Argon Plasma Pretreatment Research Articles

Improved coloration of hemp fabrics via low-pressure argon plasma assisted surface modification

Interest in hemp as a viable cellulosic fibre for clothing has increased, driven partly by its economic benefits and the importance of natural renewable materials in emerging circular economies. However, the coloration and chemical finishing of lignocellulosic fibres such as hemp typically require large quantities of water and chemicals. Argon plasma pretreatment provides a way of modulating the physical properties of hemp fibres to improve the coloration process without compromising other bulk properties such as tensile strength. Such plasma treatments may contribute to alleviating the negative environmental impacts associated with liquid pretreatments, heating, or the use of auxiliary chemicals. Dyeing of hemp fibres is particularly challenging due to its crystalline chemical structure. In this study, low-pressure argon plasma-assisted surface modification of woven hemp fabrics up to 600 s at 40 and 80 Hz was explored for enhanced dyeability, resulting in enhanced dye-fibre bonding. Fourier-transform infrared spectroscopy and Raman spectroscopy of argon plasma pretreated hemp fabrics produced no noticeable changes in the functional groups of the fibres, but a physiochemical modification was observed in terms of the density of polar groups. Scanning electron microscopy (SEM) images revealed marked morphological changes including nano-etching of the fibre surface at certain argon plasma process conditions. The pretreatment process increased fibre hydrophilicity, and enhanced reactivity of the surficial –OH groups towards fibre-reactive and vat dyes, resulting in higher colour strength in dyed woven hemp fabrics. Overall, we envisage such plasma pretreatments may impact positively on the material and energy efficiency of the hemp fabric dyeing process.

Implantable Neural Electrodes Fabrication Based on Perfluoroalkoxyalkane Film.

In this paper, the fabrication of perfluoro-alkoxy alkane (PFA) film-based planar neural electrodes was proposed. The fabrication of PFA-based electrodes started with cleaning of PFA film. The argon plasma pretreatment was performed on the PFA film surface and attached to a dummy silicon wafer. Metal layers were deposited and patterned using the standard Micro Electro Mechanical Systems (MEMS) process. Electrode-sites and pads were opened using reactive ion etching (RIE). Lastly, the electrode patterned PFA substrate film was thermally laminated with the other bare PFA film. Electrical-physical evaluation tests were conducted along with in vitro tests, ex vivo tests and soak tests to evaluate the electrode performance and biocompatibility. The electrical and physical performance of PFA-based electrodes had better performances compared to other biocompatible polymer-based electrodes. Also, the biocompatibility and longevity were verified by cytotoxicity test, elution test, and accelerated life test. The PFA film-based planar neural electrode fabrication was established and evaluated. The PFA based electrodes showed excellent benefits such as long-term reliability, low water absorption rate, and flexibility using the neural electrode. For implantable neural electrodes, hermetic sealing is required for in vivo durability. PFA fulfilled a low water absorption rate with relatively low Young's modulus to increase the longevity and biocompatibility of the devices.

Effect of Argon Glow Plasma Pretreatment of Pure Ta on Hf Coating Preparation

In order to enhance the bonding strength between coatings and substrates, argon glow plasma pretreatment with various times was conducted on tantalum substrates, followed by hafnium coating deposition. The coating, consisting of deposition and a diffusion layer with nanocrystalline grains of dimensions ranging from 10 to 20 nm, obtained on the substrate pretreated for 1 h, manifested the optimal structure, with a maximum thickness of approximately 14 μm and the best adhesion performance of approximately 9.5 N. The study found that the pretreatment led to grain refinement at a depth of approximately 150 nm and an increase in the crystal face spacing of substrate and high-energy defects. In addition, the crystal defects and lightly increased surface roughness enhanced the surface energy, while the Ta (200) and Ta (211) crystal faces, which had a lower combination energy and a more stable state with Hf atoms than the Ta (110) crystal face, were considerably increased on pretreated substrates with a decrease in the Ta (110) crystal face. Consequently, coating elements exhibited enhanced diffusion within the substrate, leading to the better formation of a gradient structure, which effectively improved the adhesion of coatings. Further, this study offers an efficacious approach to enhance coating adhesion and provides a deeper understanding of plasma pretreatment.

Effects of argon plasma pretreatment of Si wafers on Si-Si bonding based on Mo/Au interlayers

To improve the bonding quality of Si-Si wafers bonded based on Mo/Au intermediate layers at room temperature, the surfaces of Si wafers were pretreated with argon plasma, and the effect of argon plasma pretreatment on Si-Si wafer bonding was analyzed by combining experimental and theoretical methods. Owing to the plasma treatment of Si wafers, the surface roughness of Si wafers was significantly reduced, and the bonded Si-Si samples had lower interfacial voidage. The average bonding strength of 11.46 MPa for the argon plasma pretreated Si-Si bonded samples is much higher than the bonding strength of 4.23 MPa for the unpretreated Si-Si bonded samples. The analysis of the fractured surface revealed that the fracture of the Si-Si bonded samples without argon plasma treatment occurred mainly at the Mo/Si interface, while the fracture of the plasma-treated Si-Si bonded samples arose mainly within the bulk Si. Molecular dynamics (MD) simulations suggest that strong atomic diffusion takes place at the Mo/Au interface, while Mo atoms hardly diffuse into the bulk Si. These results indicate that argon plasma pretreatment not only cleans and activates the Si wafer surface but also makes the Si wafer surface smooth, which helps to enhance the deposited Mo/Au film quality and the adhesion between the Mo film and the Si wafer.

Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy

Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.

Effect of argon plasma pre-treatment of healing abutments on peri-implant microbiome and soft tissue integration: a proof-of-concept randomized study

PurposeBiofilm-free implant surface is ultimate prerequisite for successful soft and bone tissue integration. Objective of the study was to estimate the effects of argon plasma healing abutment pre-treatment (PT) on peri-implant soft-tissue phenotype (PiSP), inflammation, plaque accumulation and the microbiome (PiM) between non-treated (NPT) and treated (PT) abutments following 3-months healing period. The hypothesis was that cell-conductive and antimicrobial properties of PT would yield optimal conditions for soft tissue integration.Material and MethodsTwo months following second-phase surgery, microbiological and clinical parameters were assessed around thirty-six healing abutments with two types of microtopography, smooth surface (MACHINED) and ultrathin threaded microsurface (ROUGH). A two level randomization schema was used to achieve equal distribution and abutments were randomly divided into rough and machined groups, and then divided into PT and NPT groups. PiM was assessed using next-generation DNA sequencing.ResultsPiM bacterial composition was highly diverse already two months post-implantation, consisting of key-stone pathogens, early and late colonizers, while the mycobiome was less diverse. PT was associated with lower plaque accumulation and inflammation without significant impact on PiSP, while in NPT clinical parameters were increased and associated with periopathogens. NPT mostly harbored late colonizers, while PT exerted higher abundance of early colonizers suggesting less advanced plaque formation. Interaction analysis in PT demonstrated S. mitis co-occurrence with pro-healthy Rothia dentocariosa and co-exclusion with Parvimonas micra, Porphyromonas endodontalis and Prevotella oris. PiSP parameters were generally similar between the groups, but significant association between PiM and keratinized mucosa width was observed in both groups, with remarkably more expressed diversity in NPT compared to PT. PT resulted in significantly lower BOP and PI around rough and machined abutments, respectively, without specific effect on PiM and PiSP.ConclusionsPT contributed to significantly the less advanced biofilm accumulation and inflammation without specific effects on PiSP.

Adhesion and friction performance of DLC/rubber: The influence of plasma pretreatment

Diamond-like carbon (DLC) films are deposited on rubber surfaces to protect the rubber components, and surface pretreatment of the rubber substrates prior to the film deposition can improve the adhesion between the DLC films and the rubber. Thus, the principal purpose of this work concentrates on determining the effects of argon (Ar), oxygen (O2), nitrogen (N2), and hydrogen (H2) plasma pretreatments on the adhesion and friction performance of the DLC films deposited on rubber (DLC/rubber). The results indicated that the Ar plasma pretreatment promoted the formation of a compact layer on the rubber surface. By contrast, massive fillers were exposed on the rubber surface after oxygen or nitrogen plasma pretreatments. Moreover, the typical micrometer-scale patches divided by random cracks were observed on the surface of DLC/rubber, except for the sample pretreated with oxygen plasma. The adhesion of DLC/rubber was found to strengthen with the removal of weak boundary layers and the generation of free radicals on the rubber surface after plasma pretreatment. The tribo-tests revealed that DLC/rubber with O2, N2, and H2 plasma pretreatments cannot achieve optimal friction performance. Significantly, DLC/rubber with Ar plasma pretreatment exhibited a low and stable friction coefficient of 0.19 and superior wear resistance, which was correlated to the high adhesion, good load-bearing of the rubber surface, and the approximate sine function of the surface profile of the DLC film.

Modification of Leather Surface Using Low-Pressure Plasma and Antimicrobial Reagent

Investigations, which are related to plasma efficiency on the treated leather surface, are significant in the development of ecologically and economically friendly processes in obtaining material of desired functional properties. Through the pretreatments using plasma different chemical-physical reactions in the surface layer of treated leather are occurred resulting in improved reactivity. In this paper, modification and functionalization of bovine leather using 1,2,3,4-butantetracarboxylic acid and chitosan were explored. Pretreatments of leather samples were realised using argon and oxygen plasma to assess various influence of chemically reactive oxygen and inert argon gas. Two different bovine leathers -chrome tanned leather and leather tanned with synthetic tanning agent (Cr-free) were chosen for treatments. Analyse of the surface morphology was conducted with SEM microscopy, while the chemical changes using ATR-FTIR spectroscopy. Antimicrobial effectiveness of treated leather was tested with qualitative Agar diffusion plate test against two bacterial Staphylococcus aureus and Klebsiella pneumoniae. Obtained results indicated how applied oxygen and argon plasma pretreatments in optimized process conditions contribute to the improvement of tested functional properties. Achieved surface changes positively affected on leather surface reactivity and antimicrobial effectiveness, particularly Cr-free leather.

Dramatically enhanced mechanical properties of diamond-like carbon films on polymer substrate for flexible display devices via argon plasma pretreatment

Hydrogen-free diamond-like carbon (DLC) films have been deposited on polyimide (PI) substrate at room temperature using the sputtering with a novel nanodiamond target. Also, argon plasma pretreatment procedure for PI substrate was optimized to improve the adhesion and characteristics of the as-prepared DLC film. The deposited DLC film on the PI substrate pretreated with −400 V of bias voltage was found to possess the highest sp3 bonding fraction of 53%, the pencil hardness of 3H, and the optical transmittance of 82%, respectively. The research work demonstrates prosperous applications of DLC films in the protective coating for commercialized optoelectronic devices.

Conversion of Functional Group on PTFE Surface by Argon Plasma Pre-treatment and Polydopamine Coating

The mussel-inspired polydopamine (PDA) coating, which is unstable and fragile on poly(tetrafluoroethylene) (PTFE) surface, is now successfully stabilized by using argon plasma treatment as a pre-treatment before conducting PDA coating. In this study, the parameters of plasma including plasma energies, gas pressures and treating time were adjusted to construct a stable PDA coating layer on PTFE surface. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the surfaces. The sonication stability of PDA coating layer on plasma treated PTFE surface was evaluated. The robust PDA coating layer reported in this study can act as a reactive platform for further modification and reaction on PTFE.

Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors

Further improvements in the low frequency sensitivity of gravitational wave detectors are important for increasing the observable population of astrophysical sources, such as intermediate mass compact black hole binary systems. Improvements in the lower stage mirror and suspension systems will set challenging targets for the required thermal noise performance of the cantilever blade springs, which provide vertical softness and, thus, isolation to the mirror suspension stack. This is required due to the coupling between the vertical and horizontal axes due to the curvature of the Earth. This can be achieved through use of high mechanical Q materials, which are compatible with cryogenic cooling, such as crystalline silicon. However, such materials are brittle, posing further challenges for assembly/jointing and, more generally, for long-term robustness. Here, we report on experimental studies of the breaking strength of silicon at room temperature, via both tensile and 4-point flexural testing; and on the effects of various surface treatments and coatings on durability and strength. Single- and multi-layer DLC (diamond-like carbon) coatings, together with magnetron-sputtered silica and thermally-grown silica, are investigated, as are the effects of substrate preparation and argon plasma pre-treatment. Application of single- or multi-layer DLC coatings can significantly improve the failure stress of silicon flexures, in addition to improved robustness for handling (assessed through abrasion tests). Improvements of up to 80% in tensile strength, a twofold increase in flexural strength, in addition to a 6.4 times reduction in the vertical thermal noise contribution of the suspension stack at 10 Hz are reported (compared to current Advanced LIGO design). The use of silicon blade springs would also significantly reduce potential ‘crackling noise’ associated with the underlying discrete events associated with plastic deformation in loaded flexures.

MicroRNA profile in neosquamous esophageal mucosa following ablation of Barrett's esophagus.

AIMTo investigate the microRNA expression profile in esophageal neosquamous epithelium from patients who had undergone ablation of Barrett’s esophagus.METHODSHigh throughput screening using TaqMan® Array Human MicroRNA quantitative PCR was used to determine expression levels of 754 microRNAs in distal esophageal mucosa (1 cm above the gastro-esophageal junction) from 16 patients who had undergone ablation of non-dysplastic Barrett’s esophagus using argon plasma coagulation vs pretreatment mucosa, post-treatment proximal normal non-treated esophageal mucosa, and esophageal mucosal biopsies from 10 controls without Barrett’s esophagus. Biopsies of squamous mucosa were also taken from 5 cm above the pre-ablation squamo-columnar junction. Predicted mRNA target pathway analysis was used to investigate the functional involvement of differentially expressed microRNAs.RESULTSForty-four microRNAs were differentially expressed between control squamous mucosa vs post-ablation neosquamous mucosa. Nineteen microRNAs were differentially expressed between post-ablation neosquamous and post-ablation squamous mucosa obtained from the more proximal non-treated esophageal segment. Twelve microRNAs were differentially expressed in both neosquamous vs matched proximal squamous mucosa and neosquamous vs squamous mucosa from healthy patients. Nine microRNAs (miR-424-5p, miR-127-3p, miR-98-5p, miR-187-3p, miR-495-3p, miR-34c-5p, miR-223-5p, miR-539-5p, miR-376a-3p, miR-409-3p) were expressed at higher levels in post-ablation neosquamous mucosa than in matched proximal squamous and healthy squamous mucosa. These microRNAs were also more highly expressed in Barrett’s esophagus mucosa than matched proximal squamous and squamous mucosa from controls. Target prediction and pathway analysis suggests that these microRNAs may be involved in the regulation of cell survival signalling pathways. Three microRNAs (miR-187-3p, miR-135b-5p and miR-31-5p) were expressed at higher levels in post-ablation neosquamous mucosa than in matched proximal squamous and healthy squamous mucosa. These miRNAs were expressed at similar levels in pre-ablation Barrett’s esophagus mucosa, matched proximal squamous and squamous mucosa from controls. Target prediction and pathway analysis suggests that these microRNAs may be involved in regulating the expression of proteins that contribute to barrier function.CONCLUSIONNeosquamous mucosa arising after ablation of Barrett’s esophagus expresses microRNAs that may contribute to decreased barrier function and microRNAs that may be involved in the regulation of survival signaling pathways.

The effect of UV radiation from oxygen and argon plasma on the adhesion of organosilicon coatings on polypropylene

The influence of ultraviolet (UV) radiation from oxygen and argon pretreatment plasmas on a plastic substrate has not been fully understood yet. In particular, its influence on the adhesion properties has not been sufficiently researched so far. This paper addresses this issue by comparing the bond strength of a plasmapolymerized silicon organic coating (SiOxCyHz) on polypropylene (PP) after oxygen and argon plasma pretreatment and pretreatment by UV radiation emitted by the same plasmas. The UV radiation is isolated from the other species from the plasma by means of a magnesium fluoride (MgF2) optical filter. It could be shown that UV radiation originating from an oxygen plasma has a significant impact on both substrate surface chemistry and coating adhesion. The same maximum bond strength enhancement can be reached by pretreating the polypropylene surface either with pulsed oxygen plasma, or with only the UV radiation from this oxygen plasma. Also, similar surface chemistry and topography modifications are induced. For argon plasma no significant influence of its UV radiation on the substrate could be observed in this study.

Barrier SiO2-like coatings for archaeological artefacts preservation

Thin film chemical vapour deposition technique has been used for more than 50 years. Introducing organo-silicones as precursors, e.g. hexamethyldisiloxane (HMDSO) or tetraethyl orthosilicate (TEOS), brought new possibilities to this method. Barrier properties of thin films have become an important issue, especially for army and emergency services as well as for food and drink manufacturers. Our work is focused on protective HMDSO thin films for encapsulating cleaned archaeological artefacts, preventing the corrosion from destroying these historical items.Thin films are deposited via plasma enhanced chemical vapour deposition (PECVD) technique using low pressure capacitively coupled pasma in flow regime. Oxygen transmission rate (OTR) measurement was chosen as the most important one for characterization of barrier properties of deposited thin films. Lowest OTR reached for 50 nm thin film thickness was 120 cm3 m-2 atm-1 day-1. Samples were also analyzed by Fourier Transform Infrared spectrometry (FTIR) to determine their composition. Optical emission spectra and thin film thickness were measured during the deposition process. We optimized the deposition parameters for barrier layers by implementation of pulsed mode of plasma and argon plasma pre-treatment into the process.

Effect of different surface treatments and thermocycling on shear bond strength to polyetheretherketone

This study was designed to evaluate the shear bond strength of an adhesive/composite system subjected to different pretreated polyetheretherketone (PEEK) surfaces using different thermocycling conditioning methods. A total of 128 specimens were equally divided into four main groups ( n = 32/group): control (no pretreatment), air abrasion, argon plasma pretreatment, and femtosecond laser groups. The surface topographies and surface roughness were observed by atomic force microscopy after different pretreatments. The specimens were bonded with SE Bond/Clearfil AP-X™. All bonded specimens were stored in distilled water at 37°C for 24 h. Afterward, each group was divided into three subgroups ( n = 8/group) as follows: (a) stored in water for 56 h (37°C); (b) thermal aging for 5000 cycles (5°C/55°C); and (c) thermal aging for 10,000 cycles (5°C/55°C). The shear bond strengths were measured. Air abrasion, argon plasma pretreatment, and femtosecond laser significantly strengthened the bond of SE Bond/Clearfil AP-X™ to PEEK composite compared with that without additional pretreatment. In the same surface pretreatment, the shear bond strengths of specimens conditioned using water storage were higher than that using thermocycles (TCs). Additionally, the specimens with 5000 TC showed significantly higher shear bond strength than that with 10000 TC.

Synergistic Effect of Atmospheric Pressure Plasma Pre-Treatment on Alkaline Etching of Polyethylene Terephthalate Fabrics and Films

Dyeing of PET materials by traditional methods presents several problems. Plasma technology has received enormous attention as a solution for the environmental problems related with textile surface modifications, and there has been a rapid development and commercialization of plasma technology over the past decade. In this work, the synergistic effect of atmospheric pressure plasma on alkaline etching and deep coloring of dyeing properties on polyethylene terephthalate (PET) fabrics and films was investigated. The topographical changes of the PET surface were investigated by atomic force microscopy (AFM) images, which revealed a smooth surface morphology of the untreated sample whereas a high surface roughness for the plasma and/or alkaline treated samples. The effects of atmospheric pressure plasma on alkaline etching of the structure and properties of PET were investigated by means of differential scanning calorimetry (DSC), the main objective of performing DSC was to investigate the effect of the plasma pre-treatment on the Tg and Tm. Using a tensile strength tester YG065H and following a standard procedure the maximum force and elongation at maximum force of PET materials was investigated. Oxygen and argon plasma pre-treatment was found to increase the PET fabric weight loss rate. The color strength of PET fabrics was increased by various plasma pre-treatment times. The penetration of plasma and alkaline reactive species deep into the PET structure results in better dyeability and leaves a significant effect on the K/S values of the plasma pre-treated PET. It indicated that plasma pre-treatment has a great synergistic effect with the alkaline treatment of PET.

Surface modification of natural rubber latex films by hydroxyethyl methacrylate

The surface modifications of natural rubber latex films by argon plasma pretreatment, followed by UV-induced graft copolymerization of hydroxyethyl methacrylate, were carried out to improve the latex hydrophilicity. The effect of plasma pretreatment time, monomer concentration and UV irradiation time on the graft densities was studied. ATR-FTIR analyses indicates the efficient grafting of poly(hydroxyethyl methacrylate) onto the surface of latex film. The surface roughness of natural rubber latex films increases to 360 nm from 9 nm, leading to a decrease of water contact angle value of NR latex film surface to about 60° from 100°, and thus confirmed improvement of the hydrophilicity of latex film. Biocompatibility of the film was evaluated with vitro cytotoxicity test; the results proved a good biocompatibility of modified latex.

Inverted Pyramidal Texturing of Silicon Through Blisters in Silicon Nitride

We have demonstrated a novel process for the fabrication of inverted pyramidal structures on silicon. The proposed technique uses no photolithography step and is instead replaced by a thin-film deposition step and thermal annealing. In this paper, inductively coupled plasma CVD (ICP-CVD) silicon nitride was used as the thin film. Blisters were formed on the silicon nitride film upon annealing at 800 $^{\circ}$ C. The silicon nitride film remaining on the surface of the wafer acts as an etch mask for the texturization process, which is carried out in an alkaline solution. It was observed that only open blisters participated in the etch process, while closed blisters were resistant to the etching solution. It was observed that the gas flow ratio, annealing time, and temperature played an important role in determining the shape, size, and areal density of the blisters. By integrating an argon plasma pretreatment in the silicon nitride deposition process, surface coverage of 51% was obtained for lower annealing temperatures of 550 $^{\circ}$ C. Upon etching the sample in an alkaline solution, a weighted average reflectance of 17.3% was obtained, indicating the potential of this process.

Adhesion of Thin CVD Films on Pulsed Plasma Pre-Treated Polypropylene

The adhesion of thin CVD films on polyolefins is often critical due to the low surface free energy of the polymers. In this study, injection moulded PP samples are produced and investigated. The samples are treated in very well-characterized pulsed plasmas before a HMDSO-based coating is applied. The resulting bond strength is analyzed using pull-off tests. The fractured interfaces are characterized with XPS. Oxygen and argon plasma pre-treatments of the PP samples result in a bond strength improvement by a factor of about 2. Comparing oxygen and argon pre-treatments at equal ion fluences to the surface, it can be shown that the bond strength between CVD-coating and polymer is similar.

Properties of plasma-spray coated hydroxyapatite on carbon/carbon composites pretreated by an argon plasma

Carbon/carbon composites pretreated by an argon plasma were coated by hydroxyapatite (HA) using a plasma spraying method. The morphology, the compositions of the coating and bond strength between HA and substrate were investigated by scanning electron microscopy, X-ray diffraction, infrared spectrometry and a scratching test. Results indicate that although the morphology and phase compositions of the HA coating are similar, the substrate critical load, above which apparent spallation of the coating occurs, was 14.0 and 8.9 N with or without the pretreatment respectively, indicating that the argon plasma pretreatment improves the bond strength between the coating and the substrate. [New Carbon Materials 2013, 28(3): 215–221]