Summary: In this paper, the gas phase composition of hexamethyldisiloxane (HMDSO) microwave plasma at 4 × 10−3 mbar and of the corresponding films were studied by FTIR spectroscopy under different power conditions. At low powers, species with a chemical structure very similar to that of HMDSO were observed in the gas phase, whereas the film essentially contained short [(CH3)2SiO]n‐like chains with a low branching rate and the end group Si(CH3)3. At higher powers, the chemical entities present in the gas phase contained several (SiO)x bonds, whereas the branching rate in the film increased with the amount of SiH, SiC and SiO bonds. The interpretation of these observations led to a proposal involving a chemical mechanism. In this mechanism, the increasing decomposition of HMDSO into by‐products, which themselves increasingly decompose as the power is raised, plays a determining role.

Experiments on polystyrene films formed by a glow-discharge technique shows a reproducible bistable switching. Various interpretations are briefly reviewed. It is shown that the resistance of the on state is strictly related to the energy needed by the on-off transition. From the value of this energy it is concluded that the most probable explanation is that the on current takes place along a filamentary path constituted by carbon atoms. A quantitative analysis is made on the basis of the heat balance equation. Formation of carbonated chains is confirmed by a chromatography analysis in vapor phase which shows an hydrogen release.

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Reproducible bistable switching has been observed in Au-Polymer-Au junctions. The polymer is formed by a glow-discharge polymerization technique. The resistance ratio is more than 107 and structures can be switched more than 2000 times. When the polymer thickness is lower than 1500 Å, the threshold voltage increases linearly with the polymer thickness. A scanning electron microscope picture of a junction that has been switched shows circular dots, ranging between 5- and 10- μm diameter, on the surface. These dots are probably due to current-carrying filaments.

SYNOPSISExperimental results on plasma treatments of polysulfone and polyetherimide to improve the wettability of these polymers are presented. The plasma is characterized by optical emission spectroscopy. The wettability of the polymer surfaces were checked by contact angle measurements and ESCA is used to compare the surfaces before and after plasma treatment. Correlations between contact angle, concentration of oxygen at the surface, and optical emission intensity of the OH radical have been established. Optimization of operational plasma parameters leading to the best wettability of the treated samples is reported. I NTRO D U CTlO NIn many technical applications, the desired surface and volume properties are not the same. Hence, it becomes difficult for a single material to fit both surface and volume requirements. At least for this reason, surface treatment and surface modification of polymeric materials is a domain of growing interest. Purely chemical, ' purely physical, and combined physical and ~h e m i c a l~'~ processes have been used to modify the surface of a polymer. In the last group, plasma techniques seem to be very powerful because it is a low-temperature treatment, applicable to a large variety of materials, and able to change the surface properties to a large extent (e.g., from wettability to impermeabilisation ) . 5 The main drawbacks of this technique are:1. The transfer from a small experimental setup to a large reactor fitting the real size and geometry of the items considered is not a simple homothetie. 2. A good understanding of the interactions between plasma species and treated surfaces, necessary to have a good control on the plasma parameters, is often very difficult to achieve.This article deals with the latter aspect. It is an attempt to establish relationships between three sets of parameters: ( 1 ) macroscopic parameters of the plasma (pressure, power, geometrical parameters) ; ( 2 ) composition of the gas phase with particular attention to the species responsible for surface modifications; and ( 3 ) composition and properties of the surface after plasma treatments.The first set of parameters is experimentally fixed during the plasma treatment. The plasma gas phase composition was checked by optical emission spectroscopy; the changes in surface composition were controlled by ESCA measurements. The surface wettability was evaluated by contact angle method, while the hydrophilic properties were determined by Hamilton's method.6From a technological point of view, the aim of this work is to show how a plasma process has been optimized to give the best wettability of two polymers-polysulfone ( PS ) and polyetherimide (PEI) -which are of great interest to make ultrafiltration and microfiltration membranes. Of course, in this case, wettability is one of the most important surface properties for these polymers.