Satomi Tajima

Effect of reactive species on surface crosslinking of plasma-treated polymers investigated by surface force microscopy

Polymer surface modification by ions, uncharged particles, and photons of inductively coupled Ar plasma was investigated with a surface force microscope. Optical windows consisting of crystals with different cutoff wavelengths and a metal shield were used to deconvolute the effects of the various plasma species on the modification of the surface nanomechanical properties of polyethylene. The extent of surface crosslinking was related to the frictional energy dissipated during nanoscratching. It is shown that surface crosslinking is primarily due to the simultaneous effects of uncharged particles and vacuum ultraviolet photons, while the ion bombardment effect is secondary.

Dependence of nanomechanical modification of polymers on plasma-induced cross-linking

The nanomechanical properties of low-density polyethylene (LDPE) modified by inductively coupled, radio-frequency Ar plasma were investigated by surface force microscopy. The polymer surface was modified under plasma conditions of different ion energy fluences and radiation intensities obtained by varying the sample distance from the plasma power source. Nanoindentation results of the surface stiffness versus maximum penetration depth did not reveal discernible differences between untreated and plasma-treated LDPE, presumably due to the small thickness of the modified surface layer that resulted in a substrate effect. On the contrary, nanoscratching experiments demonstrated a significant increase in the surface shear resistance of plasma-modified LDPE due to chain cross-linking. These experiments revealed an enhancement of cross-linking with increasing ion energy fluence and radiation intensity, and a tip size effect on the friction force and dominant friction mechanisms (adhesion, plowing, and microcutti...

Effect of ion energy fluence on the topography and wettability of low-density polyethylene exposed to inductively coupled argon plasma

The topography and wettability of low-density polyethylene (LDPE) were modified by an inductively coupled Ar plasma. The extent and mechanisms of surface modification were correlated with the ion energy fluence, determined from the ion density measured with a Langmuir probe. The ion energy fluence was varied in the range of (0.3–6.3) × 105 J m−2 by changing the sample distance from the plasma power source. Physical and chemical changes of the plasma-treated LDPE surfaces were evaluated with an atomic force microscope, goniometer and x-ray photoelectron spectrometer. Images of plasma-treated and chemically etched LDPE surfaces provided insight into the mechanisms responsible for the topography changes observed at different length scales in terms of the sample distance (ion energy fluence). A significant effect of the nanoscale roughness on the contact angle of LDPE was observed for high ion energy fluence. The results demonstrate a strong effect of the ion energy fluence on the modification of the surface morphology and wettability of plasma-treated polymer surfaces.

Optical and electrical characterization of pulse-modulated argon atmospheric-pressure inductively coupled microplasma jets

The critical parameters determining the generation of the pulse-modulated argon atmospheric-pressure inductively coupled plasma (AP-ICP) microjet were studied by varying the power, P, pulse-modulation frequency, f, and duty ratio, DR. The temporal changes in the net output power, Pnet, monitored between the very high frequency power supply and matching network by an rf sampler, and ArI 4s′[1/2]1O–4p′[1/2]0 emission from the antenna were measured to elucidate the behavior of this plasma. The AP-ICP microjet, which produces high-density (0.9–1.1×1015 cm−3) nonequilibrium plasma, consists of an alumina discharge tube with the inner diameter of 0.8 mm. The generation diagram of the pulse-modulated plasma was created by having f as the horizontal axis and DR as the vertical axis while varying P up to 50 W. At f≤10 kHz, the plasma was generated at above the linear lines of f and DR, which indicated the existence of the critical power-off period of approximately 80 μs. At f>10 kHz, the pulse-modulated plasma was...

Evaluation of the difference in the rate coefficients of F2 + NOx (x = 1 or 2) → F + FNOx by the stereochemical arrangement using the density functional theory.

The rate coefficient of F2 + NO → F + FNO is 2 to 5 orders of magnitude higher than that of F2 + NO2 → F + FNO2 even though bond energies of FNO and FNO2 only differ by ∼0.2 eV. To understand the cause of having different rate coefficients of these two reactions, the change in total energies was calculated by varying the stereochemical arrangement of F2 with respect to NOx (x = 1 or 2) by the density functional theory (DFT), using CAM-B3LYP/6-311 G+(d) in the Gaussian program. The permitted approaching angle between the x-axis and the plane consisting of O, N, F, and ϕ plays a key role to restrict the reaction of NO2 and F2 compared to the reaction of NO and F2. This restriction in the reaction space is considered to be the main cause of different rate coefficients depending on the selection of x = 1 or 2 of the reaction of F2 + NOx → F + FNOx, which was also confirmed by the difference in Si etch rate using the F formed by those reactions.