Cascade Arc Torch Research Articles

SiO x plasma thin film deposition using a low-temperature cascade arc torch

Plasma thin films were deposited from gas mixtures of hexamethyldisiloxane (HMDSO) and oxygen (O 2) using a low-temperature cascade arc torch (LTCAT). Various properties of the deposited HMDSO plasma coatings, including refractive index (RI), surface contact angle, and hardness were evaluated. The characterization results using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ellipsometry, and water contact angle measurements indicated that, with increased O 2 addition, the deposited HMDSO plasma thin films were of inorganic SiO x nature. It was also found that, in the LTCAT plasma system, O 2 addition significantly improves the hardness of the resulting HMDSO plasma coatings. The film hardness of the deposited HMDSO plasma coatings measured by a standard pencil test (ASTM D3363-05) reached 6H with increased O 2 addition in the HMDSO/O 2 gas mixture. Such hard plasma coatings could be potentially used for many important industrial applications, such as anti-scratch coatings on plastic glasses and various plastic lens materials.

The mesh disturbance effects in a low‐temperature cascade arc torch for surface modification of low density polyethylene

AbstractA stainless steel mesh was placed in a low‐temperature cascade arc torch (LTCAT) to study its disturbance effects on the plasmas and on the surface modification of low density polyethylene (LDPE). It was found that the photoemitting species were deflected by the screen and only faint glow was observed after the mesh. Optical emission spectroscopy examination indicated that the amount of electronically excited species in the plasma was greatly reduced after passing through the mesh. Grounding the mesh altered the nature of the discharge and a greater intensity of O emission was observed in Ar LTCAT + O2 discharge, which indicated greater energy transfer to the oxygen. Although a decrease in surface damage was observed on the treated LDPE samples by placement of the mesh in the Ar LTCAT discharges, the wettability achieved was also greatly reduced. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Surface modification of a group of polymers using a low temperature cascade arc torch

AbstractSurface modification treatments were performed on six different types of polymers using low temperature cascade arc torch (LTCAT) of Ar with or without adding reactive gas of O2 or H2O vapor. The effects of the treatments on the wettability enhancement, surface degradation from oligomer formation, and surface stability from the mobility of surface moieties and hydrophobic recovery were investigated. Surface characterization techniques included the static Sessile droplet method and dynamic Wilhelmy balance method. Experimental results indicated that Ar LTCAT treatments of the polymers with shorter treatment times (2 s in most cases) resulted in stable and hydrophilic surfaces without any surface damage from oligomer formation, with the exception of nylon‐6. The excellent results from Ar LTCAT treatments were attributed to the CASING effect (crosslinking via activated species of inert gas). Addition of O2 into Ar LTCAT resulted in greater wettability of the treated surfaces, but increased surface damage from oligomer formation. Adding H2O vapor into Ar LTCAT produced extremely hydrophilic surfaces on the polymers, but pronounced surface damage. The surface oligomer formation was attributed to alkoxy degradation reactions and chain scission from overexposure to high energy species. Comparisons of the treatment outcomes for each type of polymer are discussed with respect to the degree of wettability enhancement, the stability of the treated surfaces, and the susceptibility to degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Some Important Aspects of Plasma Polymerization

AbstractSummary: Some important aspects of the processing of plasma polymerization coating, which are not well known or well practiced, are discussed in a brief topical overview. Those aspects are the following: 1) power input parameters for diffuse luminous gas phase polymerization, DC cathodic polymerization, and low pressure cascade arc torch (LPCAT) polymerization, 2) ionization in negative glow versus molecular dissociation in dissociation glow (cathode glow), 3) influence of the deposition plasma on the substrate polymer, 4) types of plasma polymers, 5) importance of the amorphous nature of plasma polymers, 6) chemical reactions in beams versus in the gas phase, and 7) onion‐layered structure of the luminous gas phase and operation scale‐up.Glow discharges of Ar (left) and of an organic molecule (right).magnified imageGlow discharges of Ar (left) and of an organic molecule (right).

Durable bonding characteristics of thermoplastic olefins plasma-treated by low-temperature cascade arc torches

Low-temperature cascade arc torch (LTCAT) polymerization was applied to modify surface characteristics of thermoplastic olefins (TPOs). LTCAT has a unique feature that the activation of carrier gas (Ar) via creation of a plasma state and the deactivation of excited species that lead to surface modification or to the deposition of plasma polymer are spatially de-coupled. Consequently, the addition of a monomer or a reaction gas in the reaction chamber does not influence the first step of Ar plasma formation. The main active species in LTCAT are excited Ar neutrals, and no electric field exists in the reaction chamber. It was found that the beams of excited Ar neutrals are ideally suited for the surface modification of polymers because undesirable damage caused by the bombardment of energetic species can be avoided. The LTCAT of Ar was found to yield stable modification of TPO surfaces via post-plasma reaction of the treated surface with ambient oxygen. An excellent adhesion of a primer coating to surface of TPOs was obtained by treatment of the surface with Ar LTCAT, which passed the tape test after scribed samples were boiled in water for 8 h.

Surface modification of poly(tetrafluoroethylene) by a low‐temperature cascade arc torch and radio‐frequency plasmas

Surface modification of poly(tetrafluoroethylene) by a low‐temperature cascade arc torch and radio‐frequency plasmas

Surface modification of poly(tetrafluoroethylene) by a low-temperature cascade arc torch and radio-frequency plasmas

Poly(tetrafluoroethylene) (PTFE) films were treated with a low-temperature cascade arc torch (LTCAT) and radio-frequency (RF) plasmas of argon and hydrogen. The plasma-treatment effect on the PTFE surface was studied with contact-angle measurement and scanning electron spectroscopy (SEM). LTCAT argon plasma, which is recognized as a beam of excited argon neutrals, was very efficient at improving the surface hydrophilicity of PTFE. For both the LTCAT and RF operation, argon plasma was more effective at modifying the surface wettability of PTFE films than hydrogen plasma was. Furthermore, the sample positions (inside or beyond the glow region) had a strong impact on the efficiency of the plasma treatment. SEM surface images indicated that no significant morphology change was induced on the PTFE films exposed to a LTCAT and RF argon plasmas.

Internal stress in plasma polymer films prepared by cascade arc torch polymerization

Thin plasma polymer films were deposited from several liquid monomers (mainly siloxane-type monomers) in a low-temperature cascade arc torch (CAT) reactor. The effects of monomer structures and plasma parameters on internal stress in the films were experimentally studied. By appropriately adjusting these factors, the internal stress in the film was reduced nearly two orders of magnitude from 109 to 107 dyn/cm2. It was noted that the polymer films prepared from siloxane-type monomers showed lower internal stress than their hydrocarbon counterpart. Fourier transform-infrared spectroscopy (FTIR) studies indicated that a large amount of SiOSi structure from siloxane monomers, which are very flexible bonds, was preserved in the resultant plasma polymers. Ellipsometry results suggested that the internal stress can be qualitatively correlated with the refractive index of the plasma polymer film. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1577–1587, 1999

Deposition behavior in a low-temperature cascade arc torch (CAT) polymerization process

Two kinds of hydrocarbon type monomers and three kinds of organosilicons were polymerized by a low-temperature cascade arc argon plasma torch. Their deposition behaviors were studied as a function of experimental parameters and monomer elemental compositions. It was found that the normalized deposition rate (DR), expressed as deposition yield of DR/(FM)m, was determined by a composite operational parameter, W*(FM)c/(FM)m, where W is the power input, and (FM)c and (FM)m are the mass flow rates of carrier gases and monomers, respectively. Experimental results indicated that the deposition yield is highly dependent on the elementary compositions of monomers. Optical emission spectroscopy study on the argon plasma torch showed that the emission intensity of excited argon neutrals was proportional to the value of the parameter W*(FM)c. These results further certified that excited argon neutrals are the main energy carriers from the cascade arc column to activate monomers in the argon plasma torch. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 967–982, 1999

Optical emission diagnostics in cascade arc plasma polymerization and surface modification processes

Optical Emission Spectroscopy (OES) was used to identify reactive species and their excitation states in low-temperature cascade arc plasmas of N2, CF4, C2F4, CH4, and CH3OH. In a cascade arc plasma, the plasma gas (argon or helium) was excited in the cascade arc generator and injected into a reactor in vacuum. A reactive gas was injected into the cascade arc torch (CAT) that was expanding in the reactor. What kind of species of a reactive gas, for example, nitrogen, are created in the reactor is dependent on the electronic energy levels of the plasma gas in the cascade arc plasma jet. OES revealed that no ion of nitrogen was found when argon was used as the plasma gas of which metastable species had energy less than the ionization energy of nitrogen. When helium was used, ions of nitrogen were found. While OES is a powerful tool to identify the products of the cascade arc generation (activation process), it is less useful to identify the reactive species that are responsible for surface modification of polymers and also for plasma polymerization. The plasma surface modification and plasma polymerization are deactivation processes that cannot be identified by photoemission, which is also a deactivation process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1583–1592, 1998

Low-temperature cascade arc torch treatments for enhanced adhesion of primer to thermoplastic olefins

Improvement of primer adhesion to thermoplastic olefins (TPOs) by a low-temperature cascade arc torch treatment was investigated. A cascade arc was created with argon, and a treatment gas (air or methane) was added in the reaction chamber. It was found that the argon torch as well as the air/argon torch and the methane/argon torch can improve the primer adhesion to TPOs. Tape adhesion tests (ASTM method 3359-92a) demonstrated this improvement; a rating of “0” for untreated TPOs and “5” for air, methane, and argon torch-treated TPOs under certain operating conditions. Wettability of primer and of deionized water to TPOs were evaluated by contact angle measurements. TPO surface morphology was evaluated using scanning electron microscopy (SEM). The surface composition was characterized by using electron spectroscopy for chemical analysis (ESCA). The mechanism of improvement of primer adhesion to TPOs is discussed in this article. Primer adhesion was easily enhanced by the treatments for the soft and flexible TPOs (ETA-3041c and ETA-3101). Primer adhesion to hard and brittle TPOs (ETA-3183) was more difficult. Adhesion performance of primer to air, methane, and argon torch-treated TPOs was shown to have different mechanisms. For air plasma-treated surfaces, polar oxygen and nitrogen-containing groups were produced in the nonpolar surface layers, forming chemical bonds to TPOs; and plasma-etched pits spread all over the surface of TPOs into which the primer penetrated to form a mechanical interlock between TPOs and primer. For argon plasma-treated surfaces, the weak boundary layers (WBLs) of TPO surfaces were converted to a stronger layer by argon plasma, which resulted in enhancing primer adhesion to the surfaces of TPOs. The methane/argon torch allowed the deposition of a plasma polymer layer which replaces the weak boundary layer on untreated TPOs with a tightly crosslinked plasma polymer layer, and provides polar groups on the surface (by postplasma reaction of the residual free radicals with air). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:855–863, 1998

Penetration of plasma surface modification into porous media. III. Multiple samples exposed to CF4 and C2F4 low temperature cascade arc torch

AbstractThe depth and possible mechanisms of the penetration of surface modification into porous media by a low temperature cascade are torch are investigated. Two different modes of such penetration (“flow controlled” and “diffusion controlled”) are evaluated. Three porous samples [stacks of 10 sheets of nonwoven fabrics of poly(ethylene terephthalate)each], placed at an axial distance of 24, 28, and 32 cm from the cascade are anode, are exposed to a low temperature cascade arc torch containing argon and CF4 or C2F4, and surface properties of each of the sheets within treated porous samples are examined by ESCA. It is shown that interaction of chemically reactive species, created in the low temperature cascade arc torch, with the surface is not limited to the surface directly contacted by the torch. The flow controlled penetration is more pronounced for the outer layers, while diffusion controlled penetration is within the inner layers of the porous structure. Substantial differences in the fluorination effect of CF4 (nonpolymer forming gas) and C2F4 (polymer forming gas) discharges for the second and third stacks are observed, that can be explained by the fact that the major effect of the CF4 cascade arc torch treatment is based on the reaction of reactive species with the surface polymer molecules. The effect of C2F4 cascade arc torch treatment is based on the reactions of reactive species with polymers as well as reactions of reactive species themselves at the surface (plasma polymerization). Reactivity of the species created in C2F4 discharge is much higher compared to that created in CF4 discharge, which is one of the major factors influencing penetration trends of low temperature cascade arc treatment into porous media. © 1995 John Wiley & Sons, Inc.

Penetration of plasma surface modification. II. CF4 and C2F4 low‐temperature cascade arc torch

AbstractThe depth of surface modification by low‐temperature cascade arc torch is investigated. A stack of 10 sheets of nonwoven fabrics of polyester fibers is exposed to a low‐temperature cascade arc torch containing CF4 or C2F4, and the fluorination effect is examined by ESCA. It is shown that interaction of chemically reactive species, created in a low‐temperature cascade arc torch, with the surface is not limited to the surface contacted by the torch (flame). The results indicate that the fluorination effect is observed on surfaces which are shadowed from the torch by overlying fibers. The highest degree of fluorination is found on the second layer, rather than on the first layer which the torch contacts directly. No significant differences in the trends of penetration of CF4 and C2F4 treatment through porous samples are observed. However, ESCA data show principal differences in chemical structures of the surfaces treated with CF4 (nonpolymer‐forming gas) and C2F4 (polymer‐forming gas). These results indicate that chemically reactive species induced by the excited species of argon rather than primary species created by the ionization process seem to play predominant roles in the surface treatment as well as the low‐temperature cascade arc torch polymerization of perfluorinated compounds. © 1994 John Wiley & Sons, Inc.