Search results

The purpose of this paper is to evaluate the effect of micro-nano mixed super-hydrophobic structure on corrosion resistance and mechanism of magnesium alloys.

A super-hydrophobic surface was fabricated on AZ91 and WE43 magnesium alloys by laser etching and micro-arc oxidation (MAO) with SiO₂ nanoparticles coating and low surface energy material modification. The corrosion resistance properties of the prepared super-hydrophobic surfaces were studied based on polarization curves and immersion tests.

Compared with bare substrates, the corrosion resistance of super-hydrophobic surfaces was improved significantly. The corrosion resistance of super-hydrophobic surface is related to micro-nano composite structure, static contact angle and pretreatment method. The more uniform the microstructure and the larger the static contact angle, the better the corrosion resistance of the super-hydrophobic surface. The corrosion resistance of super-hydrophobic by MAO is better than that of laser machining. Corrosion of super-hydrophobic surface can be divided into air valley action, physical shielding, pretreatment layer action and substrate corrosion.

The super-hydrophobic coatings can reduce the contact of matrix with water so that a super-hydrophobic coating would be an effective way for magnesium alloy anti-corrosion. Therefore, the corrosion resistance properties and mechanism of the prepared super-hydrophobic magnesium alloys were investigated in detail.

Usual lab coats are designed to protect the wearer from the splats of chemicals, oil, dirt, etc. Simple lab coats are damaged by concentrated acids, thus quickly showing typical small holes along the front when worn in a laboratory where acids are used. For intense handling of acids and other chemicals, special protective lab coats with rubber or vinyl apron or chemical-resistant overalls are used. The purpose of this paper is to investigate the possibility to protect lab coats from acid damages by finishing them with commercially available hydrophobization chemicals.

Two commercial hydrophobic sprays were applied on cotton, polyamide and polyester lab coat materials. Contact and roll-off angles were compared with the untreated textile fabrics before typical laboratory acids were applied on the fabrics. Finally, antibacterial properties of the finished textiles were examined.

Spray 1 resulted in significantly increased hydrophobicity, while spray 2 did not have any influence on the results. With spray 1, the originally hydrophobic fabrics became more hydrophobic, and even the originally strongly hydrophilic fabrics showed large contact angles of 130–140°. Roll-off angles were significantly reduced from 40 to 50° (for the hydrophobic fabrics) or even 90° (in case of hydrophilic fabrics) to approximately 15–25°. Correspondingly, spray 1 showed an increase of the acid resistance of the finished textile fabrics of up to 30 min for the originally hydrophobic fabrics and up to 20 min for the originally hydrophilic ones, with only one polyester fabric showing no acid resistance at all, while spray 2 led to increased antibacterial properties.

While spray 1 can support laboratory safety by increasing the time until acids penetrate through a lab coat, spray 2 can support sterile work in a biological laboratory.

To the best of the authors’ knowledge, increasing the acid resistance as well as the antibacterial properties of lab coats with easily accessible sprays has not been reported before in the scientific literature.

This paper focuses on the fluid-structure interaction (FSI) analysis of moisture induced stress for the flip chip ball grid array (FCBGA) package with hydrophobic and hydrophilic materials during the reflow soldering process. The purpose of this paper is to analyze the influence of moisture concentration and FCBGA with hydrophobic material on induced pressure and stress in the package at varies times.

The present study analyzed the warpage deformation during the reflow process via visual inspection machine (complied to Joint Electron Device Engineering Council standard) and FSI simulation by using ANSYS/FLUENT package. The direct concentration approach is used to model moisture diffusion and ANSYS is used to predict the Von-Misses stress. Models of Test Vehicle 1 (similar to Xie et al., 2009b) and Test Vehicle 2 (FCBGA package) with the combination of hydrophobic and hydrophilic materials are performed. The simulation for different moisture concentrations with reflows process time has been conducted.

The results from the mechanical reliability study indicate that the FSI analysis is found to be in good agreement with the published study and acceptable agreement with the experimental result. The maximum Von-Misses stress induced by the moisture significantly increased on FCBGA with hydrophobic material compared to FCBGA with a hydrophilic material. The presence of hydrophobic material that hinders the moisture desorption process. The analysis also illustrated the moisture could very possibly reside in electronic packaging and developed beyond saturated vapor into superheated vapor or compressed liquid, which exposed electronic packaging to higher stresses.

The findings provide valuable guidelines and references to engineers and packaging designers during the reflow soldering process in the microelectronics industry.

Studies on the influence of moisture concentration and hydrophobic material are still limited and studies on FCBGA package warpage under reflow process involving the effect of hydrophobic and hydrophilic materials are rarely reported. Thus, this study is important to effectively bridge the research gap and yield appropriate guidelines in the microelectronics industry.

Internal hydrophobation by adding hydrophobic agents during the mixing process is a method for reducing water permeability of cement based materials. It can be used as an alternative to other methods such as reducing water cement ratio (w/c) or using silica fume (SF). However, it may affect other properties of cement based materials such as compressive strength. In this paper the results of an experimental study on compressive strength of different hcps with main variables w/c, SF and hydrophobic agents are presented. Rapeseed oil and alkyl alkoxysilane were selected as hydrophobic agents. Although, a low dosage of hydrophobic agents can be more effective than lowering w/c or adding SF in reducing water permeability, an obvious reduction was observed in compressive strength by this way of internal hydrophobation compared to the other above mentioned methods. Different reasons such as lower hydration degree, chemical reactions of hydrophobic agents and non-uniform distribution of hydrophobic materials in the hcp could have resulted in lower compressive strength of hydrophobed samples. Using other types of hydrophobic agents or impregnation after the curing process can be other alternatives which would have less effect on compressive strength.

The purpose of this study is to analyze the heat transfer and flow enhancement of an Al₂O₃-water nanofluid filling an inclined channel whose lower wall is embedded with periodically placed discrete hydrophobic heat sources. Formation of a thin depletion layer of low viscosity over each hydrophobic heated patch leads to the velocity slip and temperature jump condition at the interface of the hydrophobic patch.

The mixed convection of the nanofluid is analysed based on the two-phase non-homogeneous model. The governing equations are solved numerically through a control volume approach. A periodic boundary condition is adopted along the longitudinal direction of the modulated channel. A velocity slip and temperature jump condition are imposed along with the hydrophobic heated stripes. The paper has validated the present non-homogeneous model with existing experimental and numerical results for particular cases. The impact of temperature jump condition and slip velocity on the flow and thermal field of the nanofluid in mixed convection is analysed for a wide range of governing parameters, namely, Reynolds number (50 ≤ Re ≤ 150), Grashof number ( 103≤Gr≤5×104), nanoparticle bulk volume fraction ( 0.01≤φb≤0.05), nanoparticle diameter ( 30≤dp≤60) and the angle of inclination ( −60°≤σ≤60°).

The presence of the thin depletion layer above the heated stripes reduces the heat transfer and augments the volume flow rate. Consideration of the nanofluid as a coolant enhances the rate of heat transfer, as well as the entropy generation and friction factor compared to the clear fluid. However, the rate of increment in heat transfer suppresses by a significant margin of the loss due to enhanced entropy generation and friction factor. Heat transfer performance of the channel diminishes as the channel inclination angle with the horizontal is increased. The paper has also compared the non-homogeneous model with the corresponding homogeneous model. In the non-homogeneous formulation, the nanoparticle distribution is directly affected by the slip conditions by virtue of the no-normal flux of nanoparticles on the slip planes. For this, the slip stripes augment the impact of nanoparticle volume fraction compared to the no-slip case.

This paper finds that the periodically arranged hydrophobic heat sources on the lower wall of the channel create a significant augmentation in the volume flow rate, which may be crucial to augment the transport process in mini- or micro-channels. This type of configuration has not been addressed in the existing literature.

The maintenance of the air–water interface is crucial for the drag reduction on hydrophobic surfaces. But the air bubbles become unstable and even washed away under high speed flow, causing the failure of surface hydrophobicity. Thereby, this paper aims to understand the relations between bubble behaviors and surface properties, flow conditions and to discover new methods to maintain the air–water interface.

Bubble properties on hydrophobic surfaces were characterized using single-component multiphase lattice Boltzmann simulation. Three equations of state (EOSs), including the Peng–Robinson, Carnahan–Starling and modified Kaplun–Meshalkin EOSs, were incorporated to achieve high density ratios.

Both the static and dynamic properties of bubbles on hydrophobic surfaces were investigated and analyzed under different flow conditions, solid–liquid interactions and surface topology.

By revealing the properties of bubbles on hydrophobic surfaces, the effects of flow conditions and surface properties were characterized. The maintenance method of air–water interface can be proposed according to the bubble properties in the study.

The paper aims to improve the protective and comfort properties of both woven and knitted acrylic fabrics by applying a hybrid waterborne polyurethane/fluorocarbon hydrophobic finish.

In this study, it was found that the transportation of water from fabrics is one of the important textile parameters. To improve this property, a polyurethane-based finish (Dicrylan BSRN^®) and an oil- and water-repellent finish (Oleophobol ZSR^®) were applied by using the pad-dry-cure method. After applying the finishes, the resultant fabric samples were investigated for various textile properties.

The application of Oleophobol ZSR^® increased the absorbency time, indicating that the fabric became hydrophobic, whereas the application of Dicrylan BSRN^® finish improved the moisture management properties of the woven acrylic. The tensile strength of the woven acrylic fabric was not significantly affected by the application of these finishes. The contact angle of treated knitted fabrics increased and air permeability decreased with an increase in the concentration of Oleophobol ZSR^®.

Moisture management is one of the crucial performance criteria in today’s apparel industry. Therefore, fluorochemicals are one of the major precursors used in water-repellent finishes and waterproof membranes in outdoor garments. Based on this fact, this research work focused on the textile sector, where moisture management is required.

This is the first report about the combined application of waterborne polyurethane and fluorochemical-based finishes on acrylic fabrics to tune their comfort and hydrophobic properties.

This study aims to prepare UV protection and hydrophobic fabric through modifying cotton fabric by graphene oxide and silane coupling agent. The graphene oxide and silane coupling agent (KH570) are anchored on the cotton fabric by a stable chemical bond.

Graphene oxide was prepared by modified Hummers method. The fabric sample was treated with graphene oxide and silane coupling agent KH570 using simple dipping-padding-drying method. The effects of the dosage of graphene oxide, silane coupling agent KH570 and curing temperature were determined by single variable experiment and orthogonal experiment, The UVA and UVB transmittances in ultraviolet light of the sample fabric were characterized, and the contact angle test method with water was used to indicate the hydrophobicity of the sample fabric. The structure and surface of the fabric were analyzed using Fourier-transform infrared spectroscopy and scanning electron microscopy.

The cotton fabric was successfully modified by graphene oxide and silane coupling agent KH570. Compared with the untreated fabric, the surface of the fabric was smooth, and there was no gap on the fiber. The graphene oxide, silane coupling agent KH570 and cotton fabric combined tightly. The UPF value of the modified fabric was 50+, and the contact angle reached 138.1°. It had excellent UV protection and hydrophobic properties.

Although graphene oxide and silane coupling agents KH570 had successfully endowed the cotton fabric with good UV protection and hydrophobic properties, graphene oxide and silane coupling agent KH570 are expensive and used in large quantities. There are certain limitations in the actual life and production process.

After treating with silane coupling agent, the hydrophilic fabric treated with graphene oxide is being translated into hydrophobic, and graphene oxide bonded with cotton. The modified fabrics also have excellent UV protection. This fabric can be used for outdoor sports such as clothes and tents.

Cotton fabric treated with graphene oxide generally by simple dip-dry-cure method is hydrophilic and graphene oxide is easy to drop. The usage of silane coupling agent KH570 as a crosslinking agent to link graphene oxide and cotton fibers has not been reported yet. The modified fabrics have both UV protection and hydrophobic properties.

This paper introduced the simple synthesis process of self-cleaning coating with fog-resistance property using hydrophobic polydimethylsiloxane (PDMS) polymer and nano-calcium carbonate (nano-CaCO₃) and titanium dioxide (TiO₂).

The synthesis method of PDMS/nano-CaCO₃-TiO₂ is based on sol-gel process. The crosslinking between PDMS and nanoparticles is driven by the covalent bond at temperature of 50°C. The 3-Aminopropyltriethoxysilane is used as binder for nanoparticles attachment in polymer matrix. Two fabrication methods are used, which are dip- and spray-coating methods.

The prepared coated glass fulfilled the requirement of standard self-cleaning and fog-resistance performance. For the self-cleaning test BS EN 1096-5:2016, the coated glasses exhibited the dust haze value around 20%–25% at tilt angle of 10°. For the antifog test, the coated glasses showed the fog haze value were below 2% and the gloss value were above 85%. The obtained results completely achieved the standard antifog value ASTM F659-06 protocol.

Findings will provide an infrastructure support for the building glass to enhance building’s energy efficiency, cleaning performance and friendly environment.

This study proposed the simple synthesis method using hydrophobic polymer and nano-CaCO₃ and nano-TiO₂, which can achieve optimum self-cleaning property at low tilt angle and fog-resistance performance for building glass.

The research findings have high potential for building company, cleaning building company and government sector. The proposed project capable to reduces the energy consumption about 20% per annum due to labor cost, time-consuming and safety during manual cleaning.

The novel method to develop self-cleaning coating with fog-resistance using simple synthesis process and fabrication method for building glass application.

This study aims to fabricate the acrylic-based polymeric composite coating with a hydrophobic surface associated with natural oil polyol (NOP) and polydimethylsiloxane with the incorporation of 3 Wt.% SiO₂ nanoparticle (SiO₂np) against the corrosive NaCl media.

The structural properties of the formulated polymeric composite coatings were investigated by using Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, water contact angle (WCA) and cross-hatch (X-Hatch) tests. The WCA measurement was used to study the surface wettability of the formulated polymeric composite coatings. The corrosion protection performance of the nanocomposite coated on the mild steel substrate was studied by immersing the samples in 3.5 Wt.% NaCl solution for 30 days using electrochemical impedance spectroscopy.

The enhanced polymeric composite coating system performed with an excellent increase in the WCA up to 111.1° which is good hydrophobic nature and very high coating resistance in the range of 10¹⁰ Ω attributed to the superiority of SiO₂np.

The incorporation of SiO₂np into the polymeric coating could enhance the surface roughness and hydrophobic properties that could increase corrosion protection. This approach is a novel attempt of using NOP along with the addition of SiO₂np.