Air Plasma Etching Research Articles

Fluorine-free, superhydrophobic self-healing and UV-blocking cotton fabric for oil/water separation.

The discharge of oily wastewater not only pollutes waters but also deteriorates our living environment. Superhydrophobic cotton fabric is considered as an important remedy material for oily wastewater cleanup due to outstanding advantages including low cost, high porosity and switchable wettability. However, the existing superhydrophobic fabrics cannot exhibit durable superhydrophobicity during real-life applications due to poor interaction between the coatings and fabric substrates. To address this issue, one-step strategy is proposed to fabricate superhydrophobic cotton fabric by immersion in a octa-[2-(carboxyl methyl thio) ethyl]-polyhedral oligomeric silsesquioxane/cerium dioxide/polydimethylsiloxane (POSS/CeO2/PDMS) coating. As expected, the finished cotton fabric exhibits robust superhydrophobic resistance to mechanical abrasion and chemical corrosions. Notably, the finished cotton fabric shows thermal self-healing superhydrophobicity even if undergone repetitive abrasion cycles and air plasma etching. It is proposed that the rising temperature accelerates the rotations of PDMS chains and the migrations of MAPOSS and CeO2, contributing superhydrophobic self-healing of the damaged cotton fabric. Meanwhile, the superhydrophobic fabric displays high oil/water separation efficiency even in strong acid and alkali environments. Additionally, the POSS/CeO2/PDMS coating improves mechanical, thermal and UV-blocking properties of the finished cotton fabric. This work will pave a way to exploitation and applications of novel multifunctional textiles.

All-weather self-healing superhydrophobic coating functionalized with the cauliflower-like PPy and TiN on cotton fabric for efficient oil-water separation

Superhydrophobic materials are currently undergoing rapid development in various industries, with increasing attention being paid to their service life. Herein, we report an all-weather self-healing superhydrophobic cotton fabric based on photothermal and Joule-heating effects, which can be used for efficient oil-water separation. With the assistance of Safranine T, unique cauliflower-like polypyrrole (PPy) was prepared. Subsequently, titanium nitride (TiN) was loaded to enhance the photothermal performance of the fabric, and polydimethylsiloxane (PDMS) was grafted onto surface to improve the water repellency of PPy@TiN/PDMS fabric. The fabric not only has strong light absorption in visible-near infrared region, but also has good Joule-heating effect, up to 116.3 °C (light intensity of 5 sun) and 128.5 °C (voltage of 8 V). Due to unique all-weather heating performance, the migration of low surface energy PDMS chains is accelerated, so that the PPy@TiN/PDMS fabric after air plasma etching and oxydation can quickly heal its water contact angle (WCA) to 156° under light or low voltage conditions. Additionally, the fabric demonstrates an outstanding performance for the separation of various oil-water mixtures and in multiple cycle separation experiments. This study presents a novel approach for extending the longevity of superhydrophobicity and addressing the issue of waste oil treatment.

Selective Cu electroplating enabled by surface patterning and enhanced conductivity of carbon fiber reinforced polymers upon air plasma etching

We demonstrate a sustainable post-processing of carbon fiber reinforced epoxy polymer (CFRP) composites by air plasma etching that permits regular electroconductive surface patterning through direct Cu galvanic metallization, in contrast to the untreated composite. Our study reveals a significant property dependence of the composite with respect to the position to the fiber/matrix composite surface and treatment. The enhancement in electrical conductivity was not compromised by the lower structural integrity of the composite, as the embedded carbon fibers remained unaffected by the air plasma etching process. The metallized Cu domains on the composite exhibit good hardness and excellent solderability potential. Thus, the electroconductive surface patterning of the composite, preceding galvanic metallization, facilitates the selective deposition of Cu layer domains. This step by step process, relying on the creation of selective electroconductive areas on the composite by plasma etching, enables galvanic metallization. Consequently, it enhances the potential for multifunctional composite applications. The feasibility of galvanic metallization brings new perspectives in selective metallization of composites by allowing the tailoring of the metal layer thickness, microstructure and selection of the metal.

A facile nanopattern modification of silk fibroin electrospun scaffold and the corresponding impact on cell proliferation and osteogenesis.

As a well-known natural protein biomaterial, silk fibroin (SF) has shown broad application prospects in typical biomedical fields. However, the mostly used SF from Bombyx mori silkworm lacks specific cell adhesion sites and other bioactive peptide sequences, and there is still significant room for further improvement of their biological functions. Therefore, it is crucial to develop a facile and effective modification strategy for this widely researched biomaterial. In this study, the SF electrospun scaffold has been chosen as a typical SF biomaterial, and air plasma etching has been adopted as a facile nanopattern modification strategy to promote its biological functions. Results demonstrated that the plasma etching could feasibly and effectively create nano-island-like patterns on the complex surface of SF scaffolds, and the detailed nanopattern features could be easily regulated by adjusting the etching time. In addition, the mesenchymal stem cell responses have illustrated that the nanopattern modification could significantly regulate corresponding cell behaviors. Compared with the non-etched scaffold, the 10 min-etched scaffolds (10E scaffold) significantly promoted stem cell proliferation and osteogenic differentiation. Moreover, 10E scaffold has also been confirmed to effectively accelerate vascularization and ectopic osteogenesis in vivo using a rat subcutaneous implantation model. However, the mentioned promoting effects would be weakened or even counteracted with the increase of etching time. In conclusion, this facile modification strategy demonstrated great application potential for promoting cell proliferation and differentiation. Thus, it provided useful guidance to develop excellent SF-based scaffolds suitable for bone and other tissue engineering.

Controllable hydrophilic/superhydrophobic patterned coatings for optical information encryption/decryption based on water-triggered opaque to translucent transition

Anti-counterfeiting technologies are crucial for securing the authenticity and proof of commodities, in which the optical information encryption/decryption has attracted extensive attention for its overriding advantages of visibility and convenience. Inspired by the unique transparency transformation phenomenon of Diphylleia grayi petals, a controllable hydrophilic/superhydrophobic patterned coating with water-triggered opaque to translucent transition is proposed through the construction of a superhydrophobic coating, subsequent air plasma etching under a mask, and final hydrophilic modification to introduce stable invisible patterns. The superhydrophobic region exhibits great water repellency with a water contact angle (WCA) at 157°, while the hydrophilic region quickly absorbs water with a WCA at 61°. The patterned coating presents an opaque state for the serious light scattering induced by the rough microstructure and large refractive index difference between the coating and air, while the hydrophilic patterns on the coating transform to translucent after water infiltration for the reduced roughness and close refractive indexes of the coating and water. The information revealing is rapid and reversible, and demonstrates heat and long-term stability and great reusability. The findings conceivably stand out as a new methodology to fabricate controllable superwettable coatings with optical information encryption/decryption capability for application in anti-counterfeiting.

Electron transfer characteristics of amino acid adsorption on epitaxial graphene FETs on SiC substrates

Clarifying the adsorption characteristics of biomolecules on graphene surfaces is critical for the development of field-effect transistor (FET)-based biosensors for detecting pH, DNA, proteins, and other biomarkers. Although there are many reports on biomolecule detection using graphene FETs, the detection mechanism has not yet been clarified. In this study, the adsorption behavior and electron transfer characteristics of 20 proteinogenic amino acids on graphene field-effect transistors are investigated. Large single-crystal graphene films were epitaxially grown on SiC substrates by a resist-free metal stencil mask lithography process then patterned by air plasma etching to form FET devices. Amino acids with different charge conditions (positive or negative charge) were introduced onto the epitaxial graphene surface in solution. The charge neutral points of the drain current vs gate voltage curves shifted in the negative gate voltage direction after the introduction of all amino acids, regardless of the type of amino acid and its charge condition. These amino acid adsorption characteristics agree well with previously reported protein adsorption characteristics on epitaxial graphene surfaces, indicating that the adsorption of proteins in the liquid phase occurs by electron doping to the graphene surface. These results indicate that non-specific protein binding always leads to electron doping of epitaxial graphene FETs.

Facile fabrication of wafer-scale flexible SERS substrate via cryo-transferring SiO2 nanosphere multilayer into waterborne polyurethane (WPU) film

Preparing flexible Surface-Enhanced Raman Scattering (SERS) substrates with close-packed nanosphere monolayer has attracted considerable interest. Regrettably, although nanosphere (NS) multilayer can be much more easily assembled at a large area than monolayer, it has not yet been employed in the SERS field. Herein, we report the facile fabrication of wafer-scale flexible SERS substrate with NS multilayer for the first time. In detail, we cryo-transferred SiO2 NS multilayer which was easily spin-coated on host Si substrate completely into waterborne polyurethane (WPU) film, followed by air plasma etching to remove part of WPU to make only one layer of embedded SiO2 NS exposed. Cauliflower-like Au nanostructure with abundant “hot spots” was formed on NS crowns by e-beam evaporation, finally enabling the 2-inch flexible SERS substrate with a rhodamine 6G (R6G) detection limit of 10-9 M and the corresponding enhancement factor (EF) of ∼108.

Enhanced Conductivity of Reinforced Carbon Fibers Induced by Air Plasma Etching of Composites

Enhanced Conductivity of Reinforced Carbon Fibers Induced by Air Plasma Etching of Composites

Modulating Optical Characteristics of Nanoimprinted Plasmonic Device by Re-Shaping Process of Polymer Mold.

Metal nanostructures exhibit specific optical characteristics owing to their localized surface plasmon resonance (LSPR) and have been studied for applications in various optical devices. The LSPR property strongly depends on the size and shape of metal nanostructures; thus, plasmonic devices must be designed and fabricated according to their uses. Nanoimprint lithography (NIL) is an effective process for repeatedly fabricating metal nanostructures with controlled sizes and shapes and require optical properties. NIL is a powerful method for mass-producible, low-cost, and large-area fabrication. However, the process lacks flexibility in adjusting the size and shape according to the desirable optical characteristics because the size and shape of metal nanostructures are determined by a single corresponding mold. Here, we conducted a re-shaping process through the air-plasma etching of a polymer’s secondary mold (two-dimensional nanopillar array made of cyclo-olefin polymer (COP)) to modulate the sizes and shapes of nanopillars; then, we controlled the spectral characteristics of the imprinted plasmonic devices. The relationship between the structural change of the mold, which was based on etching time, and the optical characteristics of the corresponding plasmonic device was evaluated through experiments and simulations. According to evaluation results, the diameter of the nanopillar was controlled from 248 to 139 nm due to the etching time and formation of a pit structure. Consequently, the spectral properties changed, and responsivity to the surrounding dielectric environment was improved. Therefore, plasmonic devices based on the re-shaped COP mold exhibited a high responsivity to a refractive index of 906 nm/RIU at a wavelength of 625 nm.

Tensegrity Modelling and the High Toughness of Spider Dragline Silk.

This work establishes a tensegrity model of spider dragline silk. Tensegrity systems are ubiquitous in nature, being able to capture the mechanics of biological shapes through simple and effective modes of deformation via extension and contraction. Guided by quantitative microstructural characterization via air plasma etching and low voltage scanning electron microscopy, we report that this model is able to capture experimentally observed phenomena such as the Poisson effect, tensile stress-strain response, and fibre toughness. This is achieved by accounting for spider silks’ hierarchical organization into microfibrils with radially variable properties. Each fibril is described as a chain of polypeptide tensegrity units formed by crystalline granules operating under compression, which are connected to each other by amorphous links acting under tension. Our results demonstrate, for the first time, that a radial variability in the ductility of tensegrity chains is responsible for high fibre toughness, a defining and desirable feature of spider silk. Based on this model, a discussion about the use of graded tensegrity structures for the optimal design of next-generation biomimetic fibres is presented.

Plasma-etched electrospun nanofiber membrane as adsorbent for dye removal

The removal of hazardous dyes from wastewater is essential for environmental remediation. A simple, green and effective air plasma etching treatment was introduced to fabricate PLLA nanofibrous adsorbents. The cationic methylene blue (MB) dye could be rapidly adsorbed on the surface of plasma-etched PLLA nanofiber membrane through electrostatic interaction. It was attributed to the increased surface area and the generated binding sites after the plasma treatment. The adsorption behavior was influenced by both the plasma etching time and the initial MB concentration. It was found that the adsorption kinetics fits well with the pseudo-second order model, and the isotherm data fits well with the Langmuir model, revealing that monolayer MB was chemically adsorbed on the adsorbent. Moreover, the plasma-etched PLLA nanofiber membrane has also exhibited good reusability. It is believed that the plasma treatment may facilitate the design and fabrication of a new class of nanofibrous adsorbents.

Feasibility of Plasma Treated Clay in Clay/Polymer Nanocomposites Powders for use Laser Sintering (LS)

The addition of small quantities of nano-clay to nylon is known to improve mechanical properties of the resulting nano-composite. However, achieving a uniform dispersion and distribution of the clay within the base polymer can prove difficult. A demonstration of the fabrication and characterization of plasma-treated organoclay/Nylon12 nanocomposite was carried out with the aim of achieving better dispersion of clay platelets on the Nylon12 particle surface. Air-plasma etching was used to enhance the compatibility between clays and polymers to ensure a uniform clay dispersion in composite powders. Downward heat sintering (DHS) in a hot press is used to process neat and composite powders into tensile and XRD specimens. Morphological studies using Low Voltage Scanning Electron Microscopy (LV-SEM) were undertaken to characterize the fracture surfaces and clay dispersion in powders and final composite specimens. Thermogravimetric analysis (TGA) testing performed that the etched clay (EC) is more stable than the nonetched clay (NEC), even at higher temperatures. The influence of the clay ratio and the clay plasma treatment process on the mechanical properties of the nanocomposites was studied by tensile testing. The composite fabricated from (3% EC/N12) powder showed ~19 % improvement in elastic modulus while the composite made from (3% NEC/N12) powder was improved by only 14%). Most notably however is that the variation between tests is strongly reduced when etch clay is used in the composite. We attribute this to a more uniform distribution and better dispersion of the plasma treated clay within polymer powders and ultimately the composite.

Development of Polysulfone Hollow Fiber Porous Supports for High Flux Composite Membranes: Air Plasma and Piranha Etching

For the development of high efficiency porous supports for composite membrane preparation, polysulfone (PSf) hollow fiber membranes (outer diameter 1.57 mm, inner diameter 1.12 mm) were modified by air plasma using the low temperature plasma treatment pilot plant which is easily scalable to industrial level and the Piranha etch (H2O2 + H2SO4). Chemical and plasma modification affected only surface layers and did not cause PSf chemical structure change. The modifications led to surface roughness decrease, which is of great importance for further thin film composite (TFC) membranes fabrication by dense selective layer coating, and also reduced water and ethylene glycol contact angle values for modified hollow fibers surface. Furthermore, the membranes surface energy increased two-fold. The Piranha mixture chemical modification did not change the membranes average pore size and gas permeance values, while air plasma treatment increased pore size 1.5-fold and also 2 order enhanced membranes surface porosity. Since membranes surface porosity increased due to air plasma treatment the modified membranes were used as efficient supports for preparation of high permeance TFC membranes by using poly[1-(trimethylsilyl)-1-propyne] as an example for selective layer fabrication.

Air plasma etching towards rich active sites in Fe/N-porous carbon for the oxygen reduction reaction with superior catalytic performance

Plasma etching removed less stable carbons and exposed the active sites in Fe–N/C catalysts which resulted in excellent performances towards the oxygen reduction reaction in both acidic and alkaline media.

Superhydrophobic Surface by Replication of Laser Micromachined Pattern in Epoxy/Alumina Nanoparticle Composite

Superhydrophobic surfaces were obtained by superposition of microstructure—defined by replication of laser micromachined masters, with nanostructure—created by durable epoxy/γ‐Al2O3 nanoparticle composite, used for replication. Hierarchical surface topography thus obtained consisted of hexagonally spaced microcavities and nanoparticle agglomerates, exposed on the replica surface by radio frequency (RF) air plasma etching. Surface topography was further enhanced by rims around the microcavity edges, resulting from nanosecond laser micromachining defects in aluminum masters. Subsequent wet chemical hydrophobization with 1H,1H,2H,2H‐perfluorotetradecyltriethoxysilane (PFTDTES) provided superhydrophobic behavior in replicas with a microcavity spacing of 30 μm, as indicated by a water contact angle of 160° and a sliding angle of 8°. The preparation method is relatively simple, inexpensive, and potentially scalable.

Superhydrophobic dual-sized filler epoxy composite coatings

We propose an accessible method of superhydrophobic coating fabrication, in the form of an epoxy resin composite with hard nano- and microfillers, combined with surface sandblasting and wet chemical hydrophobization. The fillers – glass microbeads and Al2O3 nanoparticles, dispersed in the bulk composite – provide a dual-sized roughness, if exposed on the surface. Sandblasting with corundum particles and subsequent air plasma etching exposes and enhances the micro- and nano-scale roughness, while wet chemical modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane reduces surface free energy to the level required for superhydrophobic materials. The coatings exhibit superhydrophobic behavior, with water contact angle of 152° and contact angle hysteresis of 8°. Hierarchical surface structure of coatings is preserved after erosive wear tests and superhydrophobicity is restored upon re-hydrophobization.

Surface modification of chromatography adsorbents by low temperature low pressure plasma

In this study we show how low temperature glow discharge plasma can be used to prepare bi-layered chromatography adsorbents with non-adsorptive exteriors. The commercial strong anion exchange expanded bed chromatography matrix, Q HyperZ, was treated with plasmas in one of two general ways. Using a purpose-designed rotating reactor, plasmas were employed to either: (i) remove anion exchange ligands at or close to the exterior surface of Q HyperZ, and replace them with polar oxygen containing functions (‘plasma etching and oxidation’); or (ii) bury the same surface exposed ligands beneath thin polymer coatings (‘plasma polymerization coating’) using appropriate monomers (vinyl acetate, vinyl pyrrolidone, safrole) and argon as the carrier gas. X-ray photoelectron spectroscopy analysis (first ∼10 nm depth) of Q HyperZ before and after the various plasma treatments confirmed that substantial changes to the elemental composition of Q HyperZ's exterior had been inflicted in all cases. The atomic percent changes in carbon, nitrogen, oxygen, yttrium and zirconium observed after being exposed to air plasma etching were entirely consistent with: the removal of pendant Q (trimethylammonium) functions; increased exposure of the underlying yttrium-stabilised zirconia shell; and introduction of hydroxyl and carbonyl functions. Following plasma polymerization treatments (with all three monomers tested), the increased atomic percent levels of carbon and parallel drops in nitrogen, yttrium and zirconium provided clear evidence that thin polymer coats had been created at the exteriors of Q HyperZ adsorbent particles. No changes in adsorbent size and surface morphology, nor any evidence of plasma-induced damage could be discerned from scanning electron micrographs, light micrographs and measurements of particle size distributions following 3 h exposure to air (220 V; 35.8 W L −1) or ‘vinyl acetate/argon’ (170 V; 16.5 W L −1) plasmas. Losses in bulk chloride exchange capacity before and after exposure to plasmas enabled effective modification depths within hydrated Q HyperZ adsorbent particles to be calculated as 0.2–1.2 μm, depending on the conditions applied. The depth of plasma induced alteration was strongly influenced by the power input and size of the treated batch, i.e. dropping the power or increasing the batch size resulted in reduced plasma penetration and therefore shallower modification. The selectivity of ‘surface vs. core’ modification imparted to Q HyperZ by the various plasma treatments was evaluated in static and dynamic binding studies employing appropriate probes, i.e. plasmid DNA, sonicated calf thymus DNA and bovine serum albumin. In static binding studies performed with adsorbents that had been exposed to plasmas at the 5 g scale (25 g L −1 of plasma reactor), the highest ‘surface/core’ modification selectivity was observed for Q HyperZ that had been subjected to 3 h of air plasma etching at 220 V (35.8 W L −1). This treatment removed ∼53% of ‘surface’ DNA binding at the expense of a 9.3% loss in ‘core’ protein binding. Even more impressive results were obtained in dynamic expanded bed adsorption studies conducted with Q HyperZ adsorbents that had been treated with air (220 V, 3 h) and ‘vinyl acetate/argon’ (170 V, 3 h) plasmas at 10.5 g scale (52.5 g L −1 of plasma reactor). Following both plasma treatments: the 10% breakthrough capacities of the modified Q HyperZ adsorbents towards ‘surface’ binding DNA probes dropped very significantly (30–85%); the DNA induced inter-particle cross-linking and contraction of expanded beds observed during application of sonicated DNA on native Q HyperZ was completely eradicated; but the ‘core’ protein binding performance remained unchanged cf. that of the native Q HyperZ starting material.

Loading effect at air plasma etching of fabric of polyethylene terephthalate fibers

The results of studying the loading effect at low temperature air plasma action on the surface of fabric of polyethylene terephthalate filament yarns are presented. Gravimetric and mass-spectrum techniques were used in this work. Gas evolution changes plasma properties and, as a consequence, the target process kinetics. Due to the mutual influence of heterogeneous and volumetric processes not only flows of active oxygen particles on the material surface reduce but also the correlations of these flows change. The NO molecule concentration is closely connected with the atom oxygen balance. Even when the fraction of the reactor surface occupied by the fabric is relatively low, the NO molecules’ concentration drops appreciably. For a wide interval of discharge parameters, the specific rates of etching, the oxygen absorption from the gas phase, the gaseous product formation, and the NO molecule concentration decrease extensively when the reactor load ratio is increased from 6% to 50%. The interconnected influence of the parameters and the loading is shown in the behavior of the reaction product formation. In the case of the load ratio rising, the correlation of the degradation channels changes to a channel with a yield of CO and H2 stronger at higher initial gas pressure.

A method of visualization of inorganic nanoparticles dispersion in nanocomposites

Air plasma etching followed by scanning electron microscope (SEM) imaging technique for visualizing the inorganic nanofillers in polymeric composites is a promising technique for quick screening of exfoliation and dispersion of nanofillers in nanocomposites in manufacturing and materials development environments. The method was applied to three different nanocomposites, namely, montmorillonite (MMT) clay vinyl ester, carbon nanotube (CNT) vinyl ester and MMT epoxy nanocomposites samples produced using high shear mixing. Results were compared with transmission electron microscope data. The etch rate for 2%MMT/vinyl ester and 1%MMT/epoxy nanocomposites varied from 1 to 2 nm/min.

A method of visualization of dispersion of nanoplatelets in nanocomposites

Air plasma etching followed by scanning electron microscope imaging technique for visualizing the inorganic nanofillers in polymeric composites is a promising technique for quick screening of exfoliation and dispersion of nanofillers in nanocomposites in manufacturing and materials development environments. The method was applied to study montmorillonite (MMT) clay with vinyl ester nanocomposite samples produced using high shear mixing. Results were compared with transmission electron microscope data. The study details the versatility and the use of this technique for visualization of inorganic platelets. The etch rate for MMT/vinyl ester and neat resin initially was 3 and 4 nm/min and increased to about 8 and 10 nm/min, respectively.