Low Adhesion Surfaces Research Articles

Study on nano-graphitic carbon coating on Si mold insert for precision glass molding

Precision glass molding is an efficient and promising technique for large-volume micro-optical manufacturing. Even though significant progress in precision glass molding has been achieved on the anti-adhesive coating, technical challenges and barriers still exist towards tailoring the coating layer to ensure durability and long-term processing consistency in numerous molding cycles. This manuscript presents a novel molding technique utilizing micro-patterned Si mold inserts coated with a newly developed nano-graphitic carbon coating as an isolation layer in high-precision glass molding. The coating is prepared by atmospheric pressure chemical vapor deposition (APCVD), in which the liquid benzene and silicone rubber are used as the carbon source and silicon oxycarbide (SiOC) source, respectively. The nano-morphologies of the nano-graphitic carbon coating with different conditions are characterized and analyzed, illustrating notable differences in surface features with the addition of silicone rubber and various growth durations. In the demonstration, the nano-graphitic carbon-coated Si mold inserts exhibit unique properties, including anti-adhesive and hydrophobic at elevated temperatures. Two kinds of micro-patterned Si mold inserts, a micro-pillar matrix and a micro-lens array, generated by UV lithography and diamond turning, are utilized to demonstrate the feasibility of the anti-adhesive coating in precision glass molding. The obtained results indicate that the micro-optical features on the coated Si mold inserts are successfully transferred to glass substrates with high replication fidelity without notable signs of adhesion or contamination in repetitive molding cycles. This emerging technology makes Si an alternative mold material with low surface adhesion, enhances micro-optical machining efficiency, and replicates high-precision, low-cost micro-optics on large scales that were previously unavailable.

Low adhesive and superhydrophobic LDH coating for anti-corrosion and self-cleaning

Superhydrophobic coatings show wide applications. Here, a low adhesive superhydrophobic surface was prepared by an in-situ growth of layered double hydroxide (LDH) combined with a surface modification process by stearic acid (STA). The LDH sheets provide a rough structure and the STA molecule provides the low surface energy. As results, the STA-LDH coating shows a water contact angle of 151°. The siliding angle of the STA-LDH coating is less than 5°. Besides, the coating shows a low-adhesive surface with good self-cleaning property. Electrochemical tests confirms that the STA-LDH coating shows elevated coating resistance from 5.105 × 104 Ω·cm2 for bare sample to 8.46 × 106 Ω·cm2. Furthermore, the corrosion current density of the STA-LDH coating decreases by ~2 orders of magnitude compared to the bare Al alloy. This work provide a novel strategy for constructing low-adhesive, self-cleaning and anticorrosive coating.

Stable dispersibility of bentonite-type additive with gemini ionic liquid intercalation structure for oil-based drilling

In this study, the direct intercalation of gemini ionic liquids (ILs) with different alkyl chains into the bentonite (BT) interlayer as a high-performance lubricating additive for base oil 500SN was investigated. The purpose of modifying BT with an IL is to improve the dispersion stability and lubricity of BT in lubricating oil. The dispersibility and tribological properties of IL—BT as oil-based additives for 500SN depend on the increase in interlamellar space in BT and improve as the chain length is increased. More importantly, the IL—BT nanomaterial outperforms individual BT in improving wear resistance, owing to its sheet layers were deformed and sprawled in furrows along the metal surface, thereby resulting in low surface adhesion. Because of its excellent lubrication performance, IL-modified BT is a potential candidate for the main component of drilling fluid. It can be used as a lubricating additive in oil drilling and oil well construction to reduce equipment damage and ensure the normal operation of equipments.

Assembly of Graphene Platelets for Bioinspired, Stimuli-Responsive, Low Ice Adhesion Surfaces.

Design and fabrication of functional materials for anti-icing and deicing attract great attention from both the academic research and industry. Among them, the study of fish-scale-like materials has proved that enabling sequential rupture is an effective approach for weakening the intrinsic interface adhesion. Here, graphene platelets were utilized to construct fish-scale-like surfaces for easy ice detachment. Using a biomimicking arrangement of the graphene platelets, the surfaces were able to alter their structural morphology for the sequential rupture in response to external forces. With different packing densities of graphene platelets, all the surfaces showed universally at least 50% reduction in atomistic tensile ice adhesion strength. Because of the effect of sequential rupture, stronger ice–surface interactions did not lead to an obvious increase in ice adhesion. Interestingly, the high packing density of graphene platelets resulted in stable and reversible surface morphology in cyclic tensile and shearing tests, and subsequently high reproducibility of the sequential rupture mode. The fish-scale-like surfaces built and tested, together with the nanoscale deicing results, provided a close view of ice adhesion mechanics, which can promote future bioinspired, stress-responsive, anti-icing surface designs.

Tunable Adhesion and Interfacial Structure of Layer‐by‐Layer Assembled Block co‐polymer Micelle and Polyelectrolyte Coatings

AbstractUnderstanding and tuning nanoscale structure is critical in developing new coatings and adhesives. In this work layer‐by‐layer assembly of block co‐polymer (BCP) micelles and oppositely charged polyelectrolytes produces structurally unique coatings with wet adhesion comparable to that of mussel adhesive proteins. Cationic (CAT) and anionic (ANI) BCPs, synthesized by atom transfer radical polymerization (ATRP), are used to create colloidally stable, self‐assembled, spherical BCP micelles. The assembly of BCP micelle and polyelectrolyte multilayers is monitored in situ where CAT‐ and ANI‐BCP micelles exhibit linear and super‐linear growth, respectively. Imaging of the surfaces reveals that CAT‐BCP micelles yield flat, uniform layers whereas ANI‐BCP micelle assemblies form islands that increase in surface area with each additional layer. The adhesion of these layers, measured by colloidal probe atomic force microscopy (CP‐AFM), shows that the distinct layers of CAT‐BCP micelle assemblies produce alternating high and low adhesion surfaces whereas ANI‐BCP micelle assemblies continually increase in adhesion with each additional bilayer. The unique behavior of each assembly demonstrates that both composition and structure play important roles in wet adhesion of submicron layers and that each can be tuned to target performance for different applications.

Tunable and Robust Nanostructuring for Multifunctional Metal Additively Manufactured Interfaces.

Novel processing phenomena coupled with various alloying materials used in metal additive manufacturing (AM) have opened opportunities for the development of previously unexplored micro-/nanostructures. A rationally devised structure nanofabrication strategy of AM surfaces that can tailor the interface morphology and chemistry has the potential for many applications. Here, through an understanding of grain formation mechanisms during AM, we develop a facile method for tuning micro-/nanostructures of one of the most used AM alloys and rationally optimize the morphology for applications requiring low surface adhesion. We demonstrate that optimized AM structures reduce the adhesion of impaling water droplets and significantly delay icing time. The structure can also be altered and optimized for antiflooding jumping-droplet condensation that exhibits significant enhancement in heat transfer performance in comparison to nanostructures formed on conventional Al alloys. In addition to demonstrating the potential of functionalized AM surfaces, this work also provides guidelines for surface-structuring optimization applicable to other AM metals.

Parameter Study for the Ice Adhesion Centrifuge Test

In this study, we assessed the effects of ice types, test parameters, and surface properties on measurement data of the ice adhesion centrifuge test. This method is often used for the evaluation of low ice adhesion surfaces, although no test standard has been defined yet. The aim of this paper is to improve the understanding of the relevant test parameter and identify crucial criteria to be considered in harmonization and standardization efforts. Results clearly indicate that the ice type (static vs. impact ice) has the greatest impact on the test results, with static ice delivering higher values in a broader data span. This is beneficial for material developers as it eases the evaluation process, but it contradicts the technical efforts to design tests that are as close as possible to realistic technical environments. Additionally, the selected ice type has a significant impact on the relevance of the surface properties (roughness, wettability). Despite the complexity of interactions, a trend was observed that the roughness is the determining surface parameter for high impact velocity ice (95 m/s). In contrast, for tests with static ice, the wettability of the test surface is of higher relevance, leading to the risk of overestimating the icephobic performance of structured surfaces. The results of this paper contribute to the demanding future tasks of defining well-founded test standards and support the development of icephobic surfaces.

DEVELOPMENT AND CHARACTERISATION OF 3D SOLID TUMOUR CELL MODELS FOR INDIVIDUALIZED CANCER TREATMENT

Background. To solve the problems of personalized medicine in oncology, preclinical studies based on the use of three-dimensional cellular models of tumors in vitro, including spheroids / tumoroids, are of great importance. They are an interesting tool for genetic, epigenetic, biomedical and pharmacological studies aiming to determine the most effective individual therapeutic approaches, since they allow modeling the dynamic evolution of a tumor disease from early stages to metastatic spread through interaction with the microenvironment.The purpose of the study was to compare characteristic features of formation and spatial organization of spheroids, obtained from solid malignant tumors cells with various histogenesis: melanomas, soft tissue sarcomas and osteosarcomas, epithelial tumors.Material and Methods. Solid tumor cell lines of patients who were treated from 2015 to 2021 were the basis for the creation of 3D-cell models. Fragments of tumor tissue were obtained intraoperatively: 15 samples of melanoma, 20 samples of soft tissue sarcomas and osteosarcomas, and 9 samples of epithelial tumors. All tumor cells were cultured for at least 10 passages. Methods of phase contrast, confocal microscopy, and histological techniques were used to study spheroids. Using ELISA methods and multiplex analysis, the supernatants of monolayer cell cultures and spheroids were studied for the presence of a wide range of biologically active substances that provide the processes of immunosuppression, invasion and metastasis.Results. The use of low adhesion surfaces was proven to be preferable to obtain spheroids of a given seed concentration and size of interest. The average cultivation time of spheroids was 4.7 days, and the optimal seeding concentration was 10,000 cells per well, while the spheroid diameter varied from 300 to 1000 μm depending on the type of malignant cells: the largest spheroids formed melanoma cultures. In general, the efficiency of spheroid formation was 88.6 % (39 out of 44). The introduction of fibroblasts into the 3D construct led to increasing in the invasive potential of tumor cells, which was associated with the production of IL8 (rho=0.636, p=0.035), HGF (rho=0.850, p=0.004), SCF (rho=0.857, p=0.014), FST (rho=0.685, p=0.029), Prolactin (rho=0.810, p=0.015), PECAM1 (rho=0.788, p=0.004).Conclusion. The technology of low-adhesive surfaces makes it possible to successfully create three-dimensional models of a tumor node from malignant tumors cells of various histogenesis. The colonization of a three-dimensional structure with fibroblasts enhances the biologically aggressive properties of tumor cells and demonstrates complex reciprocal interactions between the cellular elements of the tumor stroma and malignant cells, which brings the model closer to a real clinical situation.

One-level microstructure-arrayed hydrophobic surface with low surface adhesion and strong anti-wetting function

To achieve both a low surface adhesion function and a high anti-wetting function, it is generally necessary to introduce multi-level micro–nano-structures on a surface. However, this will bring the difficulty of preparation technology, and the functions will fail due to the fact that the nanostructures can easily be damaged. In this research, the surface adhesion and anti-wetting properties of several typically one-level microstructure-arrayed hydrophobic surfaces are analyzed with the dynamics theory, including a square pillar-arrayed three-dimensional microstructure, a conical table-arrayed microstructure, and square frustum-arrayed microstructure. It is found that the anti-adhesion performance and anti-wetting property cannot achieve the best performance simultaneously on the one-level microstructure arrayed surfaces. Either the critical pressure of anti-wetting is finite when the surface adhesion is the lowest, or both the anti-adhesion and anti-wetting capacities are finite. However, an interesting phenomenon is found in that the square frustum-arrayed surface can not only achieve an almost infinite anti-wetting capacity when the distance between neighboring microstructures vanishes, but also reach near-zero adhesion when the square frustum reduces to a square pyramid. All the theoretical predictions are further verified by precise numerical simulations. The results of this paper should be helpful for the design of surfaces with low surface adhesion and strong anti-wetting functions in practical engineering.

Robust Control Design of Active Front-Wheel Steering on Low-Adhesion Road Surfaces

In order to improve the stability of vehicle steering on low-adhesion road surfaces, this paper designed a hybrid robust control strategy, H2/H∞, for active front-wheel steering (AFS) based on robust control theory. Firstly, we analyzed the influence of the sidewall stiffness and road adhesion coefficient of the tires on vehicle stability, through which we can study the wheel deflection characteristics of low-adhesion roads. Secondly, the reference yaw velocity of the vehicle was calculated using the three-degrees-of-freedom model as the reference model, through which, taking the norm H∞ as the objective function and the norm H2 as the limit to control the output, the hybrid robust control strategy H2/H∞ of the AFS system on a low-adhesion road surface was developed. Finally, the simulation experiment was carried out by the Simulink/CarSim co-simulation platform and a hardware-in-the-loop (HIL) experiment. In this paper, the results show that the AFS control strategy can improve the vehicle handling stability on low-adhesion road surfaces, and the controller has good path tracking performance and robustness.

Stable Nonwetting Artificial Compound Eye with Low Adhesion.

Microlens arrays (MLAs) are the key components of miniaturized optical systems. To meet the stringent requirements for their application in humid environments, achieving waterproof properties in these objects is an urgent task. It is noteworthy that conventional methods of microlens production usually sacrifice optical performance for stable superhydrophobicity by increasing the surface roughness of the microlens. In this paper, a large area artificial compound eye (ACE) is efficiently fabricated by combining photolithography and inkjet printing. The added micropillars separated the outside droplet from the microlens, and the water droplet was afterward suspended on the top of micropillars. Furthermore, the micropillars enabled superhydrophobicity (at a contact angle above 150°) and low surface adhesion (at a sliding angle of ∼2.8°) of the microlens without affecting its optical performance. Furthermore, when released from the height of 1 and 2 cm, the droplets were fully detached from the surface without sticking. The surface of the ACE was shown to have relatively stable nonwettability due to a small spacing between the micropillars. This means that tuning the morphology and spacing between micropillars allows one to noticeably improve the surface nonwettability stability. Finally, the performance of the fabricated optical system was demonstrated in a water washing experiment. Therefore, the findings of present study may open up the prospects for significant advancement in superhydrophobicity of the optical systems without affecting their imaging performance for real outdoor applications.

Inherently UV Photodegradable Poly(methacrylate) Gels

AbstractOrganogels (hydrophobic polymer gels) are soft materials based on polymeric networks swollen in organic solvents. They are hydrophobic and possess a high content of solvent and low surface adhesion, rendering them interesting in applications such as encapsulants, drug delivery, actuators, slippery surfaces (self‐cleaning, anti‐waxing, anti‐bacterial), or for oil‐water separation. To design functional organogels, strategies to control their shape and surface structure are required. Herein, the inherent UV photodegradability of poly(methacrylate) organogels is reported. No additional photosensitizers are required to efficiently degrade organogels (d ≈ 1 mm) on the minute scale. A low UV absorbance and a high swelling ability of the solvent infusing the organogel are found to be beneficial for fast photodegradation, which is expected to be transferrable to other gel photochemistry. Organogel arrays, films, and structured organogel surfaces are prepared, and their extraction ability and slippery properties are examined. Films of inherently photodegradable organogels on copper circuit boards serve as the first ever positive gel photoresist. Spatially photodegraded organogel films protect or reveal copper surfaces against an etchant (FeCl3 aq.).

Controlled Integration of Interconnected Pores under Polymeric Surfaces for Low Adhesion and Antiscaling Performance.

Low-adhesive surfaces have been highlighted due to the potentials to mitigate fouling issues by preventing unwanted substances from adhering. Realizing superhydrophobicity with 3D surface structures/chemical modifiers or fabricating lubricant-assisted slippery surfaces has been demonstrated to realize low-adhesive surfaces. However, they still need to overcome the transition to Wenzel from Cassie states of droplets on 3D surface structures or the lubricant depletion issues of slippery surfaces for sustainable operations. Herein, we report the fabrication of low-adhesive polymeric surfaces, neither assisted by 3D surface structures/chemical modifiers nor lubricants, which is realized by embedding the interconnected pore networks underneath the top smooth surface using a water steaming method. The fabricated silicone surfaces exhibit low-adhesive properties due to the stress concentration effects generated by the subsurface-structured pores, favorable for easy detachment of the adherent from the surface. Our platform can be exploited to lower adhesion of superhydrophilic surfaces or to achieve ultralow-adhesive properties upon combination with superhydrophobicity. Finally, scale precipitation tests reveal 4.2 times lower scale accumulation of our low-adhesive polymeric surfaces than that in control samples.

Slippery liquid-infused porous surfaces with inclined microstructures to enhance durable anti-biofouling performances

In the development of biocompatible materials for biomedical applications, infections and their resulting inflammation responses are important issues caused typically by the adhesion of micro-organisms on medical devices. Recently slippery liquid-infused porous surfaces (SLIPS) has provided a new strategy for anti-biofouling and low-adhesion surfaces, however, there are still some bottlenecks in practical uses, particularly the loss of lubricant significantly restricts the durability and stability of SLIPS. In this paper, we micro-fabricated well-controlled micro-cavities with different profiles (vertical or inclined walls) to investigate the long-term anti-biofouling effect of SLIPS. We explored microstructure geometries in two aspects: the aspect ratio and the slope angle relevant with the Laplace pressure and the oil contact area which lead to different oil-locking abilities. High aspect ratio and inclined slope were demonstrated with better oil-locking ability as well as significantly increased anti-fouling performances. Under the same experimental setup, the Escherichia coli and Staphylococcus aureus bacteria coverage on SLIPS with 80 μm-depth 20° inclined micro-cavities was only ∼30 % of that with vertical micro-cavities, while increasing aspect ratio by 4 times induced ∼3 times enhanced anti-fouling effect. On basis of these findings, we propose the enhanced SLIPS with inclined microstructures to achieve better oil-locking ability and long-term anti-biofouling performance, which may broaden many practical applications of SLIPS.

Facile one-step hydrothermal fabrication of Allium giganteum-like superhydrophobic coating on Mg alloy with self-cleaning and anti-corrosion properties

Superhydrophobic coating can act as the anti-corrosion layer for Mg alloy due to its water-repellency. The construction of such coating is dominated by the roughness and surface energy, which is expected to achieve in one-step to improve the weak adsorption phenomenon of surface modification during traditional approaches. Therefore, a superhydrophobic coating composed of CeO2 and cerium stearate (Ce(CH3(CH2)16COO)3) is fabricated via a facile hydrothermal method. The synthesis of Ce(CH3(CH2)16COO)3 passivates the surface of CeO2 nanosheets, leading to a reduction of surface energy and the formation of an Allium giganteum-like structure which presents a micro-nano hierarchical roughness. This unique structure with high roughness and low surface energy is responsible for the excellent superhydrophobic behavior of coating which has high water contact angle (WCA) of 164° and low rolling angle (RA) of 4.1°. The superhydrophobic coating also displays an outstanding self-cleaning behavior due to its low surface adhesion. The corrosion rate of prepared coating in 3.5 wt% NaCl aqueous solution is approximately two orders of magnitude lower than that of bare Mg alloy. This remarkably enhanced corrosion resistance arises from the decrease in contact area between the corrosion solution and sample due to the water-repellency of coating.

Low Ice Adhesion Surfaces Based on Flexible Fluorinated Polymers with a Polynorbornene Backbone.

Realizing icephobic surfaces with low ice adhesion and durability continues to be fascinating as well as challenging. Herein, a norbornene-based fluorinated polymer (NFP) with high flexibility and high tensile strength is designed and fabricated using a fluorinated side chain and a norbornene backbone, displaying low ice shear strength less than 20 kPa and excellent durability. Experimental and theoretical analyses show that the flexibility of the polymer chains and the synergistic macromolecular aggregation of the fluorinated side groups and the norbornene backbone play key roles in the excellent surface icephobic properties of the NFP films. Moreover, we also develop a facile approach to the design of durable icephobic slippery surfaces, which possess remarkable icephobic performance. This study not only sheds light on the relationship between the polymer molecular structure and surface icephobic properties but also provides a new avenue to conveniently realize anti-icing coatings.

A Fluoride‐Free and Super‐Wetting Functionalized‐Material with pH‐Responsiveness for Controllable Separation of Multiphase Oil/Water Mixtures

Nowadays, oily wastewater seriously endangers human health and living environment. Intelligent materials with switchable wettability gear up the broad application prospect in controllable oil/water separation and have received extensive attention. Herein, a simple and novel fluoride‐free method for preparing pH‐responsive super‐wetting material by monomer polymerization is reported. Surprisingly, the as‐prepared smart material can produce reversible wettability changes between superhydrophobicity/superoleophilicity and superhydrophilicity/underwater superoleophobicity by adjusting various pH values. Based on this fresh phenomenon, it can be used to separate various oil/water mixtures on‐demand with high separation performance. It is worth noting that the smart fabric also separates mixtures of highly corrosive liquids and oils. Moreover, the smart fabric also has excellent self‐cleaning and low surface adhesion. In addition, it also shows excellent mechanical and chemical stability under harsh conditions. All these advantages show that the smart fabric can play a vital function in solving the related severe conditions of marine oil pollution and industrial wastewater.

Highly stable superamphiphobic material with ethanol-triggered switchable wettability for high-efficiency on-demand oil–water separation

A large quantity of oil spills occurred have greatly endangered the natural environment and human survival health. Super-wetting materials with switchable wettability provide a good way to solve these problems efficiently and have been paid more and more attention. In this paper, we have successfully prepared an ethanol-triggered and highly stable superamphiphobic material with a switchable surface wettability by using zinc oxide (ZnO) particles and organic silane (PFDS) via a simple coating method. The superamphiphobic material can maintain high oil-repellent and water-repellent performances under various harsh conditions. Most importantly, the superamphiphobic material demonstrates the switchable wettability by ethanol treatment. In view of this fresh mechanism, it can separate various oil–water mixtures on-demand with high separation efficiency and flux. Surprisingly, the mixtures of highly corrosive liquids and oils can also be separated. In addition, the material also has excellent self-cleaning and anti-fouling capabilities and low surface adhesion, which can effectively avoid the pollution of pollutants in the air. All these advantages show that the as-prepared material can play a vital function in solving the related severe conditions of marine oil pollution and industrial wastewater.

Perfluoropolyether-benzophenone as a highly durable, broadband anti-reflection, and anti-contamination coating

Anti-reflection and anti-contamination coatings prepared from fluorinated polymers have widespread and important applications, ranging from protective films for corrosion resistance to high-tech microelectronics and medical devices due to their transparency, low refractive index, stain resistance, and antifouling properties. However, the application of existing coatings is hindered by low surface adhesion to the target substrate and weakness when exposed to mechanical stress or damage, resulting in significant limitations to their practical applications. Herein, we incorporate perfluoropolyether (PFPE) with benzophenone (BP) to develop an efficient coating material (PFPE-BP) possessing broadband anti-reflectivity, anti-contamination properties, excellent abrasion resistance, and stability under elevated temperatures and relative humidity. The presence of BP allows the coating materials to be homogeneously mixed with a commercial hard coating solution to uniformly coat the target substrate. Furthermore, UV light irradiation on the coating surface results in excellent adhesion between BP groups of PFPE-BP and the hard coating matrix.

Superlubricity between Graphite Layers in Ultrahigh Vacuum

Graphite has been conventionally believed to exhibit an inferior lubricating performance with significantly larger friction coefficient and wear rate in a vacuum environment than in ambient air. Dangling bonds at the edge planes of graphite, accounting for the high friction in inert atmosphere are saturated by chemisorbed vapor molecules in air, which contributes to low surface adhesion and low friction. However, there is still a lack of direct experimental evidence whether basal planes of graphite excluding the negative effects of edges or dangling bonds shows intrinsic lubricity when sliding under ultrahigh vacuum (UHV) conditions. By the interlayer friction measurement enabled by graphite flake-wrapped atomic force microscope tips in UHV, we show a record-low friction coefficient of 4 × 10-5 (slope of friction vs normal force curve) when sliding between graphite layers, which is much lower than that in ambient air. This discrepancy manifests the intrinsic sliding frictional behavior between the graphite basal planes when the tribo-materials and experimental conditions are well-designed and strictly controlled. In addition, the temperature dependence of the kinetic friction between the graphite layers has been investigated under UHV conditions over the temperature range of 125-448 K, which is consistent with the thermally activated process.