Fluorinated Diamond-like Carbon Research Articles

Ultra-resilient multi-layer fluorinated diamond like carbon hydrophobic surfaces

Seventy percent of global electricity is generated by steam-cycle power plants. A hydrophobic condenser surface within these plants could boost overall cycle efficiency by 2%. In 2022, this enhancement equates to an additional electrical power generation of 1000 TWh annually, or 83% of the global solar electricity production. Furthermore, this efficiency increase reduces CO2 emissions by 460 million tons /year with a decreased use of 2 trillion gallons of cooling water per year. However, the main challenge with hydrophobic surfaces is their poor durability. Here, we show that solid microscale-thick fluorinated diamond-like carbon (F-DLC) possesses mechanical and thermal properties that ensure durability in moist, abrasive, and thermally harsh conditions. The F-DLC coating achieves this without relying on atmospheric interactions, infused lubricants, self-healing strategies, or sacrificial surface designs. Through tailored substrate adhesion and multilayer deposition, we develop a pinhole-free F-DLC coating with low surface energy and comparable Young’s modulus to metals. In a three-year steam condensation experiment, the F-DLC coating maintains hydrophobicity, resulting in sustained and improved dropwise condensation on multiple metallic substrates. Our findings provide a promising solution to hydrophobic material fragility and can enhance the sustainability of renewable and non-renewable energy sources.

Antibacterial Fluorinated Diamond-like Carbon Coating Promotes Osteogenesis—Comparison with Titanium Alloy

Fluorinated diamond-like carbon (F-DLC) coating is biologically safe, provides superior antibacterial properties, and shows promise in preventing postoperative peri-implant infections. However, potential negative effects of this coating on in vivo bone formation and resorption have not been studied. The authors investigated the effects of F-DLC coatings on bone union in beagle dogs. Seventy-two solid columns of titanium alloy were prepared with equally spaced slits. Half of these columns were coated with F-DLC (Group F), and the others were left uncoated as controls (Group C). Columns were implanted in the femurs of beagle dogs, and in vivo bone formation and resorption were assessed 4, 8, and 12 weeks after implantation. In comparison to Group C, Group F showed significantly greater bone volume and trabecular thickness at Week 8 (p < 0.05) and Week 12 (p < 0.005) and significantly lower bone resorption activity, measured by the ratio of osteoclasts to bone surface and of eroded surface to bone surface, at Week 12 (p < 0.05). The F-DLC coating encouraged bone formation in vivo more effectively than uncoated titanium alloy, suggesting that F-DLC will prove to be a useful coating material for antibacterial intraosseous implants.

Formation of Tribofilm in the Friction of Fluorinated Diamond-Like Carbon (FDLC) Film against Ti6Al4V in Bovine Serum Albumin (BSA) Solution

A route to reducing the wear of the metal counterpart in the friction of meatal against diamond-like carbon (DLC) is to form a lubricating tribofilm on the metal counterface. However, in liquid lubricating conditions, the formation of tribofilm can be influenced by both the lubricating medium and the counterpart material. Here we report the effect of lubricating biomolecule and doping fluorine element on the formation of tribofilm in fluorinated DLC (FDLC)-Ti6Al4V friction system. A group of ball-on-disc frictional experiments with different sliding speeds and normal loads were performed in phosphate buffer solution (PBS) and bovine serum albumin (BSA) solution. The results showed the formation of tribofilm was inhibited by the absorption of biomolecules on the frictional surface, thus improving the friction coefficient and wear of Ti6Al4V counterpart. Doping fluorine into DLC film also can restrain the formation of tribofilm on Ti6Al4V counterface. As a result, tribofilm is difficult to form when Ti6Al4V counterface slides against FDLC in BSA solution. Fluorinated DLC film should be considered carefully for the anti-wear use in body fluid containing biomolecules because it might cause severe wear of the counterpart material.

Effect of Fluorine Incorporation on DLC Films Deposited by Pulsed Cathodic Arc Deposition on Nitrile Butadiene Rubber and Polyurethane Rubber Substrates

Diamond-like carbon (DLC) and fluorinated diamond-like carbon (F-DLC) films were deposited via pulsed cathodic arc deposition on pretreated nitrile butadiene rubber (NBR) and polyurethane (PU) rubber substrates. Both DLC and F-DLC films showed a more than 50% decrease in coefficients of friction compared to uncoated NBR and PU rubber substrates. The incorporation of fluorine was found to have little influence on the film coefficient of friction. However, a decrease in film wettability was overserved in the F-DLC films compared to the DLC films.

Synthesis of Thermoplastic Poly(2-methoxyethyl acrylate)-Based Polyurethane by RAFT and Condensation Polymerization.

Thermoplastic solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) is synthesized through the reversible addition-fragmentation chain transfer (RAFT) polymerization and the condensation polymerization, using hydroxyl-terminated RAFT reagents and diisocyanate, respectively. Neat PMEA is a promising antithrombogenic liquid used in the medical fields. The thermoplastic property of the solid PMEA-based PU due to hydrogen bonding is confirmed by the dynamic mechanical analysis (DMA) at temperature below 72 °C. The antithrombogenic property of PMEA-based PU is also analyzed by the platelet adhesion test. The number of platelets on PMEA-based PU is 17 cells per unit area, which is smaller than that on the fluorinated diamond-like carbon (F-DLC), a well-known highly antithrombogenic material. It is concluded that a newly synthesized PMEA-based PU exhibits thermoplastic characteristics with excellent antithrombogenicity.

Evaluation of Antibacterial and Cytotoxic Properties of a Fluorinated Diamond-Like Carbon Coating for the Development of Antibacterial Medical Implants.

Peri-implant infection is a serious complication in surgical procedures involving implants. We conducted an in vitro study to determine whether the use of a fluorinated diamond-like carbon (F-DLC) coating on a titanium alloy surface can prevent peri-implant infection. After applying the F-DLC, we evaluated its antibacterial and cytotoxic properties. The coating groups, containing controlled fluorine concentrations of 5.44%, 17.43%, 24.09%, and 30%, were examined for the presence of Staphylococcus aureus and Escherichia coli according to ISO 22196 for the measurement of antibacterial activity on plastics and other nonporous surfaces. Biological toxicity was evaluated using Chinese hamster V79 cells according to ISO 10993-5 for the biological evaluation of medical devices. In the control group, populations of S. aureus and E. coli substantially increased from 2.4 × 104 to (1.45 ± 1.11) × 106 colony-forming units (CFUs) and from 2.54 × 104 to (4.04 ± 0.44) × 106 CFUs, respectively. However, no bacteria colonies were detected in any F-DLC group with a fluorine concentration of ≥ 17.43%. In the biological toxicity study, an F-DLC coating with a fluorine concentration of 30% showed a colony formation rate of 105.8 ± 24.1%, which did not differ significantly from the colony formation rate of 107.5 ± 31.1% in the nontoxic control group. An F-DLC coating on titanium alloy discs showed excellent in vitro antibacterial activity with no biological toxicity.

Time-Dependent Wetting Scenarios of a Water Droplet on Surface-Energy-Controlled Microcavity Structures with Functional Nanocoatings.

We report the surface-energy-dependent wetting transition characteristics of an evaporating water droplet on surface-energy-controlled microcavity structures with functional nanocoatings. The droplet wetting scenarios were categorized into four types depending on the synergistic effect of surface energy and pattern size. The silicon (Si) microcavity surfaces (γSi = 69.8 mJ/m2) and the polytetrafluoroethylene (PTFE)-coated microcavity surfaces (γPTFE = 15.0 mJ/m2) displayed stable Wenzel and Cassie wetting states, respectively, irrespective of time. In contrast, diamond-like carbon (DLC)-coated (γDLC = 55.5 mJ/m2) and fluorinated diamond-like carbon (FDLC)-coated (γFDLC = 36.2 mJ/m2) surfaces demonstrated a time-dependent transition of wetting states. In particular, the DLC-coated surface showed random filling of microcavities at the earlier time point, while the FDLC-coated surface displayed directional filling of microcavities at the late stage of drop evaporation. Such dynamic wetting scenarios based on surface energy, in particular, the random and directional wetting transitions related to surface energy of nanocoatings have not been explored previously. Furthermore, the microscopic role of nanocoating in the wetting scenarios was analyzed by monitoring the time-dependent deformation and movement of the air-water interface (AWI) at individual cavities using the fluorescence interference-contrast (FLIC) technique. A coating-dependent depinning mechanism of the AWI was responsible for variable filling of cavities leading to time-dependent wetting scenarios. A capillary wetting model was used to relate this depinning event to the evaporation-induced internal flow within the droplet. Interestingly, FLIC analysis revealed that a hydrophilic nanocoating can induce microscopic hydrophobicity near the cavity edges leading to delayed and variable cavity filling. The surface energy-dependent classification of the wetting scenarios may help the design of novel evaporation-assisted thermodynamic and mass-transfer processes.

Development of Highly Durable Sliding Triboelectric Nanogenerator Using Diamond-Like Carbon Films

Climate change is affecting every being on the planet. The time has arrived to give a big push for harvesting renewable energy sources, thus reducing the dependencies on fossil fuels and chemical batteries. This inspired Nanotechnologists to explore energy harvesting techniques from the environment. Triboelectric nanogenerator (TENG) is one such emerging, promising, and a reliable technology to extract micropower from the abundantly available natural mechanical energy. In this study, we have addressed the durability issues of TENG using Diamond-like Carbon (DLC) films as a triboelectric surface. Our findings indicate a high potential for DLC films for TENG applications attributing to its outstanding tribological, mechanical and insulating properties. Hydrogenated DLC (H-DLC) film, Fluorinated DLC (F-DLC) film, and PTFE were used as dielectric surfaces on a rotary based sliding-TENG. The output performance of each pair differed with the sliding frequency where H-DLC/F-DLC pair produced the maximum output at a moderate frequency of 4 Hz. As the frequency was raised, H-DLC/PTFE pair exhibited the highest output at 10 Hz, equal to that of the Al/PTFE pair. The durability evaluation of DLC-TENG showed very promising outcomes producing stable output current for 2 h. This study is expected to encourage the development of DLC-based sliding-TENGs, with enhanced durability and output efficiency.

Hydrogen-free fluorinated DLC films with high hardness prepared by using T-shape filtered arc deposition system

Fluorinated diamond-like carbon (F-DLC) films have good surface properties. DLC films with high mechanical hardness are prepared using filtered arc deposition, which is a physical vapor deposition method. In this work, the fabrication of F-DLC films using filtered cathodic arc deposition while introducing a fluorocarbon gas was carried out, and the characteristics of the F-DLC films were investigated. The F-DLC films were deposited on Si and WC substrates using the T-shape filtered arc deposition (T-FAD) system while introducing fluorocarbon gases. The fluorocarbon gases used for this purpose were C3F8, C6F14, or C7F14. The F-DLC characteristics such as surface appearance, film structure, film density, nanoindentation hardness, substrate adhesion, and water contact angle were investigated. The characteristics of the fabricated DLC films were as follows: the fluorine content ranged from 0 to 22 at.%, film density ranged from 2.1 to 3.1 g/cm3, nanoindentation hardness ranged from 10 to 48 GPa, elastic modulus ranged from 140 to 360 GPa, and water contact angle ranged from 66 to 95°. In addition, the F-DLC films showed good adhesion strength on WC substrates. F-DLC films with high mechanical hardness and water repellency were obtained using T-FAD.

Erosion of fluorinated diamond-like carbon films by exposure to soft X-rays

The effects of soft X-ray irradiation on fluorinated diamond-like carbon (F-DLC) films were investigated using synchrotron radiation (SR). The Vickers hardness of the F-DLC films substantially increased from an initial value of about 290 to about 800 HV at a dose of 50 mA·h and the remained constant at about 1100 HV at doses of more than 300 mA·h. This dose dependence was consistent with those of the film thickness and elemental composition. The depth profile of the elemental composition inside each F-DLC film obtained by the measurement of the X-ray photoelectron spectrum (XPS) during sputtering showed that the composition ratio of fluorine was approximately constant from the surface to the neighborhood of the substrate. Namely, fluorine atoms were desorbed by SR irradiation from not only the surface but also the substrate neighborhood. Modification by SR irradiation was found to occur in the entire F-DLC film of about 200 nm thickness.

Effect of TiN/C Microstructure Composite Layer on the Adhesion of FDLC Film onto Silicon Substrate

Deposition techniques of direct current and radio-frequency magnetron sputtering were used to separately prepare TiN/C microstructural composite layer and fluorinated diamond-like carbon (FDLC) film on monocrystalline silicon. The aim was to investigate the effects of microstructural composite layers on the adhesion property of FDLC film. The results indicated that the TiN/C microstructural composite layer can distinguish from the substrate and the FDLC film. After adding the composite layers, the film–substrate binding force significantly increased. When the composite film were prepared at a partial pressure of 0.25, the binding force reached 30.5 N, which was greater than the value of 22.6 N for the sample without composite layers. TiN/C in the composite layers intensified the integration with silicon substrate because the C–C bond acted as a bridge linking the FDLC film to the silicon substrate. Furthermore, the bulges on the surface of the composite layers strengthened the physical bonding of the film with silicon substrates.

Soft X-ray irradiation effect on the fluorinated DLC film

The irradiation effect on fluorinated diamond-like carbon (F-DLC) film was investigated by measuring the dose dependence of various film properties using synchrotron radiation (SR) in the soft X-rays in the SR dose region from 0 to 2000mAh. Film flatness was maintained but various film properties and surface properties were found to be changed by the SR irradiation. Wettability of the F-DLC film surface increased dramatically within 20mAh SR exposure, which was ascribed to the decrease in fluorine on the film surface. Film thickness, film density, composition ratio of fluorine atom in film decreased and sp2/(sp2+sp3) ratio of carbon atoms increased within 300mAh SR exposure, which were ascribed to the desorption of species containing fluorine atoms. In addition, dominant desorbed species emitted from F-DLC film were found in the fluorocarbon group, CFx. Changes in film properties and film thickness did not proceed, when fluorine content in the F-DLC film decreased to about 10% after the 300mAh SR exposure.

Antibacterial properties of fluorinated diamond-like carbon films deposited by direct and remote plasma

The antibacterial activity and cell viability of fluorinated diamond-like carbon (F-DLC) films as bio coating were investigated. The F-DLC films were deposited on polycarbonate substrates by the radiofrequency (RF) plasma (direct mode) and microwave (MW) afterglow plasma (remote mode). The influences of RF and MW power on the fibroblast cell proliferation and antibacterial activity against E.coli were studied. Additionally the relevance of F atoms concentration, surface roughness and surface energy with the antibacterial activity was investigated. The fibroblast cell cultivation tests revealed that the F-DLC films have no toxicity for cells. Increasing the RF power increased the F concentration and surface roughness, lowered the surface energy and eradicated 70% of E.coli bacteria. A drop in this growing trend happened in the remote mode. As the MW power increased, the F content and surface roughness decreased, the films became hydrophilic, and only thirty percent of bacteria was killed.

Review of Surface Modification of Nanoporous Polyethersulfone Membrane as a Dialysis Membrane

Nanoporous polyethersulfone (PES) membrane is widely used as a filtration membrane in hemodialysis systems. Unfortunately, it has low blood compatibility, and induces blood clots that adhere to the membrane’s surface during dialysis treatment. This paper reports on a review of surface modification that is used to improve the PES membrane’s blood compatibility. The method consists of applying two coating materials, in the form of parylene and fluorinated diamond-like carbon (F-DLC) films, onto the membrane’s surface. The parylene film is deposited on the diffusion layer of the membrane surface using glycerin liquid, while the FDLC film is specially coated on the supporting layer of the membrane. The unique property of parylene, which has the characteristics of conformal coating, prevents the parylene from being coated on the supporting layer of the membrane. Conversely, F-DLC film, which is hard, fragile and has a less conformal coating than parylene, is only meant to be coated on the supporting layer. Finally, the coated membranes, along with the bare PES membrane, are compared and investigated under a long-term diffusion test to assess their permeability and blood compatibility. The experiment results show that both coating materials have the capacity to improve the membrane’s blood compatibility in different ways.

3P2-I08 長期にわたるマイクロ透析装置の使用評価(ナノ・マイクロ流体システム)

We have ever developed a micro dialyzer consisting of micro channels and nano-porous polyethersulfone (PES) membrane for dialysis membrane. PES membrane is broadly used as a membrane for nanofiltetration such as fractionation, purification, and dialysis. However in the long term, PES membrane is apt to absorb and make the protein layer, which produces the platelet adhesion when its surface is contacted to the blood, then the performance of our device drastically get worse. Therefore in this work, we modified the PES membrane by coating Fluorinated Diamond Like Carbon (F-DLC) film. We investigated anticoagulants of the F-DLC/PES membrane using a microfluidic device and experimentally showed that the amount of cells absorbed to the surface substantially reduced in F-DLC/PES membrane. We also conducted long term use evaluation of F-DLC/PES membrane for 9 days and the performance of normal PES membrane was seemed to drop off while it was steady in F-DLC/PES membrane.

Antithrombogenicity of Fluorinated Diamond-Like Carbon Films Coated Nano Porous Polyethersulfone (PES) Membrane

A nano porous polyethersulfone (PES) membrane is widely used for aspects of nanofiltration, such as purification, fractionation and dialysis. However, the low-blood-compatibility characteristic of PES membrane causes platelets and blood cells to stick to the surface of the membrane and degrades ions diffusion through membrane, which further limits its application for dialysis systems. In this study, we deposited the fluorinated-diamond-like-carbon (F-DLC) onto the finger like structure layer of the PES membrane. By doing this, we have the F-DLC films coating the membrane surface without sacrificing the membrane permeability. In addition, we examined antithrombogenicity of the F-DLC/PES membranes using a microfluidic device, and experimentally found that F-DLC drastically reduced the amount of blood cells attached to the surface. We have also conducted long-term experiments for 24 days and the diffusion characteristics were found to be deteriorated due to fouling without any surface modification. On the other hand, the membranes coated by F-DLC film gave a consistent diffusion coefficient of ions transfer through a membrane porous. Therefore, F-DLC films can be a great candidate to improve the antithrombogenic characteristics of the membrane surfaces in hemodialysis systems.

Effect of Structure, Composition, and Micromorphology on the Hydrophobic Property of F‐DLC Film

Fluorinated diamond‐like carbon (F‐DLC) films were prepared by radio frequency plasma‐enhanced chemical vapor deposition technique with CF4 and CH4 as source gases under different deposition conditions. The chemical bonding structure and composition of the films were detected by Raman, Fourier transform infrared absorption spectrometry (FTIR), and X‐ray photoelectron spectroscopy (XPS) characterization. The micromorphology and surface roughness of the film were observed and analyzed by atomic force microscopy (AFM). The results indicated that all the prepared films presented a diamond‐like carbon structure. The relative content of fluorine in the films increased, containing more CF2 groups. The ratio of hybrid structure sp3/sp2 decreased. The surface roughness of the films increased when the gas flow ratio R (R = CF4/[CH4 + CF4]) or the deposition power increased. The contact angle of water with the surface of the F‐DLC film was measured with a static drop‐contact angle/surface tension measuring instrument. The hydrophobic property of the F‐DLC films was found to be dependent on the sp2 structure, fluorine content, and surface roughness of the films. The contact angle increased when the relative content of fluorine in the films and sp2 content increased, whereas the contact angle first increased and then decreased with the surface roughness.

Single and dual-mode plasma enhanced chemical vapor deposition of fluorinated diamond-like carbon films

Fluorinated diamond-like carbon (F-DLC) films were deposited on glass and polycarbonate (PC) substrates by radio frequency (RF) and radio frequency/microwave (RF & MW) plasma enhanced chemical vapor deposition, which are called single and dual-mode systems, respectively. A mixture of acetylene (C2H2) and carbon tetra fluoride (CF4) was used for the deposition of the films. The effects of RF and MW powers on the fluorine concentration, micro structure, surface morphology, deposition rate, contact angle, surface energy and optical properties of the films as well as the plasma produced chemical species were investigated. The energy dispersive X-ray analysis (EDX) revealed that the fluorine (F) concentration grew from 12.47 to 16.53at.% with increasing RF power from 50 to 200W. However, the atomic F content began to decrease unexpectedly as the MW plasma was added in the dual-mode system. The Raman spectra showed that by increasing RF power, the G peak position shifted toward higher frequencies and the ID/IG ratio increased. The same trend was almost preserved with increasing MW power. The contact angle measurements revealed that the surface of the films became more hydrophobic as the F content increased. The surface energy decreased from 47.2 to 41.8mN/m by increasing the RF power and then started to reach 50.6mN/m with increasing the MW power. The surface roughness of the films was found to increase with growing concentration of fluorine. Also the deposition rate increased with increasing the RF and MW power. The direct band gap of the films reduced with increasing the RF and MW power as the sp2 cluster size increased in the film structure. In addition the optical emission spectroscopy (OES) data showed the correlation between the chemical species produced in the plasma medium and the F content of the films.

Tribology of fluorinated diamond‐like carbon coatings: first principles calculations and sliding experiments

ABSTRACTSliding contact experiments and first principles calculations were conducted to study tribological properties of aluminium and fluorinated diamond‐like carbon (F‐DLC) surfaces. Sliding tests between Al and an F‐DLC coating generated a low coefficient of friction (COF) of 0.09–0.14 and led to the formation of carbonaceous transfer layers containing AlF3 on the Al surfaces as determined by X‐ray photoelectron spectroscopy. An interface model that examined the interactions between Al (111) and F‐terminated diamond (111) surfaces revealed that F atoms would transfer to the Al surface in increasing quantities with an increase in the contact pressure and the F transfer would lead to the formation of a stable AlF3 compound at the Al surface. The generation of repulsive forces between two F‐passivated surfaces as a result of the F transfer to the Al surface was shown to be responsible for the low COF between Al and F‐DLC. Copyright © 2012 John Wiley & Sons, Ltd.

Characterization and haemocompatibility of fluorinated DLC and Si interlayer on Ti6Al4V

Fluorinated diamond-like carbon (F-DLC) films were deposited on Ti6Al4V substrates by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique using a mixture of methane (CH4) and tetrafluoromethane (CF4) gasses. A 100nm Si interlayer was coated in advance by physical vapor deposition (PVD) to improve the adhesion between F-DLC and Ti alloy. A 200nm TiN-coated specimen with the same Ti6Al4V substrate was also built by PVD as a benchmark. The structure and surface properties of F-DLC coatings, prepared with various fluorine flow ratios, were investigated by using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, liquid drop goniometry, and electrochemical corrosion tests. The blood compatibility was evaluated by measuring haemolysis ratio and platelet-covered area in vitro. The films' spectroscopic results show that the CFx group and fluorine atomic concentration increase as CF4 flow ratio is promoted in the mixture. The surface energy is reduced due to the increased fluorine content. The modified surfaces are characterized by higher hydrophobicity, lower thrombogenicity, and better corrosive protection than the virgin and TiN ones.