Plasma-structure dependence of the growth mechanism of plasma-polymerized fluorocarbon films with residual radicals

Abstract

Plasma-polymerized fluorocarbon polymer films are thought to contain a high density of residual radicals which are easily oxidized in air. The rf discharge power dependence of the oxidation rate in C3F6 plasma-polymerized films under an accelerating aging condition of 65 °C/85%RH was studied to estimate the density of residual radicals in the film. The corresponding discharge-power dependence of the plasma structure was also investigated by an effluent mass spectrometry. A critical discharge power was found where the oxidation rate and the plasma structure exhibit substantial changes. X-ray photoelectron spectra showed that the surface of the plasma-polymerized films prepared below the critical discharge power exhibited an excellent oxidation durability as a sputtered film of polytetrafluoroetylene. The films prepared above the critical power exhibited a high oxidation rate. An increase in –C– peaks in the C 1s spectra also suggested defluorination as well as oxidation. The secondary ion mass spectrum for the internal region of the aged plasma-polymerized films prepared above the critical discharge power contained oxidized CxFy species, while the spectra for the aged films prepared below the critical power contained no oxidation-related peaks. Concerning the mass spectra of the C3F6 plasma, high-mass species over 100 amu, including gas phase polymerization products such as C4F7 and C4F8, were predominant below the critical discharge power. Above the critical power, these high-mass species were rather decomposed, and the intensity decreasing with increasing discharge power. Simultaneously, the intensities of the small fragments such as CF, CF2, and CF3 increased with discharge power, causing about 50% of the total pressure increase. The films obtained under such a fragmentation predominant condition contained a higher density of residual radicals, resulting in a deterioration of the oxidation durability.

Low pressure plasma modifications for the generation of hydrophobic coatings for biomaterials applications

“…Defluorination behavior was also shown by C 3 F 6 pp when subjected to aging at 65°C/85% RH for 700 h . A critical P during ppt influenced the oxidation resistance of this pp.…”

“…Aging studies of pfps have been carried out at ambient or under accelerated conditions . Regardless of the environment, the aging mechanisms were similar in certain respects.…”

Mechanical Characterization of Methanol Plasma Treated Fluorocarbon Ultrathin Films Through Atomic Force Microscopy

“…Figure 3 shows high resolution XPS spectra for C(1s) of the unmodified CF x coating (a) and CF x coatings after 30 and 90 s methanol plasma treatments. The C(1s) spectra of the CF x films are fitted with five spectral components, as assigned to C-H/C-C-(BE = 285 eV), C-CF/C-O (BE = 287), CF/C=O (BE = 289.5 eV), -CF 2 (BE = 292), and CF 3 (BE = 294 eV) groups, according to literature (Horie, 1995;Mackie et al, 1997;Bourgoin et al, 1999;Boehm, 2002). As a percentage of oxygen lower than 1% was detected at the surface of the untreated CF x coating, no attribution due to C-O (286.9) or C=O (288.1) is proposed, while for methanol treated samples, peaks at BE = 287 and 289.5 can be attributed to oxygen containing groups.…”

Role of the surface chemistry of plasma polymer layers on their long‐term antifogging behavior

“…Surface rearrangement of the polymeric chains is frequently investigated by air/ WCAs measurement [19,20] whereas postoxidation due to free radicals in the plasma coatings, by X-ray photoelectron spectroscopy (XPS). [21][22][23] Thus, in this study, thermal stability and wet surrounding resistance of hydrophilic/oleophobic plasma films deposited on polycarbonate (PC) substrates are carried out by wettability measurements and XPS analysis. The antifogging properties of aged surfaces are also examined by the water vapor contact test.…”