength.

Open millifluidics based on powder-encased channels

Millifluidics, the manipulation of liquid flow in millimeter-sized channels, has been a revolutionary concept in chemical processing and engineering. The solid channels that contain the liquids, though, are not flexible in their design and modification, and prevent contact with the external environment. All-liquid constructs, on the other hand, while flexible and open, are imbedded in a liquid environment. Here, we provide a route to circumvent these limitations by encasing the liquids in a hydrophobic powder in air that jams on the surface, containing and isolating flowing fluids, offering flexibility and adaptability in design, as manifest in the ability to reconfigure, graft, and segment the constructs. Along with the open nature of these powder-contained channels that allow arbitrary connections/disconnections and substance addition/extraction, numerous applications can be opened in the biological, chemical, and material arenas.

Production of small powder-stabilized droplets using superhydrophobic mesh

Massive production of tiny droplets is critical for industrial processes and biomedical applications. Such droplets are formed by splitting the bulk liquid (top-down) or condensation to grow the droplet (bottom-up). Various generation methods have been reported; however, the generated droplets stick to the contacting substrate and/or coalesce into a larger droplet, limiting handling flexibility and/or size uniformity. Herein, tiny powder-stabilized droplets were massively generated by applying pulse pressure to a “powdered” superhydrophobic mesh on a water pool. The generated droplets were stabilized by a fine hydrophobic powder, namely, liquid marble, which does not coalesce or stick to the contact materials. The effects of mesh size, wettability, powdering, and applied pressure on the droplet formation dynamics were investigated. The generated droplet size depended on the mesh size and droplets were not formed on the hydrophilic mesh. When the superhydrophobic mesh gradually sank into the water pool to apply quasi-static hydro-pressure, the penetrated water did not split, and a continuous large water droplet was formed. However, tapping the superhydrophobic mesh to apply pulsed hydro-pressure induced multiple droplets to split through the mesh penetration. Without powder, the formed droplets coalesced to form large droplets. However, when the superhydrophobic mesh was powdered, the formed droplets were coated with the hydrophobic powder to form a liquid marble, preventing their coalescence.

When marbles challenge pearls.

The spectacular nature of non-wetting drops mainly arises from their extreme mobility, and quick-silver, for instance, was named after this property. There are two ways to make water non-wetting, and they both rely on texture: either we can roughen a hydrophobic solid, which makes drops looking like pearls, or we can texture the liquid with a hydrophobic powder that "isolates" the resulting marble from its substrate. We observe, here, races between pearls and marbles, and report two effects: (1) the static adhesion of the two objects is different in nature, which we interpret as a consequence of the way they meet their substrates; (2) when they move, pearls are generally quicker than marbles, which might arise from the dissimilarity of the liquid/air interface between these two kinds of globules.

Facile preparation of monolithic superhydrophobic concrete with excellent anti-corrosion property

This work reports a monolithic superhydrophobic concrete with excellent corrosion resistance via mixing hydrophobic powder. The results showed that the monolithic superhydrophobic concrete exhibited a water contact angle (WCA) of 159°. More significantly, the corrosion resistance of the monolithic superhydrophobic concrete was greatly improved compared with that of ordinary concrete. We expect this kind of monolithic superhydrophobic concrete to be applied to various construction engineering for anti-corrosion.