Superhydrophobic Silicone Rubber Research Articles

Effect of high directional convex structure on droplet morphology and contact angle

The morphology of a surface has certain influences on its wettability as reflected by the shape of a sessile droplet thereon. The topological structure of superhydrophobic silicone rubber (MVQ) prepared by template method has the characteristics of simple shape and regular arrangement, but such a structure will lead to unstable contact angle (CA) of superhydrophobic surface. Through this study, it is found that the CA value of the original flat MVQ surface is the same in any direction. However, from 0° to 90°, it is observed that the CA on the MVQ surface, the contact radius between water droplets and MVQ and the projected area of water droplets are different. In different directions, the maximum error of CA is 13.75°, the maximum error of contact radius between water droplets-MVQ is 209.5 μm, and the maximum error of projected area of water droplets is 0.284 mm2. In addition, it is found that the contact radius between water droplets and the surface of silicone rubber decreases with the increase of the projected area of water droplets in the direction of larger CA. In order to explain the error of CA and droplet shape due to directionality, this phenomenon is explained by micro-morphology and three-dimensional morphology combined with contact line density theory. This discovery is beneficial to design super-hydrophobic surface with high directionality and realize the application of micro-channel control technology.

Hydrophilic silica transformed silicone rubber into Superhydrophobic composites

AbstractSilicone rubber is widely used in medical and equipment manufacturing fields due to its excellent sealing and solvent resistance. However, the hydrophobicity of silicone rubber was unsatisfactory for many advanced engineering structures and applications. Generally, the preparation of artificial superhydrophobic materials suffered from either complicated in process or poor in environmental protection. Here, we reported a simple method to prepare silicone rubber composites with excellent superhydrophobic properties (water contact angle [WCA] = 155.2°) from low‐cost hydrophilic silica. Tests showed that the uniform micro‐nano structures were the key to the superhydrophobic properties of silicone rubber composites. The bounce test observed the rebound of water droplets with different initial velocities (0.77, 1, and 2 m/s) impacting silicone rubber surface, and verified the great advantages of silicone rubber modified by silica in hydrophobic. The modification method shown in this work provides a simple way to manufacture non‐fluorinated, robustness superhydrophobic surfaces for a wide range of potential applications.Highlights Based on the improvement of micro‐nano structure of the matrix surface by industrial silica, the preparation of superhydrophobic silicone rubber composites was realized. A process method for preparing fluorine‐free superhydrophobic silicone rubber composites from hydrophilic silica was proposed. Stretchability and robustness were the key factors for successful superhydrophobic modification of silicone rubber elastomers.

Superhydrophobic Flexible Silicone Rubber with Stable Performance, Anti-Icing, and Multilevel Rough Structure

Superhydrophobic surfaces made of flexible materials have attracted much attention in the fields of wearable and flexible devices. In this work, an easy-to-process, fluorine-free, mechanically stable superhydrophobic surface with a multilayered rough structure was fabricated by the template/spraying method using silicone rubber with mechanical flexibility, electrical insulation, and bio-inertness. It can form an air layer between the droplet and the sample, reducing the contact area between the droplet and the sample, and its contact angle can reach 170° and the rolling angle can be 2.5°. After many bendings and twistings, the sample still maintains excellent superhydrophobic performance. The contact angle of the sample still exceeded 150° after 100 cm of abrasion on the sandpaper. Droplets can bounce many times on the sample surface without being stuck. Compared with the control surface, the time from the beginning of precooling to the complete freezing of droplets on the superhydrophobic surface was extended by a factor of 3.4 at −10 °C. Therefore, this research still has a bright application prospect in extreme environments.

A high reliability super hydrophobic silicone rubber

Superhydrophobic surface is extensive used in aerospace, biomedicine and everyday life because of its excellent hydrophobicity. In order to verify the durability and stability of superhydrophobic silicone rubber composite (MVQ/screen mesh/spray) prepared by template method and spraying technology, dry heat aging test, acid and alkali salt resistance test, extrusion resistance test, steel ball resistance test and sandpaper wear test were carried out. The results showed that the surface contact angle of the prepared MVQ/screen mesh/spray was 160.88 ± 0.78°, and the rolling angle was 1°. After a series of durability tests, because of the regular concave-convex structure of the rubber surface, the abrasion of the rubber surface was slowed down, and when the liquid drops fell on the surface of MVQ/screen mesh/spray, it can provide great support and kept good hydrophobic effect on the rubber surface. The mechanism of rubber surface wettability was expounded, and the influence of chemical and physical factors on superhydrophobic surface was analyzed.

Preparation and analysis of conductive and superhydrophobic silicone rubber

Conductive and superhydrophobic rubber products are of great significance to the safety and long-term use of outdoor equipment. However, the preparation of low-cost conductive, superhydrophobic rubber products with good extensibility, durability, stability, and environmental adaptability remains a challenge. In this paper, conductive and superhydrophobic silicone rubber composites with uniform concave-convex structure were prepared on the surface of silicone rubber by filling carbon nanotubes (CNTs) in the silicone rubber matrix and using 2000 mesh screen template replication method and spraying technology. Using the self-made conductive circuit, the good electrical conductivity of the silicone rubber composite was verified at 200% elongation and after 500 times of torsion. In addition, the silicone rubber composite had good droplet bounce, anti-icing and self-cleaning properties.

Temperature-dependent droplet impact dynamics of a water droplet on hydrophobic and superhydrophobic surfaces: An experimental and predictive machine learning–based study

• Droplet impact on microstructured surfaces (hydrophobic/superhydrophobic) at different temperatures has been studied. • Effect of velocity, droplet diameter, temperature, surface wettability and roughness on impact dynamic are evaluated. • Using three machine-learning algorithms, an innovative method for predicting droplet impact dynamic is presented. Heightening the water repellency of surfaces can serve anti-icing purposes by removing water drops before they freeze and adhere to a surface. Here we study the impact dynamics of water droplets on silicone rubber surfaces—ranging from hydrophobic to superhydrophobic—at −20, −10, and 25 °C. We evaluate the influence of static contact angle, contact angle hysteresis, surface roughness, temperature, impacting velocity, and droplet diameter on droplet behavior (e.g., deposition, bouncing, splash). Minor effect of temperature on droplet dynamics on microstructured surfaces for a wide range of Weber and Reynolds numbers is observed. Experimental observations show that full bouncing only occurs on superhydrophobic surfaces with a CA > 160° and a CAH < 2° at temperatures above 0 °C for We < 110 and Re < 5000. Increasing the impact velocity of the droplet on rough surfaces heightens the probability of splashing. This experimental data is then coupled with machine-learning techniques (logistic regression, decision tree, and random forest) to comprehensively investigate droplet impact behavior on hydrophobic and superhydrophobic surfaces at various temperatures. We predict the behavior probability of impacting droplets on surfaces as a function of Weber number, Reynolds number and surface features (static contact angle, contact angle hysteresis, temperature, and surface roughness). Our experimental results and machine learning–based predictions are highly consistent, demonstrating that machine learning can effectively predict droplet motion on hydrophobic and superhydrophobic silicone rubber surfaces at different temperatures.

Laser etching-based surface wetting modulation of silicone rubber for triboelectric nanogenerator

Silicone rubber is a widely used functional material whose lifetime and safety properties can be improved by achieving superhydrophobicity on the surface. However, there are few studies on the use of superhydrophobic surfaces as nano-energy devices. In this work, laser etching was used to achieve continuous regulation of the superhydrophobic to superhydrophilic state of the surface on silicone rubber. The modulation of wettability is attributed to laser manufactured micro-nanostructures, while the laser can be used to recover the damaged structures. Meanwhile, a triboelectric nanogenerator (TENG) is fabricated using superhydrophobic silicone rubber and drives the LED to light up. In short, this study provides a simple solution for TENG and its recycling.

Electrical Utilizations of Air Gap Region Formed on Superhydrophobic Silicone Rubber in NaCl Aqueous Solution

A uniform air gap was successfully formed on a superhydrophobic silicone rubber in water or NaCl aqueous solution. The main chain of Si–O bonds of a silicone rubber was photodissociated by a 193 nm ArF excimer laser to lower the molecular weight only in the laser-irradiated microareas; due to the volume expansion, the microswelling structure was periodically fabricated on a silicone rubber, showing the superhydrophobic property. A pair of metal needles were inserted in the air gap formed on the superhydrophobic silicone rubber in a NaCl aqueous solution; an electrical insulation between two metal needles in the air gap was demonstrated. Additionally, a droplet of NaCl aqueous solution was confined in the air gap, after which the pair of metal needles contacted with the droplet through the air gap. As a result, an electrolysis of the droplet of NaCl aqueous solution occurred to produce hydrogen gas on the cathode in the air gap. Moreover, when Al and Cu wires were provided across the air gap and NaCl aqueous solution on the superhydrophobic silicone rubber, approximately 0.8–0.9 V of electric voltage was successfully generated between the two wires in the air gap based on the difference in electrochemical potential as an energy harvesting device in the sea.

Laser direct writing of a multifunctional superhydrophobic composite strain sensor with excellent corrosion resistance and Anti-Icing/Deicing performance

Superhydrophobic composite strain sensors have attracted extensive attention due to their excellent waterproof, anti-icing, flexible and conductive properties, but there are still challenges to prepare it with broad sensing range, superior sensitivity, stable superhydrophobicity, and excellent long-term stability. In this study, we developed a multifunctional superhydrophobic silicone rubber (SR)/multi-walled carbon nanotubes (MWCNTs)/laser-induced graphene (LIG)/SR composite strain sensor using laser direct writing. A highly stable MWCNTs/LIG crosslinked conductive network layer, high-performance superhydrophobic layer, and stretchable SR layer were integrated to fabricate the sensor by tuning the laser parameters. The SR/MWCNTs/LIG/SR composite strain sensor possessed a high gauge factor of 667, large strain detection range of 0–230%, and a stable sensing response over 2500 cycles due to the MWCNTs/LIG crosslinked conductive network. Moreover, the SR/MWCNTs/LIG/SR composite strain sensor could effectively prevent icing owing to its anti-icing (36 min@-5 °C) and photothermal deicing (88 s@1 W/cm2@NIL) properties and hinder acid and alkaline (pH = 1–14) corrosion attributed to the laser-induced superhydrophobicity, thereby expanding its applications to acid, alkaline, and low-temperature environments. Consequently, the multifunctional superhydrophobic SR/MWCNTs/LIG/SR composite strain sensor is demonstrated to be suitable for human body motion detection in complex and severe environments.

Aging Characteristics of Superhydrophobic Silicone Rubber Surfaces Etched by Femtosecond Laser

Aging Characteristics of Superhydrophobic Silicone Rubber Surfaces Etched by Femtosecond Laser

Aging characteristics and self-healing properties of laser-textured superhydrophobic silicone rubber for composite insulators

The aging characteristics of laser-treated superhydrophobic silicone rubber surfaces was investigated through accelerated aging tests. It indicated that the superhydrophobic surfaces have excellent anti-aging properties, which is manifested in that even after aging for 1000 h, the contact angles of the superhydrophobic surfaces remain above 140o. The loss of hydrophobicity was caused by defects in the surface microstructures, a decrease in the hydrophobic ―CH3 groups, and an increase in the hydrophilic ―OH groups on the surfaces. To avoid the decrease in the hydrophobicity of the prepared superhydrophobic surface, a simple and efficient heat treatment method was adopted to restore its hydrophobicity. After heat treatment at 200°C, the rolling angle of the aged surface was restored to 4.6o with a contact angle of 161.5o. This recovery is mainly attributed to the decrease in the content of the ―OH on the rubber surface during the heat treatment. The results also show the sample surface irradiated with a laser fluence of 10.0 J/cm2 has better anti-aging performance and self-healing properties due to the larger particles and a more distinct micro-nano hierarchical structures, providing a smaller actual illumination area and a larger heating area in the aging and heat treatment process.

纳秒激光诱导超疏水硅橡胶表面微结构的分形特性

纳秒激光诱导超疏水硅橡胶表面微结构的分形特性

Study on preparation and properties of superhydrophobic surface of RTV silicone rubber

Silica (SiO2) powder and physical deposition technique were performed to fabricate superhydrophobic silicone rubber (SR) surfaces, and the contact angle and the rolling angle were 160.3 ± 1.0° and 2.8 ± 0.3°, respectively (the contact angle and the rolling angle of the original surface of the SR were 130 ± 1.8° and 36.7 ± 0.8°, respectively). The surface roughness of the sample was measured by interferometric three-dimensional topography profiler, and the results showed that the surface roughness increased after being treated by SiO2. A self-cleaning test was designed to verify the self-cleaning effect of the sample surface. Besides, a scanning electron microscope (SEM) was employed to observe the microstructure of the sample surface and the dispersion of SiO2, and energy dispersive spectroscopy (EDS) was utilized to determine the element composition and content of the sample surface. In order to further demonstrate the superhydrophobic property of the surface of the sample, the horizontal bouncing test at room temperature (25 °C) and the tilted bouncing test at an angle of 10° with the horizontal plane were carried out, and it was found that the sample had remarkable bouncing performance. Moreover, high temperature bounce tests were performed to investigate the stability of the surface superhydrophobic property of the sample, indicating that the sample had significant high temperature resistance.

A fluorine-free superhydrophobic silicone rubber surface has excellent self-cleaning and bouncing properties

Superhydrophobic materials have been widely applied in self-cleaning, anti-fouling, anti-corrosion, anti-freezing. However, simple, efficient, environmentally friendly and large-area preparation is still a great challenge in the field of fabrication of superhydrophobic surfaces. In this paper, a simple physical deposition method is adopted to deposit a layer of alumina oxide (Al2O3) particles on the surface of the room temperature vulcanized (RTV) silicone rubber, and remove the excess Al2O3 particles on the surface to obtain the superhydrophobic surface of Al2O3/RTV silicone rubber. The contact angle and rolling angle of the superhydrophobic surface are 156.6° ± 1.1° and 5.1° ± 0.7°, respectively. It is found that the surface roughness of RTV silicone rubber is significantly increased via Al2O3 particles. The analysis of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) demonstrate that the superhydrophobic surface is obtained via constructing rough structure of Al2O3 particles on the RTV silicone rubber surface. In addition, the self-cleaning and droplet bounce tests under different conditions show that the as-prepared superhydrophobic surface has remarkable self-cleaning and droplet bounce properties. Therefore, this method can be employed to simply and effectively fabricate superhydrophobic surfaces in large scale.

A Review on Fabrication Methods and Research Progress of Superhydrophobic Silicone Rubber Materials

AbstractSilicone rubber materials have excellent comprehensive properties and are widely used in outdoor insulation, aerospace, and other fields. Due to its low surface energy and the appearance of biomimetic superhydrophobic materials, silicone rubber has become one of the popular materials in the field of superhydrophobicity. Superhydrophobic silicone rubber materials play an irreplaceable role in a wide range of applications such as long‐distance high‐voltage power transmission and high‐speed rail transportation. In this paper, research on superhydrophobic materials, including typical fabrication methods, is summarized to provide an overview of the up‐to‐date research state and progress in detail.

Icephobicity and durability assessment of superhydrophobic surfaces: The role of surface roughness and the ice adhesion measurement technique

The durability of anti-wetting properties is of great importance for ensuring long-lasting superhydrophobic and icephobic surfaces that require minimal maintenance and resurfacing. Herein, we fabricated superhydrophobic silicone rubber surfaces having ultra-water repellency and icephobic properties via two industrially applicable methods: micro compression molding (μCM) and atmospheric pressure plasma (APP) treatment. We produced surfaces covered by micro-nanostructures of differing sizes. We evaluated the anti-icing properties (delayed ice formation) and de-icing properties (reduced ice adhesion strength) of the produced surfaces that were subjected to two forms of icing conditions. The well-known ice adhesion measurement techniques, i.e., the centrifuge adhesion and push-off tests, provided quantitative comparisons of the ice adhesion strength of the produced surfaces. We observed two different mechanical deformations during the ice detachment from the surfaces. Although both superhydrophobic surfaces reduced ice adhesion strength, the smaller surface micro-nanostructures produced a greater reduction in ice adhesion by favoring less ice interlocking with the surface asperities. To rigorously assess the durability of the produced surfaces, we carried out a comprehensive series of experiments that covered a wide range of real-life conditions. Under harsh environmental conditions, the surfaces maintained a water contact angle and contact angle hysteresis of >150° and <10°, respectively, thereby confirming the resistance of the superhydrophobic silicone surfaces to severe chemical and mechanical damage. In some cases where water repellency was lost, the silicone rubber surfaces demonstrated a satisfactory recovery of their anti-wetting properties.

Superhydrophobic silicone rubber surface prepared by direct replication

ABSTRACT The superhydrophobic surface of silicone rubber was prepared by means of a simple direct replication and compression moulding process. It was worth noting that the rough structure endowed the surface of the silicone rubber with excellent superhydrophobic, low adhesion and self-cleaning properties. The contact angle with water was 158.5 ± 0.5°, and the rolling angle was 8.9 ± 0.1°. Even if immersed in water, the surface will not become wetted by the water. In addition, it has excellent properties of hydrophobic hydrochloric acid solution, sodium hydroxide solution and sodium chloride solution. Through a high-speed camera, it was found that water droplets would bounce up after falling on the superhydrophobic surface of the silicone rubber. When the liquid drops fall perpendicular to the superhydrophobic surface of silicone rubber, the time of contact between the liquid drops and the superhydrophobic surface is not inversely proportional to the height of the drop falling.

Fabrication of self-cleaning superhydrophobic silicone rubber insulator through laser texturing

ABSTRACT Silicone insulators are gaining its importance in the transmission and distribution of the power system networks. This study proposes a simple and high throughput way of fabrication of superhydrophobic silicone surfaces. The Nd:YAG nanosecond pulse laser was used to engrave six different types of structures on silicone rubber. The water contact angle (CA) and contact angle hysteresis (CAH) were measured using drop shape analyser goniometer. The self-cleaning property of the structured silicone surfaces was tested. Among six types of patterns, the structures formed through 50% scanning overlapped possess high CA (159 ± 1°) with very low CAH (3°) which is desirable for any self-cleaning surface. However, a completely irradiated silicone surface gives the highest CA (163 ± 2°) with very high CAH (61.84°). The proposed work is a vital step towards making a superhydrophobic insulator surface without the use of any coating for high voltage power system applications.

A superhydrophobic surface with aging resistance, excellent mechanical restorablity and droplet bounce properties.

The use of a silicone rubber composite insulator has become an important aspect to ensure the safe operation of an electrical power grid. This study introduces a preparation method of a superhydrophobic silicone rubber surface using a simple preparation process at low cost and with excellent performance, which can be used in the mass production of silicone rubber composite insulators. In this study, the combination of a compression molding process and a template method was used to prepare the product. A microstructure composed of numerous boat-shaped grooves was constructed on the surface of silicone rubber. The modification of a low surface energy material is not required. The static contact angle with water after the high-temperature treatment exceeds 150°, and the rolling angle is under 10°. Excellent performance has been observed in terms of self-cleaning effect, aging resistance, and mechanical and droplet bounce properties. It has been shown that the loss of superhydrophobic properties, due to the prolonged immersion in water, can be restored by a high temperature heating process.

Icing performance of superhydrophobic silicone rubber surfaces by laser texturing

In this paper, the superhydrophobic surfaces of silicone rubber with different microstructure were directly prepared by texturing with a nanosecond fibre laser. The superhydrophobic surfaces have excellent anti-icing performance. Even at 0 °C, the superhydrophobic surface has a contact angle of ∼150° and a rolling-off angle of ∼2.5°. The superhydrophobic silicone rubber surfaces with different microstructures have obvious differences in contact behaviours with water droplets at low temperatures. The surface textured with a laser fluence of 10 J cm−2 has a larger particle size and more abundant micro-nano particles, which results in a smaller contact area with the water droplet due to greater roughness and root mean square slope. The deeper the small gaps on the superhydrophobic surface, the more time it takes for the change in contact state between the surface and the water droplets. The adhesion strength of the superhydrophobic rubber surfaces with the ice layer were smaller due to the air stored between the surfaces and the ice layer. In particular, the laser textured surface with an laser fluence of 10 J cm−2 has the lowest ice adhesion strength due to its layered micro-nano composite structure. After 30 cycles of icing and de-icing, the processed silicone rubber surface still retains excellent hydrophobicity. The superhydrophobic silicone rubber surface has important value in anti-icing and anti-pollution applications.