Tunable Surface Properties of Aluminum Oxide Nanoparticles from Highly Hydrophobic to Highly Hydrophilic

Investigation of Superhydrophobic and Anticorrosive Epoxy Films with Al2O3 Nanoparticles on Different Surfaces

In this study, superhydrophobic epoxy coatings were prepared on different surfaces by utilizing hydrophobized aluminum oxide (Al₂O₃) nanoparticles. The dispersions containing epoxy and inorganic nanoparticles with different contents were coated on glass, galvanized steel, and skin-passed galvanized steel substrates by the dip coating method. The contact angles of the obtained surfaces were measured via a contact angle meter device, and the surface morphologies were analyzed by utilizing scanning electron microscopy (SEM). The corrosion resistance was performed in the corrosion cabinet. The surfaces showed superhydrophobic properties with high contact angles greater than 150° and self-cleaning properties. SEM images indicated that the surface roughness increased as the concentration increased by the incorporation of Al₂O₃ nanoparticles into epoxy surfaces. The increase in surface roughness was supported by atomic force microscopy analysis on glass surfaces. It was determined that the corrosion resistance of the galvanized and skin-passed galvanized surfaces increased with the increase of Al₂O₃ nanoparticle concentration. It has been shown that red rust formation on skin-passed galvanized surfaces was reduced, although they have low corrosion resistance due to roughening on their surfaces.

Progress in Studies of Surface Nanotextures and Coatings with Nanomaterials on Glass for Anti-Dust Functionality

Dust pollution presents a wide range of adverse effects to product functionalities and the quality of human life. For instance, when dust particles deposit on solar photovoltaic panels, sunlight absorption is significantly reduced, and solar-to-electrical energy conversion yield may be lowered by 51%- Conventional (manual) dust removal methods are costly, consume significant material resources, and cause irreparable damage to the solar glass surface. Therefore, it is critical to develop glass surfaces that can clean themselves or are easily cleaned by natural forces. Many approaches have been attempted to reduce dust deposition, such as developing superhydrophobic surfaces and preparing anti-static surfaces. This paper reviews the recent progress in studies of anti-dust and cleaning mechanisms or methodologies, which include investigation into micro- and nano-sized dust properties, dust deposition processes and adhesion mechanisms to surfaces, and the state-of-the-art approaches to anti-dust and easy-cleaning functions that tailor surface micro-/nanotextures, lowering surface energy via nanocoatings, and enhancing anti-static properties with nanomaterials. We compare the advantages and disadvantages of various approaches and discuss the research prospects. We envision that future research will be focused on developing transparent surfaces with multiple dust-proof functions to cope with dust-burdening operating environments.

Interaction of Surface-Modified Alumina Nanoparticles and Surfactants at an Oil/Water Interface: A Neutron Reflectometry, Scattering, and Enhanced Oil Recovery Study

The evaluation of the mechanism of nanoparticle (NP)/surfactant complex adsorption at the critical oil/water interface was studied. A sophisticated technique (neutron reflectometry) was used to give a unique insight on NP/oil interactions in oil recovery systems. Herein, the adsorption of two modified alumina NPs with different degrees of hydrophobicity [hydrophilic = 2-[2-(2-methoxyethoxy)ethoxy]acetic acid and hydrophobic = octanoic acid (OCT)] stabilized with two different surfactants were studied at the oil/water interface. A thin layer of deuterated (D) and hydrogenated (H) hexadecane (contrast matching silicon substrate) oil was formed on a silicon block by a spin coating freeze process. The distribution of the NPs across the oil/water interface with the CTAB surfactant is similar between the two systems. NPs coated with CTAB have more affinity toward the oil/water interface, which explains the oil recovery increase by around 5% when flooding the core with the OCT-NP/CTAB system compared to the surfactant flooding alone. These results suggest that the NP/surfactant complexes can have potential usage in EOR recovery applications.

A novel ball-milled aluminum-carbon composite for enhanced adsorption and degradation of hexabromocyclododecane

Hexabromocyclododecane (HBCD) is one of the priority persistent organic pollutants (POPs), yet a cost-effective technology has been lacking for the removal and degradation of HBCD. Zero-valent aluminum (ZVAl) is an excellent electron donor. However, the inert and hydrophilic surface oxide layer impedes the release of the electrons from the core metallic Al, resulting in poor reactivity towards HBCD. In this research, a new type of modified mZVAl particles (AC@mZVAl^bm/NaCl) were prepared through ball milling mZVAl in the presence of activated carbon (AC) and NaCl, and tested for adsorption and reductive degradation of HBCD in water. AC@mZVAl^bm/NaCl was characterized with a metallic Al core with newly created reactive surface coated with a thin layer of crushed carbon nanoparticles. AC@mZVAl^bm/NaCl was able to rapidly (within 1 h) adsorb HBCD (C₀ = 2 mg L^-1) and thus effectively enriched HBCD on the carbon surface of AC@mZVAl^bm/NaCl. The pre-enriched HBCD was subsequently degraded by the electrons from the core Al, and ∼63.44% of the pre-sorbed HBCD was completely debrominated after 62 h of the contact. A notable time lag (∼12 h) from the onset of the adsorption to the debromination was observed, signifying the importance of the solid-phase mass transfer from the initially adsorbed AC particles to the reactive Al-AC interface. Overall, AC@mZVAl^bm/NaCl synergizes the adsorptive properties of AC and the high reactivity of metallic Al, and enables a novel two-step adsorption and reductive degradation process for treating HBCD or likely other POPs.

On the Colloidal Behavior of Cellulose Nanocrystals as a Hydrophobization Reagent for Mineral Particles

In the search for more sustainable alternatives to the chemical reagents currently used in froth flotation, the present work offers further insights into the behavior of functionalized cellulose nanocrystals as mineral hydrophobization agents. The study corroborates that hexylamine cellulose nanocrystals (HACs) are an efficient collector for the flotation of quartz and also identifies some particular characteristics as a result of their colloidal nature, as opposed to the water-soluble reagents conventionally used. To investigate the individual and collective effects of the frother and HACs on the attachment of particles and air bubbles, an automated contact timer apparatus was used. This induction timer measures particle-bubble attachment probabilities (P_att) without the influence of macroscopic factors present in typical flotation experiments. This allowed the study of the combined influence of nanocellulose and frother concentration on P_att for the first time. While HACs readily adsorb on quartz modifying its wettability, the presence of a frother leads to a drastic reduction in P_att up to 70%. The improved recovery of quartz in flotation cells might thus be attributed to froth stabilization by HACs, perhaps acting as a Pickering foam stabilizer. Among the main findings, a tendency of HACs to form mineral agglomerates was identified and further explained using the extended DLVO theory in combination with measured adsorption rates in a quartz crystal microbalance. Therefore, this study distinguishes for the first time the antagonistic effect of frothers on P_att and their synergies with HACs on the stabilization of orthokinetic froths through the hydrophobization mechanism unlike those of typical water-soluble collectors.

Shell-by-Shell Functionalization of Inorganic Nanoparticles

The current state of the hierarchical chemical functionalization of inorganic nanoparticles (NPs) by shell-by-shell (SbS)-assembly of organic layers around the NP cores is summarized. This supramolecular functionalization concept is based on two steps: 1) the covalent grafting of a first ligand-shell consisting of, for example, long chain phosphonic acids and 2) the noncovalent interdigitation of amphiphiles forming the second ligand shell. The latter process is guaranteed predominantly by solvophobic interactions. These highly order organic-inorganic hybrid architectures are currently an emerging field at the interface of synthetic chemistry, nanotechnology, and materials science. The doubly functionalized NPs display tunable materials properties, such a controlled dispersibility and stability in various solvents, highly efficient trapping of guest molecules in between the ligand shells (water cleaning) as well as compartmentalization and modification of electronic interactions between photoactive components integrated in such complex nano-architectures. Such SbS-functionalized NPs have a high potential as water-cleaning materials and also some first prototype applications as biomedicinal therapeutics have been presented.

Plasmonic Biosensing with Aluminum Thin Films under the Kretschmann Configuration

Aluminum has recently attracted considerable interest as a plasmonic material due to its unique optical properties, but most work has been limited to nanostructures. We report here SPR biosensing with aluminum thin-films using the standard Kretschmann configuration that has previously been dominated by gold films. Electron-beam physical vapor deposition (EBPVD)-prepared Al films oxidize in air to form a nanofilm of Al₂O_3, yielding robust stability for sensing applications in buffered solutions. FDTD simulations revealed a sharp plasmonic dip in the visible range that enables measurement of both angular shift and reflection intensity change at a fixed angle. Bulk and surface tests indicated that Al films exhibited superb sensitivity performance in both categories. Compared to Au, the Al/Al₂O₃ layer showed a marked effect of suppressing nonspecific binding from proteins in human serum. Further characterization indicated that Al film demonstrated a higher sensitivity and a wider working range than Au films when used for SPR imaging analysis. Combined with its economic and manufacturing benefits, the Al thin-film has the potential to become a highly advantageous plasmonic substrate to meet a wide range of biosensing needs in SPR configurations.

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.

Size and morphology dependent surface wetting based on hydrocarbon functionalized nanoparticles

HYPOTHESIS

The wetting properties of films created using metal oxide nanoparticles can be controlled through roughness and chemical functionality; however, other variations such as the size and shape of the particles play an important role in improved understanding of the wetting behaviour of these materials.

EXPERIMENTS

Infrared (IR) spectroscopy and thermogravimetric analysis (TGA) were used to study the chemisorption and grafting density of a carboxylic acid onto the surface of nanoparticles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the morphology and roughness of the nanoparticle films. To investigate the wettability and surface energy of the films, static and dynamic contact angle (CA) measurements were used.

FINDINGS

Smaller, spherical nanoparticles (<50 nm) were observed to create films that displayed greater surface roughness and showed superhydrophobic properties. By comparison, larger, 135 nm spherical nanoparticles showed reduced surface roughness and displayed water contact angles (WCAs) <150°. Since these particles showed similar carboxylate grafting densities, this suggests that there is a particle size limit above which it is not possible to deposit superhydrophobic films. This study also shows that topographical effects brought about by film roughness can be overcome through increasing the carboxylate grafting density on the surface of the nanoparticles. It was observed that films created using mix shape <50 nm nanoparticles with relatively low surface roughness displayed superhydrophobic WCAs and low hysteresis. These particles also possessed a substantially larger carboxylate grafting density, indicating that the extent of functionalization also has a large bearing on the wettability of the films. Herein, we show that particle size, morphology, and reactivity all play important roles in determining the wettability of nanoparticle films.

Streamer Inception from Ultra-Sharp Needles in Mineral Oil Based Nanofluids

Positive and negative streamer inception voltages from ultra-sharp needle tips (with tip radii below 0.5 μm) are measured in TiO2, SiO2, Al2O3, ZnO and C60 nanofluids. The experiments are performed at several concentrations of nanoparticles dispersed in mineral oil. It is found that nanoparticles influence positive and negative streamers in different ways. TiO2, SiO2 and Al2O3 nanoparticles increase the positive streamer inception voltage only, whilst ZnO and C60 nanoparticles augment the streamer inception voltages in both polarities. Using these results, the main hypotheses explaining the improvement in the dielectric strength of the host oil due to the presence of nanoparticles are analyzed. It is found that the water adsorption hypothesis of nanoparticles is consistent with the increments in the reported positive streamer inception voltages. It is also shown that the hypothesis of nanoparticles reducing the electron velocity by hopping transport mechanisms fails to explain the results obtained for negative streamers. Finally, the hypothesis of nanoparticles attaching electrons according to their charging characteristics is found to be consistent with the results hereby presented on negative streamers.

Effect of benzoic acid surface modified alumina nanoparticles on the mechanical properties and crystallization behavior of isotactic polypropylene nanocomposites

The effect of benzoic acid (BA) surface modified alumina (Al₂O₃) nanoparticles (NPs) on the mechanical properties and crystallization behavior of isotactic polypropylene (iPP) nanocomposites was studied. Characterization of the modified Al₂O₃ NPs (BA-Al₂O₃) by FTIR and XRD analyses confirmed that benzoic acid molecules chemisorb on the surface of the NPs, forming benzene groups-rich microstructures. A considerable increase in the tensile strength, flexural modulus, and toughness was observed for the nanocomposites with only 0.2 wt% BA-Al₂O₃. Enhanced interfacial adhesion with the matrix was achieved, which enabled effective reinforcement of the nanocomposites. The higher crystallization temperature along with shorter crystallization halftime indicated the higher nucleation activity of BA-Al₂O₃. Furthermore, the interchain conformational ordering of iPP was significantly accelerated in the presence of the BA-Al₂O₃ NPs. The CH-π interaction between the polymer and BA-Al₂O₃ NPs was considered to facilitate the attachment of the iPP chains and stimulate conformational ordering, crystallization, as well as mechanical properties of nanocomposites.

Environmentally Benign Production of Stretchable and Robust Superhydrophobic Silicone Monoliths

Superhydrophobic materials hold an enormous potential in sectors as important as aerospace, food industries, or biomedicine. Despite this great promise, the lack of environmentally friendly production methods and limited robustness remain the two most pertinent barriers to the scalability, large-area production, and widespread use of superhydrophobic materials. In this work, highly robust superhydrophobic silicone monoliths are produced through a scalable and environmentally friendly emulsion technique. It is first found that stable and surfactantless water-in-polydimethylsiloxane (PDMS) emulsions can be formed through mechanical mixing. Increasing the internal phase fraction of the precursor emulsion is found to increase porosity and microtexture of the final monoliths, rendering them superhydrophobic. Silica nanoparticles can also be dispersed in the aqueous internal phase to create micro/nanotextured monoliths, giving further improvements in superhydrophobicity. Due to the elastomeric nature of PDMS, superhydrophobicity can be maintained even while the material is mechanically strained or compressed. In addition, because of their self-similarity, the monoliths show outstanding robustness to knife-scratch, tape-peel, and finger-wipe tests, as well as rigorous sandpaper abrasion. Superhydrophobicity was also unchanged when exposed to adverse environmental conditions including corrosive solutions, UV light, extreme temperatures, and high-energy droplet impact. Finally, important properties for eventual adoption in real-world applications including self-cleaning, stain-repellence, and blood-repellence are demonstrated.

Dually Prewetted Underwater Superoleophobic and under Oil Superhydrophobic Fabric for Successive Separation of Light Oil/Water/Heavy Oil Three-Phase Mixtures

Remediation of oil spills requires new technologies to separate light oil/water/heavy oil mixtures. Low-cost, biological, and environmentally friendly materials are needed to treat water pollution caused by oils. In this study, a corn straw powder (CSP)-coated fabric (CSPF) was fabricated by spraying waste CSP and polyurethane onto amphiphilic cotton fabric, and thus, the wettability of CSPF is enhanced by taking advantage of the hierarchical structure and increased surface roughness. Therefore, the CSPF could be dually prewetted (DCSPF) with both water and oil, and it showed underwater superoleophobic and under oil superhydrophobic properties without any further chemical modification. When applied to light oil/water/heavy oil separation, the DCSPF could be used to successively separate light oil/water/heavy oil three-phase mixtures under gravity with a high separation efficiency and flux. In addition, the DCSPF showed excellent structural and chemical stability according to repeated cycling and corrosive solution/oil separation experiments. The results of this study are of value in providing a simple, low-cost, and environment-friendly approach for application in the field of successive separation of light oil/water/heavy oil three-phase mixtures.