Recent Advances in Superhydrophobic Electrodeposits

Investigation of Automotive LiDAR Vision in Rain from Material and Optical Perspectives

With the emergence of autonomous functions in road vehicles, there has been increased use of Advanced Driver Assistance Systems comprising various sensors to perform automated tasks. Light Detection and Ranging (LiDAR) is one of the most important types of optical sensor, detecting the positions of obstacles by representing them as clusters of points in three-dimensional space. LiDAR performance degrades significantly when a vehicle is driving in the rain as raindrops adhere to the outer surface of the sensor assembly. Performance degradation behaviors include missing points and reduced reflectivity of the points. It was found that the extent of degradation is highly dependent on the interface material properties. This subsequently affects the shapes of the adherent droplets, causing different perturbations to the optical rays. A fundamental investigation is performed on the protective polycarbonate cover of a LiDAR assembly coated with four classes of material-hydrophilic, almost-hydrophobic, hydrophobic, and superhydrophobic. Water droplets are controllably dispensed onto the cover to quantify the signal alteration due to the different droplets of various sizes and shapes. To further understand the effects of droplet motion on LiDAR signals, sliding droplet conditions are simulated using numerical analysis. The results are validated with physical optical tests, using a 905 nm laser source and receiver to mimic the LiDAR detection mechanism. Comprehensive explanations of LiDAR performance degradation in rain are presented from both material and optical perspectives. These can aid component selection and the development of signal-enhancing strategies for the integration of LiDARs into vehicle designs to minimize the impact of rain.

Laser-Assisted Nanotexturing and Silver Immobilization on Titanium Implant Surfaces to Enhance Bone Cell Mineralization and Antimicrobial Properties

Despite the great advancement and wide use of titanium (Ti) and Ti-based alloys in different orthopedic implants, device-related infections remain the major complication in modern orthopedic and trauma surgery. Most of these infections are often caused by both poor antibacterial and osteoinductive properties of the implant surface. Here, we have demonstrated a facile two-step laser nanotexturing and immobilization of silver onto the titanium implants to improve both cellular integration and antibacterial properties of Ti surfaces. The required threshold laser processing power for effective nanotexturing and osseointegration was systematically determined by the level of osteoblast cells mineralized on the laser nanotextured Ti (LN-Ti) surfaces using a neodymium-doped yttrium aluminum garnet laser (Nd:YAG, wavelength of 1.06 μm). Laser processing powers above 24 W resulted in the formation of hierarchical nanoporous structures (average pore 190 nm) on the Ti surface with a 2.5-fold increase in osseointegration as compared to the pristine Ti surface. Immobilization of silver nanoparticles onto the LN-Ti surface was conducted by dip coating in an aqueous silver ionic solution and subsequently converted to silver nanoparticles (AgNPs) by using a low power laser-assisted photocatalytic reduction process. Structural and surface morphology analysis via XRD and SEM revealed a uniform distribution of Ag and the formation of an AgTi-alloy interface on the Ti surface. The antibacterial efficacy of the LN-Ti with laser immobilized silver (LN-Ti/LI-Ag) was tested against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The LN-Ti/LI-Ag surface was observed to have efficient and stable antimicrobial properties for over 6 days. In addition, it was found that the LN-Ti/LI-Ag maintained a cytocompatibility and bone cell mineralization property similar to the LN-Ti surface. The differential toxicity of the LN-Ti/LI-Ag between bacterial and cellular species qualifies this approach as a promising candidate for novel rapid surface modification of biomedical metal implants.

Lotus-Leaf-Inspired Biomimetic Coatings: Different Types, Key Properties, and Applications in Infrastructures

A universal infrastructural issue is wetting of surfaces; millions of dollars are invested annually for rehabilitation and maintenance of infrastructures including roadways and buildings to fix the damages caused by moisture and frost. The biomimicry of the lotus leaf can provide superhydrophobic surfaces that can repel water droplets, thus reducing the penetration of moisture, which is linked with many deterioration mechanisms in infrastructures, such as steel corrosion, sulfate attack, alkali-aggregate reactions, and freezing and thawing. In cold-region countries, the extent of frost damage due to freezing of moisture in many components of infrastructures will be decreased significantly if water penetration can be minimized. Consequently, it will greatly reduce the maintenance and rehabilitation costs of infrastructures. The present study was conducted to explore any attempted biomimicry of the lotus leaf to produce biomimetic coatings. It focuses on anti-wetting characteristics (e.g., superhydrophobicity, sliding angle, contact angle), self-cleaning capability, durability, and some special properties (e.g., light absorbance and transmission, anti-icing capacity, anti-fouling ability) of lotus-leaf-inspired biomimetic coatings. This study also highlights the potential applications of such coatings, particularly in infrastructures. The most abundant research across coating materials showed superhydrophobicity as being well-tested while self-cleaning capacity and durability remain among the properties that require further research with existing promise. In addition, the special properties of many coating materials should be validated before practical applications.

Long-Term Durability of Robust Super-Hydrophobic Co–Ni-Based Coatings Produced by Electrochemical Deposition

The long-term durability for two kinds of Co–Ni-based robust coatings, the Co–Ni super-hydrophobic (Co–Ni SHPB) coating and Co–Ni/WC super-hydrophobic (Co–Ni/WC SHPB) coating, was analyzed through an immersion test in 3.5 wt.% NaCl solution. The evolution of their surface properties was characterized by scanning electron microscope (SEM) images, energy-dispersive spectrometry (EDS), a wettability measurement and X-ray photoelectron spectrometer (XPS), and the evolution of anti-corrosion mechanisms was evaluated with electrochemical measurements. The results show that as-prepared two kinds of robust coatings display a good long-term durability, with the Co–Ni SHPB coating and Co–Ni/WC SHPB coating losing their super-hydrophobicity after being immersed for more than 10 days. Additionally, both kinds of coatings present efficient corrosion protection even after long-term immersion.

One-step fabrication of soft calcium superhydrophobic surfaces by a simple electrodeposition process

A simple, one-step electrodeposition process was rapidly performed on a metal substrate to fabricate calcium superhydrophobic surfaces in an electrolyte containing calcium chloride (CaCl₂), myristic acid (CH₃(CH₂)₁₂COOH), and ethanol, which can avoid the intricate post-processing of surface treatment. The morphology and surface chemical compositions of the fabricated superhydrophobic surfaces were systematically examined by means of SEM, XRD, and FTIR, respectively. The results indicate that the deposited surfaces were mainly composed of calcium myristate, which can dramatically lower surface free energy. The shortest process for constructing a superhydrophobic surface is about 0.5 min, and the maximum contact angle of the as-prepared surfaces can reach as high as 166°, showing excellent superhydrophobicity. By adjusting the electrodeposition time, the structure of the cathodic surface transforms from the turfgrass structure, loose flower structures, larger and dense flower structures, secondary flower structures, and then into tertiary or more flower structures. The superhydrophobic surfaces showed excellent rebound performance with a high-speed camera. After a pressing force, their hardness increases, but the superhydrophobic performance is not weakened. Inversely, the bouncing performance is enhanced. This electrodeposition process offers a promising approach for large areas of superhydrophobic surfaces on conductive metals and strongly impacts the dynamics of water droplets.

We investigated a one-step method for calcium superhydrophobic surface preparation and researched the formation process of loose, flower-like microstructures. Also, we found that the pressing force strongly impacts the dynamics of water droplets.

Sub-nanometer scale investigation of in situ wettability using environmental transmission electron microscopy

HYPOTHESIS

Contact angle measurements alongside Young's equation have been frequently used to quantitatively characterize the wettabilities of solid surfaces. In the literature, the Wenzel and Cassie-Baxter models have been proposed to account for surface roughness and chemical heterogeneity, while precursor film models have been developed to account for stress singularity. However, the majority of these models were derived based on theoretical analysis or indirect experimental measurements. We hypothesize that sub-nanometer-scale in situ investigations will elucidate additional complexities that impact wettability characterization.

EXPERIMENTS

To develop further insights into in situ wettability, we provide the first direct experimental observation of fluid-solid occupancies at three-phase contacts at sub-nanometer resolution, using environmental transmission electron microscopy.

FINDINGS

Considering the partially spreading phenomenon and capillarity, we provide an improved physics-based interpretation of measuring the sub-nanometer-scale contact angle at the inflection point of the fluid-fluid interface. The difference between this angle and the commonly-used apparent one measured at a lower resolution is also discussed. Furthermore, we provide direct experimental evidence for the density differences between the adsorbed wetting film and the bulk wetting phase. For the effect of surface roughness, the applicability of the Wenzel model is discussed based on the observed in situ solid-fluid occupancies.

Electrophoretic-deposited Superhydrophobic Coatings

Electrophoretic deposition (EPD) is an excellent surface coating approach widely investigated for applications ranging from solar cells, batteries, electrochemical capacitors, solid oxide fuel cells, sensors, molecular sieves, corrosion-resistant coatings, and biomedical materials. On the other hand, superhydrophobic (SHPC) surfaces have enticed substantial recent research interest owing to their superb surface properties. Here, we provide a comprehensive review of electrophoretic-deposited SHPC coatings. Concise descriptions of EPD and superhydrophobicity are provided first, followed by a brief mentioning of works reported on electrophoretic-deposited SHPC coatings by one-step or two-step processing (§2.1). The next section (§2.2) delivers a comprehensive description of these reports based on the micro/nanoparticles used. Works reported in specific applications such as anti-corrosion, biomedical, and oil-separation are described in §2.3. Future scopes of research also presented.

Electroplated Functional Materials with 3D Nanostructures Defined by Advanced Optical Lithography and Their Emerging Applications

Electroplating has been favored to date as a surface treatment technology in various industries in the development of semiconductors, automobiles, ships, and steel due to its advantages of being a simple, solution-based process, with low cost and high throughput. Recently, classical electroplating has been reborn as an advanced manufacturing process for functional materials by combining it with unconventional optical three-dimensional (3D) nanofabrication techniques capable of generating polymer templates with high-resolution 3D periodic nanostructures. The bottom-up filling behavior of electroplating rising from a seed layer makes it possible to densely fill the nanoporous network of the template with heterogeneous inorganic materials. At this time, understanding and optimizing the process parameters (e.g., additive, current density, type of current waveform, etc.) of electroplating is critical for defect control. In addition, since electroplating is generally performed near room temperature, unlike other thin film deposition techniques, structural damage to the polymer template by heat during electroplating is almost negligible. Based on the excellent compatibility of electroplating and optical 3D nanofabrication, innovative functional materials with 3D periodic nanostructures targeting electrochemical or energy-related applications have been created. In this mini review, a strategy for producing functional materials with 3D periodic nanostructures through a templating process will be covered, and the recent cases of successful applications to electrodes for energy storage devices, electrocatalysts, and thermoelectric materials will be summarized. We will also discuss technical issues that need to be considered in the process to improve the quality of the resulting functional materials with 3D nanoarchitectures.

Scaling of roughness and porosity in thin film deposition with mixed transport mechanisms and adsorption barriers

Thin film deposition with particle transport mixing collimated and diffusive components and with barriers for adsorption are studied using numerical simulations and scaling approaches. Biased random walks on lattices are used to model the particle flux and the analogy with advective-diffusive transport is used to define a Peclet number P that represents the effect of the bias towards the substrate. An aggregation probability that relates the rates of adsorption and of the dominant transport mechanism plays the role of a Damkohler number D, where D≲1 is set to describe moderate to low adsorption rates. Very porous deposits with sparse branches are obtained with P≪1, whereas low porosity deposits with large height fluctuations at short scales are obtained with P≫1. For P≳1 in which the field bias is intense, an initial random deposition is followed by Kardar-Parisi-Zhang (KPZ) roughening. As the transport is displaced from those limiting conditions, the interplay of the transport and adsorption mechanisms establishes a condition to produce films with the smoothest surfaces for a constant deposited mass: with low adsorption barriers, a balance of random and collimated flux is required, whereas for high barriers the smoothest surfaces are obtained with P∼D^{1/2}. For intense bias, the roughness is shown to be a power law of P/D, whose exponent depends on the growth exponent β of the KPZ class, and the porosity has a superuniversal scaling as (P/D)^{-1/3}. We also study a generalized ballistic deposition model with slippery particle aggregation that shows the universality of these relations in growth with dominant collimated flux, particle adsorption at any point of the deposit, and negligible adsorbate diffusion, in contrast with the models where aggregation is restricted to the outer surface.

Superhydrophobic, Elastic, and Conducting Polyurethane-Carbon Nanotube-Silane-Aerogel Composite Microfiber

Flexible fibers composed of a conductive material mixed with a polymer matrix are useful in wearable electronic devices. However, the presence of the conductive material often reduces the flexibility of the fiber, while the conductivity may be affected by environmental factors such as water and moisture. To address these issues, we developed a new conductive fiber by mixing carbon nanotubes (CNT) with a polyurethane (PU) matrix. A silane ((heptadecafluoro-1,1,2,2-tetra-hydrodecyl)trichlorosilane) was added to improve the strain value of the fiber from 155% to 228%. Moreover, silica aerogel particles were embedded on the fiber surface to increase the water contact angle (WCA) and minimize the effect of water on the conductivity of the fiber. As a result, the fabricated PU-CNT-silane-aerogel composite microfiber maintained a WCA of ~140° even after heating at 250 °C for 30 min. We expect this method of incorporating silane and aerogel to help the development of conductive fibers with high flexibility that are capable of stable operation in wet or humid environments.

Study of Infrared Laser Parameters on Surface Morphology and Hydrophobic Properties

Many studies have shown that super hydrophobic surfaces have been applied to micro–nano structures and low surface energy materials. In the present study, infrared laser scanning and simple salinization modification were used to improve the hydrophobicity of a surface. When the scanning speed was 100 mm/s, the laser power was 30 W and the scanning interval was 200 μm, the apparent contact angle of surface was up to 157°. The assessment of surface characteristics revealed that decreasing scanning speed or increasing laser power were able to improve the hydrophobicity of the surface. After aging treatment, the superhydrophobic surface prepared by this method still had good durability.

Robust Super-Hydrophobic Coating Prepared by Electrochemical Surface Engineering for Corrosion Protection

Corrosion—reactions occuring between engineering materials and their environment—can cause material failure and catastrophic accidents, which have a serious impact on economic development and social stability. Recently, super-hydrophobic coatings have received much attention due to their effectiveness in preventing engineering materials from further corrosion. In this paper, basic principles of wetting properties and corrosion protection mechanism of super-hydrophobic coatings are introduced firstly. Secondly, the fabrication methods by electrochemical surface engineering—including electrochemical anodization, micro-arc oxidation, electrochemical etching, and deposition—are presented. Finally, the stabilities and future directions of super-hydrophobic coatings are discussed in order to promote the movement of such coatings into real-world applications. The objective of this review is to bring a brief overview of the recent progress in the fabrication of super-hydrophobic coatings by electrochemical surface methods for corrosion protection of engineering materials.

Super-Hydrophobic Co–Ni Coating with High Abrasion Resistance Prepared by Electrodeposition

Although super-hydrophobic surfaces have great application prospects in industry, their preparation cost and mechanical durability have limited their practical utilization. In this work, we presented a new low-cost process preparation for super-hydrophobic Co–Ni coating on carbon steel substrate via an electrodeposition route. The deposited Co–Ni coating with cauliflower-shaped micro-nano structures exhibited high super-hydrophobic properties with water contact angles over 161° after modification with 1H,1H,2H,2H-Perfluorooctyltrichlorosilane (PFTEOS). Evaluated by the linear abrasion methods, the super-hydrophobic coating can maintain super-hydrophobicity after abrasion distance of 12 m under the applied pressure of 5 kPa, which was attributed to the high cobalt content of the Co–Ni coating. Moreover, electrochemical tests showed that the super-hydrophobic Co–Ni coatings exhibited a good anti-corrosion performance thus providing an adequate protection to the carbon steel substrates.

Droplet Impact on the Super-Hydrophobic Surface with Micro-Pillar Arrays Fabricated by Hybrid Laser Ablation and Silanization Process

A super-hydrophobic aluminum alloy surface with decorated pillar arrays was obtained by hybrid laser ablation and further silanization process. The as-prepared surface showed a high apparent contact angle of 158.2 ± 2.0° and low sliding angle of 3 ± 1°. Surface morphologies and surface chemistry were explored to obtain insights into the generation process of super-hydrophobicity. The main objective of this current work is to investigate the maximum spreading factor of water droplets impacting on the pillar-patterned super-hydrophobic surface based on the energy conservation concept. Although many previous studies have investigated the droplet impacting behavior on flat solid surfaces, the empirical models were proposed based on a few parameters including the Reynolds number (Re), Weber number (We), as well as the Ohnesorge number (Oh). This resulted in limitations for the super-hydrophobic surfaces due to the ignorance of the geometrical parameters of the pillars and viscous energy dissipation for liquid flow within the pillar arrays. In this paper, the maximum spreading factor was deduced from the perspective of energy balance, and the predicted results were in good agreement with our experimental results with a mean error of 4.99% and standard deviation of 0.10.

Is dropwise condensation feasible? A review on surface modifications for continuous dropwise condensation and a profitability analysis

The interest in surface treatments promoting dropwise condensation has grown exponentially in the past decades. Savings in the operating and maintenance costs of steam processes involving phase changes are promised. Numerous surface preparation methods allow the formation of droplets during condensation. However, stable dropwise condensation has been hardly realized in industrial applications. This review aims to highlight the surface preparation techniques that promote dropwise condensation. It emphasizes on their durability and the resulting stability of dropwise condensation. Furthermore, the possibilities of implementation at an industrial level are discussed, apart from evaluating the economic feasibility through a case study. Despite years of research and numerous surface design possibilities, dropwise condensation cannot be maintained: coating deterioration and fluctuating process conditions commonly lead to surface flooding within hours or weeks. A more profound understanding of the mechanisms of dropwise condensation and innovative design concepts for self-renewing heat transfer surfaces may diminish encountered challenges.

Thermally Robust Non-Wetting Ni-PTFE Electrodeposited Nanocomposite

The effect of high temperature exposure on the water wetting properties of co-electrodeposited superhydrophobic nickel-polytetrafluoroethylene (Ni-PTFE) nanocomposite coating on copper substrates was studied. This was accomplished by comparing the performance with a commercial superhydrophobic spray treatment (CSHST). The Ni-PTFE and CSHST coatings were both subjected to heating at temperatures up to 400 °C. Results showed that the Ni-PTFE was able to maintain its superhydrophobicity throughout the entire temperature range, whereas the CSHST became more wettable at 300 °C. Furthermore, additional abrasive wear tests were conducted on both materials that were subjected to heating at 400 °C. The Ni-PTFE remained highly non-wettable even after 60 m of abrasion length on 800 grit silicon carbide paper, whereas the CSHST coating was hydrophilic after 15 m.

A Rapid One-Step Process for Fabrication of Biomimetic Superhydrophobic Surfaces by Pulse Electrodeposition

Inspired by some typical plants such as lotus leaves, superhydrophobic surfaces are commonly prepared by a combination of low surface energy materials and hierarchical micro/nano structures. In this work, superhydrophobic surfaces on copper substrates were prepared by a rapid, facile one-step pulse electrodepositing process, with different duty ratios in an electrolyte containing lanthanum chloride (LaCl₃·6H₂O), myristic acid (CH₃(CH₂)₁₂COOH), and ethanol. The equivalent electrolytic time was only 10 min. The surface morphology, chemical composition and superhydrophobic property of the pulse electrodeposited surfaces were fully investigated with SEM, EDX, XRD, contact angle meter and time-lapse photographs of water droplets bouncing method. The results show that the as-prepared surfaces have micro/nano dual scale structures mainly consisting of La[CH₃(CH₂)₁₂COO]₃ crystals. The maximum water contact angle (WCA) is about 160.9°, and the corresponding sliding angle is about 5°. This method is time-saving and can be easily extended to other conductive materials, having a great potential for future applications.

Facile Preparation of a Robust and Durable Superhydrophobic Coating Using Biodegradable Lignin-Coated Cellulose Nanocrystal Particles

It is a challenge for a superhydrophobic coating to overcome the poor robustness and the rough surface structure that is usually built using inorganic particles that are difficult to degrade. In this study, a robust superhydrophobic coating is facilely prepared by using commercial biodegradable lignin-coated cellulose nanocrystal (L-CNC) particles after hydrophobic modification to build rough surface structures, and by choosing two different adhesives (double-sided tape and quick-setting epoxy) to support adhesion between the L-CNC particles and the substrates. In addition to excellent self-cleaning and water repellence properties, the resulting coatings show outstanding mechanical strength and durability against sandpaper abrasion, finger-wipe, knife-scratch, water jet, UV radiation, high temperature, and acidic and alkali solutions, possessing a wide application prospect.

Nature-Inspired Strategy toward Superhydrophobic Fabrics for Versatile Oil/Water Separation

Phytic acid, which is a naturally occurring component that is widely found in many plants, can strongly bond toxic mineral elements in the human body, because of its six phosphate groups. Some of the metal ions present the property of bonding with phytic acid to form insoluble coordination complexes aggregations, even at room temperature. Herein, a superhydrophobic cotton fabric was prepared using a novel and facile nature-inspired strategy that introduced phytic acid metal complex aggregations to generate rough hierarchical structures on a fabric surface, followed by PDMS modification. This superhydrophobic surface can be constructed not only on cotton fabric, but also on filter paper, polyethylene terephthalate (PET) fabric, and sponge. Ag^I, Fe^III, Ce^III, Zr^IV, and Sn^IV are very commendatory ions in our study. Taking phytic acid-Fe^III-based superhydrophobic fabric as an example, it showed excellent resistance to ultraviolet (UV) irradiation, high temperature, and organic solvent immersion, and it has good resistance to mechanical wear and abrasion. The superhydrophobic/superoleophilic fabric was successfully used to separate oil/water mixtures with separation efficiencies as high as 99.5%. We envision that these superantiwetting fabrics, modified with phytic acid-metal complexes and PDMS, are environmentally friendly, low cost, sustainable, and easy to scale up, and thereby exhibit great potentials in practical applications.

A study of enhanced ion formation from metal-semiconductor complexes in atmospheric pressure laser desorption/ionization mass spectrometry

The study of the key parameters impacted surface-assisted laser desorption/ionization-mass spectrometry is of broad interest. In previous studies, it has been shown that surface-assisted laser desorption/ionization-mass spectrometry is a complex process depending on multiple factors. In the presented study, we showed that neither porosity, light absorbance nor surface hydrophobicity alone influence the enhancement phenomena observed from the hybrid metal-semiconductor complexes versus individual targets, but small changes in the analyte attaching to the target significantly affect laser desorption ionization-efficiency. By means of Raman spectroscopy and scanning electron microscopy, it was revealed that the formation of an amorphous analyte layer after drying on a solid substrate was essential for the enhanced laser desorption ionization-signal observed from the hybrid metal-semiconductor targets, and the crystallization properties of the analyte appeared as a function of the substrate. Obtained results were used for the screening of regular and lactose-free milk samples through the hybrid metal-semiconductor target. Copyright © 2016 John Wiley & Sons, Ltd.

Nanostructured ZnO thin films for self-cleaning applications

Nanostructured ZnO films were deposited by wet chemical methods on glass substrates for self-cleaning applications.

Effect of Nano-TiC Dispersed Particles and Electro-Codeposition Parameters on Morphology and Structure of Hybrid Ni/TiC Nanocomposite Layers

This research work describes the effect of dispersed titanium carbide (TiC) nanoparticles into nickel plating bath on Ni/TiC nanostructured composite layers obtained by electro-codeposition. The surface morphology of Ni/TiC nanostructured composite layers was characterized by scanning electron microscopy (SEM). The composition of coatings and the incorporation percentage of TiC nanoparticles into Ni matrix were studied and estimated by using energy dispersive X-ray analysis (EDX). X-ray diffractometer (XRD) has been applied in order to investigate the phase structure as well as the corresponding relative texture coefficients of the composite layers. The results show that the concentration of nano-TiC particles added in the nickel electrolyte affects the inclusion percentage of TiC into Ni/TiC nano strucured layers, as well as the corresponding morphology, relative texture coefficients and thickness indicating an increasing tendency with the increasing concentration of nano-TiC concentration. By increasing the amount of TiC nanoparticles in the electrolyte, their incorporation into nickel matrix also increases. The hybrid Ni/nano-TiC composite layers obtained revealed a higher roughness and higher hardness; therefore, these layers are promising superhydrophobic surfaces for special application and could be more resistant to wear than the pure Ni layers.

Transition from amorphous to crystalline state for nickel electrodeposited from an ionic liquid

The microstructure of metallic nickel electrodeposited from an ionic liquid onto a copper substrate may be tuned and transition from amorphous to crystalline state can be achieved by regulating water content in the bath.