Argon Glow Discharge Plasma Research Articles

Improving osteogenic properties of zirconia ceramic via glow discharge plasma-enhanced deposition of amine organic compound

Background/purposeOsseointegration potential is greatly depended on the interaction between bone cells and dental implant surface. Since zirconia ceramic has a bioinert surface, functionalization of the surface with an organic compound allylamine was conducted to overcome its drawback of minimal interaction with the surrounding bone. Materials and methodsThe zirconia surface was initially treated with argon glow discharge plasma (GDP), then combined with amine plasma at three different conditions of 50-W, 75-W and 85-W, to prepare the final samples. The surface characteristics and cell biocompatibility were then evaluated. ResultsSurface morphology analysis revealed a bulbous pattern on allylamine-treated sample groups. The aromatic C–H, C–O, N–H, C ˆ C, and C–H stretching and functional groups have been identified. Surface roughness increased, and hydrophilicity improved after surface modification. Cell viability analysis showed the highest result for the allylamine 50-W (A50) group. Alkaline phosphatase (ALP) assay indicated the A50 group had the highest activity, subsequently promoting late-stage mineralization at day 21. The reverse transcription-quantitative polymerase chain reaction (RT-qPCR) data demonstrated a significant upregulation of osteogenic gene expressions from day 1 to day 21. ConclusionThe allylamine-treated surface demonstrates immense enhancement in the surface hydrophilicity as well as in the viability, differentiation, and osteogenic properties of osteoblast-like cells. This makes it a promising candidate for future dental implant applications.

SPECTROSCOPIC INVESTIGATION OF ARGON DC GLOW DISCHARGE IN PLASMA MEDIUM

In this study, UV-VIS-NIR (Ultraviolet Visible Near-Infrared) spectra emitted from Argon Glow discharge plasma in a low vacuum were recorded with a high-resolution Czerny-Turner type spectrometer. Argon plasma was produced at a pressure of 5mTorr and with a voltage of 584 V. Argon plasma was produced between two parallel stainless steel plates anode and cathode with a diameter of 15 cm, a thickness of 0.8 cm, and a distance of 13 cm between them. The radiative and collisional processes of the Argon plasma medium were modeled by the PrismSPECT atomic physics software (Software). The distributions of ion densities were calculated using the Saha-Boltzmann equation. The intensity of the excited energy levels of Ar(I) and Ar (II) ions were calculated in the electron temperature range of (0.4-3.5eV) and the mass density of (10-4-10-1gr/cm3). The UV-Visible-NIR spectra were simulated and compared with experimental spectra. The ratios of the intensities of the ArII/ArI (1s22s22p63s23p44f1/1s22s22p63s23p54p1) spectral lines were obtained for different plasma temperatures and densities. The temperature of the argon plasma was obtained from the spectral line intensity ratios.

Transition of a 2D crystal to a non-equilibrium two-phase coexistence state

In this paper, we present experimental observation of the transition of a 2D dust crystal to a non-equilibrium solid–liquid phase coexistence state. The experiments have been carried out in an L-shaped dusty plasma experimental device in a DC glow discharge argon plasma environment. Initially, a monolayer crystalline structure is formed, which is later transformed to a two-phase coexistence state using the background neutral pressure as a control parameter. Self-excited horizontal oscillations are found in the center of the monolayer prior to the appearance of the coexistence state. It is observed that a molten center coexists with a solid periphery. Various structural, thermodynamic, and dynamical quantities are used to characterize the phase state. The surface tension at the solid–liquid circular interface is also determined. A detailed parametric study is made to delineate the existence region of such a state. It is found that melting caused at the core is due to the onset of a localized Schweigert instability in the presence of a few stray particles beneath the top layer in that region.

Confinement controlled dynamical structural rearrangement in a quasi-2D dusty plasma crystal

In this work, we present experimental results on the structural transition of a two-dimensional dust crystal through controlled adjustment of its radial confinement while keeping all other discharge parameters constant. The experiments are performed in an L-shaped Dusty Plasma Experimental device in a DC glow discharge argon plasma environment. Initially, a purely 2D dust crystal is formed inside a circular confining ring at the interface of the plasma-cathode sheath region. This monolayer with a hexagonal lattice configuration of the dust particles gets buckled when the sheath thickness around the radial confinement ring is reduced. A bilayer with a square lattice configuration emerges in the dust system due to the onset of a transverse instability. The multiple crystalline domains at this lower confinement show signatures of a constant structural rearrangement in the system. The timescale associated with this rearrangement is quantified from the bond-orientational correlation function. It is found that the heterogeneous cooperative micro-motion of particles in the quasi-layered system is responsible for the rearrangement over the passage of time.

Kelvin-Helmholtz instability in a compressible dust fluid flow

We report the first experimental observations of a single-mode Kelvin-Helmholtz instability in a flowing dusty plasma in which the flow is compressible in nature. The experiments are performed in an inverted Pi-shaped dusty plasma experimental device in a DC glow discharge Argon plasma environment. A gas pulse valve is installed in the experimental chamber to initiate directional motion to a particular dust layer. The shear generated at the interface of the moving and stationary layers leads to the excitation of the Kelvin-Helmholtz instability giving rise to a vortex structure at the interface. The growth rate of the instability is seen to decrease with an increase in the gas flow velocity in the valve and the concomitant increase in the compressibility of the dust flow. The shear velocity is further increased by making the stationary layer to flow in an opposite direction. The magnitude of the vorticity is seen to become stronger while the vortex becomes smaller with such an increase of the shear velocity. A molecular dynamics simulation provides good theoretical support to the experimental findings.

Influence of low-pressure Ar plasma modification of Musa sapientum banana fibers on banana fiber reinforced epoxy composite

ABSTRACT Banana fibers are cost-effective, abundantly available and environmentally sustainable, but they often have some drawbacks, such as hydrophilicity and performance variations. The experimental approach is intended to be used in this work to examine the effects of cold glow discharge argon plasma modification on the surface of banana fibers. The emphasis is on examining the mechanisms that underlie the morphological and chemical changes observed in banana fibers, as well as identifying the mechanisms that enhance the fiber–matrix interface and, as a consequence, the mechanical properties of the laminates. Significant improvements were observed for epoxy matrix laminates reinforced with banana fibers when the surface of the banana fibers was modified by plasma of argon gas (Ar) gas with varying power densities of 80,120 W for 30 min, which changed the surface chemical characteristics. The FTIR and XRD investigations revealed that plasma treatment imparted active functional groups onto the surface of the banana fiber, establishing chemical interactions with the epoxy resin. As a result, banana fibers and modified BFREC composites can be used to manufacture interior panels, headliners, seatbacks, dashboards, automobile industry, and industrial applications in order to nurture self-sustaining biodegradable natural resources.

Trapping of waves in a flowing dusty plasma

We report on experimental observations of trapping of waves in a flowing dusty plasma. The experiments are performed in an inverted ∏-shaped dusty plasma experimental device in which the dusty plasma is created in a DC glow discharge argon plasma using micrometer-sized kaolin particles. Two copper wires are installed radially on the cathode, which serve to generate the flow in the dust fluid as well as to confine the waves. The dust fluid is initially made to flow over both the wires by altering the sheath potential of one of these wires, and as a result, the wave gets excited and propagates in the downstream direction. The wave gets trapped in between the wires when their separation is below a critical value of ∼2 cm. For a long time (of the order of a few seconds), the trapped-wave structure retains its identity. The amplitude of the wave crests and the distance between them remain constant with the dust fluid flow velocities. A numerical solution of the forced Korteweg-de Vries equation with two source terms as well as molecular dynamic simulations reproduce our experimental findings in a qualitative manner.

Square Lattice Formation in a Monodisperse Complex Plasma.

We present the first observations of a square lattice formation in a monodisperse complex plasma system, a configurational transition phenomenon that has long been an experimental challenge in the field. The experiments are conducted in a tabletop L-shaped dusty plasma experimental device in a dc glow discharge Argon plasma environment. By a careful control of the vertical potential confining the charged particles as well as the strength of the ion wake charge interactions with the dust particles, we are able to steer the system toward a crystalline phase that exhibits a square lattice configuration. The transition occurs when the vertical confinement strength is slightly reduced below a critical value leading to a buckling of the monodisperse hexagonal 2D dust crystal to form a narrowly separated bilayer state (a quasi-2D state). Some theoretical insights into the transition process are provided through molecular dynamics simulations carried out for the parameters relevant to our experiment.

Mechanical and surface characterization of sisal fibers after cold glow discharge argon plasma treatment

Mechanical and surface characterization of sisal fibers after cold glow discharge argon plasma treatment

Damage evolution behavior of cold plasma treated glass fiber/vinyl ester resin composites under bending load by acoustic emission

This study reveals the preparation and mechanical characterization of cold plasma treated glass fiber/vinyl ester resin composites. The surface characteristics and bending failure mechanism of composites treated by oxygen, argon and nitrogen glow discharge plasma were studied by acoustic emission. The results showed that the bending resistance of argon plasma treated glass fiber reinforced composites exhibited highest. The composite treated by oxygen plasma produced AE signals with a frequency of more than 300 kHz, indicating that the fiber was damaged and the material was brittle, which reduced the strength and plasticity of the material. The bending stress in warp direction was greater than that in weft direction. The bending resistance of the cold plasma treated glass fiber/vinyl ester resin composites was the highest under the conditions of power 150W, flow rate 10sccm and time 120s.

Investigating the Cold Plasma Surface Modification of Kaolin- and Attapulgite-Bound Zeolite A

Hydrophilic zeolites with low catalytic activity are considered as suitable adsorbents for drying gas streams containing olefinic compounds. In this contribution, the surface treatment of kaolin and attapulgite/zeolite A extrudates is investigated using argon glow discharge plasma. The zeolite is synthesized from kaolin using the hydrothermal method. Surface and bulk characterization is performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 physisorption, Fourier-transform infrared (FT-IR) spectroscopy, temperature-programmed-desorption (TPD) of NH3 and X-ray photoelectron spectroscopy (XPS) techniques. Plasma treatment increases surface area and pore volume, but it decreases the weak acidic site density of the extrudates. The obtained results show that attapulgite/zeolite extrudates are more affected by plasma treatment than kaolin/zeolite extrudates. The catalytic activity of untreated and plasma-treated extrudates are compared with respect to coke formation resulting from 1-butene and 1,3-butadiene. The plasma-treated sample is more resistant to coke formation (∼35% decrease compared to untreated one). The potassium contents of extrudates decreased as a result of sputtering loosely bound potassium cations on the crystal surface by argon ions, which led to a decrease in water sorption capacity (by ∼15% of the initial sorption capacity).

Thermodynamics and self-organization of strongly coupled Coulomb clusters: An experimental study

In this experimental work, the thermodynamics and self-organization of classical two-dimensional Coulomb clusters are studied as a function of the cluster size. The experiments are carried out in a DC glow discharge argon plasma in the dusty plasma experimental device for clusters with different number of particles. Hexagonal symmetry around each individual particle is quantified using the local orientational order parameter (|ψ6|) for all the configurations. The screened Coulomb coupling parameter, which plays a key role in determining the thermodynamic nature of a Coulomb cluster, is estimated using Langevin dynamics and found to be sensitive to the number of particles present in the cluster. In addition, the process of self-organization and the dynamics of individual particles of the cluster as it changes from a metastable state to the ground state are examined through the estimation of dynamic entropy. Our findings suggest an intimate link between the configurational ordering and the thermodynamics of a strongly coupled Coulomb cluster system—an insight that might be of practical value in analyzing and controlling the microdynamics of a wider class of finite systems.

Surface Modified \u03b2-Tricalcium phosphate enhanced stem cell osteogenic differentiation in vitro and bone regeneration in vivo

A major number of studies have demonstrated Beta-tricalcium phosphate (β-TCP) biocompatibility, bioactivity, and osteoconductivity characteristics in bone regeneration. The aim of this research was to enhance β-TCP's biocompatibility, and evaluate its physicochemical properties by argon glow discharge plasma (GDP) plasma surface treatment without modifying its surface. Treated β-TCP was analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis, and Fourier transform infrared spectroscopy characterization. To evaluate treated β-TCP biocompatibility and osteoblastic differentiation, water-soluble tetrazolium salts-1 (WST-1), immunofluorescence, alkaline phosphatase (ALP) assay, and quantitative real-time polymerase chain reaction (QPCR) were done using human mesenchymal stem cells (hMSCs). The results indicated a slight enhancement of the β-TCP by GDP sputtering, which resulted in a higher Ca/P ratio (2.05) than the control. Furthermore, when compared with control β-TCP, we observed an improvement of WST-1 on all days (p < 0.05) as well as of ALP activity (day 7, p < 0.05), with up-regulation of ALP, osteocalcin, and Osteoprotegerin osteogenic genes in cells cultured with the treated β-TCP. XPS and SEM results indicated that treated β-TCP’s surface was not modified. In vivo, micro-computed tomography and histomorphometric analysis indicated that the β-TCP test managed to regenerate more new bone than the untreated β-TCP and control defects at 8 weeks (p < 0.05). Argon GDP treatment is a viable method for removing macro and micro particles of < 7 μm in size from β-TCP bigger particles surfaces and therefore improving its biocompatibility with slight surface roughness modification, enhancing hMSCs proliferation, osteoblastic differentiation, and stimulating more new bone formation.

Synthesis and Surface Characterization of PMMA Polymer Films in Pure Oxygen, Argon, and Nitrogen Glow Discharge Plasma

The anticorrosion effect and biocompatibility property of Poly (methyl methacrylate) (PMMA) materials have been used in a variety of commercially available products and medical devices for many years. In this work, the treatment of surfaces prepared PMMA films by oxygen, argon and nitrogen plasma, requires understanding the effect of low energy ions on the surface modification of the film of PMMA. Due to this, the samples of prepared PMMA were exposed to three different gases at the same discharge conditions. Changes within the morphology and surface hydrophilicity of the treated samples were characterized by optical microscope images and the measurements of contact angle. Treatment of PMMA with O2, N2, Ar gases displayed a decreasing in the contact angle that results in increasing surface free energy. Oxygen –plasma treatment of PMMA films leads to high aspect ratio topography, with increased roughness for (5-30) minute process durations.

Excitation of dust acoustic shock waves in an inhomogeneous dusty plasma

An experimental investigation of the propagation characteristics of shock waves in an inhomogeneous dusty plasma is carried out in the dusty plasma experimental device. A homogeneous dusty plasma, made up of poly-dispersive kaolin particles, is initially formed in a direct current glow discharge argon plasma by maintaining a dynamic equilibrium of the pumping speed and the gas feeding rate. Later, an equilibrium density inhomogeneity in the dust fluid is created by introducing an imbalance in the original dynamic equilibrium. Non-linear wave structures are then excited in this inhomogeneous dusty plasma by a sudden compression in the dust fluid. These structures are identified as shock waves, and their amplitude and width profiles are measured spatially. The amplitude of a shock structure is seen to increase, whereas the width broadens as it propagates down a decreasing dust density profile. A modified-Korteweg–de Vries–Burger equation is derived and used to provide a theoretical explanation of the results, including the power law scaling of the changes in the amplitude and width as a function of the background density.

Experimental observation of a first-order phase transition in a complex plasma monolayer crystal

The formation and melting of a monolayered charged dust particle crystal in a DC glow discharge argon plasma is studied. The nature of the melting or formation process is established as a first-order phase transition from the variations in the Coulomb coupling parameter, the dust temperature, the structural order parameter, and from the existence of a hysteresis behavior. Our experimental results are distinctly different from existing theoretical predictions for two dimensional crystals based on the Kosterlitz-Thouless-Halperin-Nelson-Young mechanism or the grain boundary induced melting and indicate a mechanism that is akin to a fluctuation induced first-order phase transition in complex plasmas.

Measurement of temperature of a dusty plasma from its configuration

AbstractA new concept called “configurational temperature” is introduced in the context of dusty plasma, where the temperature of the dust particles submerged in the plasma can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles, which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two‐dimensional (2D) OpenMP parallel molecular dynamics and Monte Carlo simulation and then compared with the temperature evaluated from experimental data. The experiment have been carried out in the Dusty Plasma Experimental (DPEx) device, where a 2D stationary plasma crystal of melamine formaldehyde particles is formed in the cathode sheath of a DC glow discharge argon plasma. The kinetic temperature of the dust is calculated using the standard particle image velocimetry technique at different pressures. An extended simulation result for the three‐dimensional case is also presented, which can be employed for the temperature measurement of a three‐dimensional dust crystal in laboratory devices.

Radiation shielding and physical properties of lead borate glass-doped ZrO2 nanoparticles

Zirconium oxide (ZrO2) nanoparticles have been prepared and examined by XRD. The transparent lead alkali borate glass systems of formula xZrO2–20PbO2–(80 − x)·Na2B4O7 (0 ≤ x ≤ 24 mol%) are prepared by melting quench method and doped by zirconia nanoparticles. Deconvolution of its FTIR reveals to increase the N4 fraction boron atoms. This result reveals the Zr4+ which forms BO4 network units. The density and refractive index of chosen glass are increased due to add of ZrO2 nanoparticles. Both ultrasonic velocities (longitudinal vL and shear vT) increase with the ZrO2 content increase. The packing density, bulk modulus and Young’s modulus increase with increasing of ZrO2 nanoparticle content. The attenuation coefficients of the studied glasses have been measured at different energies (356, 662, 1173 and 1332 keV) using narrow beam transmission geometry. The obtained results indicated that, the values of the mass attenuation coefficient (µm), the effective atomic number (Zeff) and effective electron density (Nel) of the glass samples decreased with the increase in the ZrO2 concentration at the energies (662,1173and 1332 keV), while these parameters (µm, Zeff and Nel) increased with the increase in the ZrO2 concentration at 356 keV. The samples are irradiated 30 min by argon glow discharge plasma (GDP). The values of optical band gap decreased slowly with ZrO2 nanoparticles increased and after plasma irradiation.

Low-temperature plasma treatment of polylactic acid and PLA/HA composite material

Investigations of the surface physicochemical properties of polylactic acid and polylactic acid/hydroxyapatite composite in a 70/30 ratio modified by atmospheric pressure low-temperature glow discharge argon plasma with the pulse duration of 1 μs and 5 μs and repetition rate of 100 kHz are described. Plasma modification of such materials may significantly affect physicochemical properties of surface. The polymerization of l-lactide was carried out at a temperature of 155 °C for 6 h. X-ray diffraction analysis shows that the degree of crystallinity of polylactic acid and composites based on polylactic acid/hydroxyapatite composite increases after plasma treatment due to polymer chain disruption. Infrared spectroscopy indicates that the –C=O absorption band intensity increases with plasma pulse duration, in turn indicating oxidation processes occurring in the polylactic acid surface layers. The wettability characteristics of the materials are improved by the plasma treatment, resulting in decreased water, glycerol, and ethylene glycol contact angle, and enhanced free surface energy.

Experimental verification of modified Paschen’s law in DC glow discharge argon plasma

Breakdown voltage of a gas is the required voltage to start a discharge or electric arc through the gas. Paschen’s law describes the characteristics of gas breakdown voltage between two electrodes. This law states that the Gas breakdown voltage(VB) depends only on the product of gas pressure (p) and gap length(d) between electrodes (VB=f(pd)). In this paper, the effect of electrode separation length(d) and electrode radius (r) on gas breakdown voltage is studied experimentally. A gas discharge system with a large gap length compared to electrode radius is used for the study. Paschen curves are plotted for different electrode separation lengths and electrode radii. It is observed that gas breakdown voltages deviates from Paschen’s law and depend on the d/r ratio also in addition to the product of gap separation and pressure, i.e. VB=f(pd,d/r). This relation, already reported in the analyses of micro gap discharge and theoretical studies, is known as modified Paschen’s law. In order to experimentally verify the modified Paschen’s law in large discharge gaps, many experiments are conducted by varying both electrode separation and electrode radii but keeping the d/r ratio always same. It is observed that for different discharge system geometries, if d/r ratio is same, the break down voltages are same for same pd value. The Paschen’s curves are also plotted for different experiments and it is observed that the curves overlap if d/r ratio is set same for all experiments. Thus, the work presented in this paper experimentally verify the modified Paschen’s law.