Highly transparent (>80%) and conductive layers (10 -6 S/cm) were obtained by the pulsed plasma polymerization of thiophene. The influence of power, pressure, pulse time, duty cycle, and position in the reactor on the conductivity of the resulting plasma polymerized thiophene (PPT) layers was evaluated. In the used ranges, only pressure had a significant influence on the conductivity of the deposited layer. The results could be correlated to the effect of the deposition parameters on the fragmentation of the thiophene monomer. At high pressure there was less fragmentation of thiophene, resulting in a higher conductivity of the layer. It was shown that the use of a pulsed plasma as a means to minimize fragmentation is most efficient when the off time is chosen such that the reactor is replenished with new monomer during the off period.

A series of poly(ethylene) (PE) films with different degrees of crystallinity was treated with a radio-frequency tetrafluoromethane (CF4) gas plasma (48−49 W, 0.06−0.07 mbar, and continuous vs pulsed treatment). The etching behavior and surface chemical and structural changes of the PE films were studied by weight measurements, X-ray photoelectron spectroscopy (XPS), static and dynamic water contact angle measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM). With increasing crystallinity (14−59%) of PE, a significant and almost linear decrease of the etching rate was found, ranging from 50 Å/min for linear low-density poly(ethylene) (LLDPE) to 35 Å/min for high-density poly(ethylene) (HDPE). XPS analysis revealed that after CF4 plasma treatment the PE surfaces were highly fluorinated up to F/C ratios of 1.6. Moreover, CF4 plasma treatment of PE resulted in extremely hydrophobic surfaces. Advancing water contact angles up to 150° were measured for treated LDPE films. Both SEM and AFM analysis revealed that pronounced surface restructuring took place during prolonged continuous plasma treatment (≥15 min). The lamellar surface structure of LDPE changed into a nanoporous-like structure with uniform pores and grains on the order of tens of nanometers. This phenomenon was not observed during plasma treatment of HDPE films. Apart from surface roughening due to selective etching, pulsed plasma treatment did not result in significant surface structural changes either. Therefore, the restructuring of continuously plasma-treated surfaces was attributed to a combined effect of etching and an increase of the surface temperature, resulting in phase separation of PE-like and poly(tetrafluoroethylene)-like material, of which the latter is surface oriented.

SYNOPSISPoly(ethy1ene) (PE) films were treated with a carbon dioxide (CO,) plasma to study the formation of oxygen-containing functional groups at the surface. Modified and nonmodified films were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. During the C02 plasma treatment, the PE surface is etched and oxidized, yielding films with a very hydrophilic surface. The oxygen incorporation at the surface is fast and can be described by a combination of a zero-order incorporation and a first-order etching process. Several oxygen functionalities such as carboxylic acid (approximately 14% of the oxygen present), ketone/aldehyde (25%), and hydroxyl/epoxide (5-9%) groups were introduced at the surface by the plasma treatment. This was shown by using derivatization reactions for specific functional groups followed by X P S analysis. The wettability of the plasma-treated surfaces decreased when the films were stored for prolonged periods of time in air. This aging process could not be completely reversed by immersion of the films in water. 0 1995 John Wiley & Sons, Inc.

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