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

HypothesisThe 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.ExperimentsThe 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.FindingsCombining the Al2O3 nanoparticles with epoxy resin was observed to create highly hydrophobic coatings that displayed water contact angles (WCAs) between 145-150°. 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 75-125° 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

HypothesisThe 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.ExperimentsInfrared (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.FindingsSmaller, 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

Carboxylation and Decarboxylation of Aluminum Oxide Nanoparticles Using Bifunctional Carboxylic Acids and Octylamine

The carboxylation of alumina nanoparticles (NPs), with bifunctional carboxylic acids, provides molecular anchors that are used for building more complexed structures via either physisorption or chemisorption. Colloidal suspensions of the NPs may be prepared by covalently bonding a series of carboxylic acids with secondary functional groups (HO2C-R-X) to the surface of the NPs: lysine (X = NH2), p-hydroxybenzoic acid (X = OH), fumaric acid (X = CO2H), and 4-formylbenzoic acid (X = C(O)H). Subsequent reaction with octylamine at either 25°C or 70°C was investigated. Fourier transform IR-attenuated reflectance spectroscopy (FTIR-ATR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) along with energy dispersive X-ray (EDX) analysis were used to characterize the bifunctionalized monolayers and/or multilayer corona surrounding the alumina NPs and investigate the reaction mechanism of octylamine with the functional groups (X) of the NPs. Except for the fumaric functionalized NPs, addition of octylamine to the functionalized NPs leads to removal of excess carboxylic acid corona from the surface via an amide formation. The extent of the multilayer is dependent on the strength of the acid⋯acid interaction

Controlling the wettability of plastic by thermally embedding coated aluminium oxide nanoparticles into the surface

HypothesisNanoparticle embedding into the surface of plastics provides an effective anchor that improves the durability of coatings formed from functionalized nanoparticles. Coatings formed from thermally embedded particles show superior wear resistance relative to coatings formed from non-embedded particles. As a consequence of this, embedded nanoparticles functionalized with hydrophilic and hydrophobic carboxylates are better suited for controlling the wettability of plastics than when the nanoparticles are deposited onto the plastic under ambient conditions.ExperimentsCarboxylate-functionalized Al2O3 nanoparticles were embedded into ethylene vinyl acetate through spray coating the particles onto the substrate during heating. Sonication was used to remove excess particles that did not become embedded into the material. Coatings formed from the embedded particles were characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The wettability of the coatings was characterized using static and dynamic contact angle (CA) measurements to measure the apparent water contact angles, and sliding angle measurements, whilst the durability of the coatings was studied using scratch testing, tape peel tests, and abrasion tests. The build-up of fog on the substrates was also studied through exposing the surfaces to water vapour.FindingsThermal embedding of the particles into the surface of the plastic was observed to occur when the material was heated to temperatures around its melting temperature. AFM and SEM showed that plastic embedded with the nanoparticles possessed a morphology that was substantially rougher than the untreated plastic. CA measurements showed that plastic embedded with hydrophobic isostearate functionalized nanoparticles was highly hydrophobic and displayed a CA of approximately 152°. Dynamic CA measurements and sliding angle measurements revealed that plastic embedded with the isostearate functionalized nanoparticles showed petal-like wetting behavior. Furthermore, it was observed that the CA of the plastic could be varied from highly hydrophobic to highly hydrophilic through embedding varying amounts of isostearate and hydrophilic 2-[2-(2-methoxyethoxy)ethoxy]acetate functionalized Al2O3 nanoparticles into the surface of the material. Scratch testing showed that thermally embedding the nanoparticles into the plastic substantially improved their abrasion resistance, relative to when the nanoparticles are deposited onto the non-heated material. This methodology indicates that embedding nanoparticles into plastics creates durable coatings that can display variable wettability. Consequently, this methodology could be useful in applications where it is desirable to keep plastics dry, such as for food packaging or medical devices

“How do hospitality leaders and employees perceive and experience cultural diversity in social interactions in the workplace?”

The purpose of this study was to explore how cultural diversity in social interactions between co-workers in the hospitality industry. The research question is “How do hospitality leaders and employees perceive and experience cultural diversity in social interactions in the workplace?”. To answer this research question, a qualitative, exploratory research design was used to collect narratives. This through semi-structured interviews. The interview questions focused on topics related to cultural diversity and social interactions, such as perceptions of cultural diversity, and experiences with cultural diversity. The interviews were transcribed, and analyzed following the format of a thematic analysis

Simultaneous diagonalisation of the covariance and complementary covariance matrices in quaternion widely linear signal processing

Recent developments in quaternion-valued widely linear processing have established that the exploitation of complete second-order statistics requires consideration of both the standard covariance and the three complementary covariance matrices. Although such matrices have a tremendous amount of structure and their decomposition is a powerful tool in a variety of applications, the non-commutative nature of the quaternion product has been prohibitive to the development of quaternion uncorrelating transforms. To this end, we introduce novel techniques for a simultaneous decomposition of the covariance and complementary covariance matrices in the quaternion domain, whereby the quaternion version of the Takagi factorisation is explored to diagonalise symmetric quaternion-valued matrices. This gives new insights into the quaternion uncorrelating transform (QUT) and forms a basis for the proposed quaternion approximate uncorrelating transform (QAUT) which simultaneously diagonalises all four covariance matrices associated with improper quaternion signals. The effectiveness of the proposed uncorrelating transforms is validated by simulations on both synthetic and real-world quaternion-valued signals.Comment: 41 pages, single column, 10 figure

New insights into the interactions between asphaltene and a low surface energy anionic surfactant under low and high brine salinity

Hypothesis: The hyperbranched chains on the tail of low surface energy surfactants (LSES) causes lowering of surface free energy and rock wettability alteration, offering significant improvement in oil recovery in asphaltene oil reservoirs.Experiments: Oil sweep efficiency was determined by fluid displacement in pure brine and LSES-brine solutions in a microfluidic pattern that was representative of a sandstone cross-section. Interfacial tension (IFT), wettability alteration, and Raman and X-ray photoelectron spectroscopy (XPS) were used to measure the changes of asphaltene interactions with oil-aged substrate after surface treating with brine and surfactant-brine solutions.Findings: The hyperbranched LSES yielded a significant increase in the original-oil-in-place (OOIP) recovery (58%) relative to brine flooding (25%), even in the presence of asphaltene. Raman spectra showed the LSES-brine solutions to be capable of causing change to the asphaltene aggregate size after centrifugation treatment

Silica Nanoparticle Enhancement in the Efficiency of Surfactant Flooding of Heavy Oil in a Glass Micromodel

The synergic effects of fumed-Si nanoparticles (Si-NPs) in combination with sodium dodecyl sulfate (SDS) surfactant as suitable agents for oil displacing in enhanced oil recovery (EOR) are evaluated using a 5-spot glass micromodel. Optimum oil recovery (45%) is obtained for SDS near the critical micelle concentration; however, the addition of fumed silica nanoparticles (Si-NPs) enables a further 13% enhancement in oil recovery for the maximum concentration of the SDS/Si-NPs (2.2 wt.%), as well as delaying the breakthrough point. The optimum mass ratio of SDS:Si-NP (1:11) suggests that the Si-NPs are aggregated by the SDS micelles; consistent with increased viscosity upon addition of Si-NPs. The presence of the Si-NPs also greatly increases the wettability on the glass surface, with a decrease in the contact angle from 73° for SDS (1800 ppm) to 11° for SDS/Si-NPs (1800 ppm/2.0 wt.%). The effective changes in the oil sweeping mechanism are directly observed in glass micromodel and correlate to these physical measurements. The results demonstrated the addition of Si-NPs to SDS solutions made a significant improvement to oil recovery values and potentially beneficial in EOR applications

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

The formation of materials with tunable wettability is important for applications ranging from antifouling to waterproofing surfaces. We report the use of various low-cost and nonhazardous hydrocarbon materials to tune the surface properties of aluminum oxide nanoparticles (NPs) from superhydrophilic to superhydrophobic through covalent functionalization. The hydrocarbon surfaces are compared with a fluorinated surface for wettability and surface energy properties. The role of NPs’ hydrophobicity on their dynamic interfacial behavior at the oil–water interface and their ability to form stable emulsions is also explored. The spray-coated NPs provide textured surfaces (regardless of functionality), with water contact angles (θ) of 10–150° based on their surface functionality. The superhydrophobic NPs are able to reduce the interfacial tension of various oil–water interfaces by behaving as surfactants