title: Correlation between the plasma characteristics and the surface chemistry of plasma-treated polymers through partial least-squares analysis.
abstract: We investigated the effect of various plasma parameters (relative density of atomic N and H, plasma temperature, and vibrational temperature) and process conditions (pressure and H2/(N2 + H2) ratio) on the chemical composition of modified poly(tetrafluoroethylene) (PTFE). The plasma parameters were measured by means of near-infrared (NIR) and UV-visible emission spectroscopy with and without actinometry. The process conditions of the N2-H2 microwave discharges were set at various pressures ranging from 100 to 2000 mTorr and H2/(N2+H2) gas mixture ratios between 0 and 0.4. The surface chemical composition of the modified polymers was determined by X-ray photoelectron spectroscopy (XPS). A mathematical model was constructed using the partial least-squares regression algorithm to correlate the plasma information (process condition and plasma parameters as determined by emission spectroscopy) with the modified surface characteristics. To construct the model, a set of data input variables containing process conditions and plasma parameters were generated, as well as a response matrix containing the surface composition of the polymer. This model was used to predict the composition of PTFE surfaces subjected to N2-H2 plasma treatment. Contrary to what is generally accepted in the literature, the present data demonstrate that hydrogen is not directly involved in the defluorination of the surface but rather produces atomic nitrogen and/or NH radicals that are shown to be at the origin of fluorine atom removal from the polymer surface. The results show that process conditions alone do not suffice in predicting the surface chemical composition and that the plasma characteristics, which cannot be easily correlated with these conditions, should be considered. Process optimization and control would benefit from plasma diagnostics, particularly infrared emission spectroscopy.
authors: Laboratoire d'Ingénierie de Surface, Département de Génie des Mines, de la Métallurgie et des Matériaux, Centre de Recherche sur les Matériaux Avancés, Université Laval , 1065 avenue de la Médecine, Québec, Canada G1V 0A6.
authors: Maryam
authors: M
authors: Mavadat
authors: Massoud
authors: M
authors: Ghasemzadeh-Barvarz
authors: Stéphane
authors: S
authors: Turgeon
authors: Carl
authors: C
authors: Duchesne
authors: Gaétan
authors: G
authors: Laroche
mesh_terms: D016018:Least-Squares Analysis; D015999:Multivariate Analysis; D058626:Plasma Gases / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D014732:Vibration
chemical_list: D058626:Plasma Gases; D011108:Polymers