Plasma Polymers Of Trimethylsilane Research Articles

Adhesion of spray primers to plasma polymer coatings

AbstractThe adhesion failure of a primer on a plasma‐polymer‐deposited substrate surface could occur at the interface of the substrate/plasma polymer or at the interface of the plasma polymer/primer. We examined the adhesion of spray (solventborne or waterborne) primers on plasma polymer coated substrate with the substrate/plasma polymer systems in which the adhesion of the plasma polymer of trimethylsilane (TMS) to the substrate was good. Waterborne primers adhered well to quite hydrophobic plasma polymer surfaces, except the untreated surface of TMS. The plasma polymer of TMS appeared to contain a significant amount of oligomers, which were not in the three‐dimensional network of the plasma polymer coating and caused poor adhesion of primers. The plasma treatment of the deposited plasma polymer of TMS increased the adhesion characteristics of the primers dramatically. The oxygen‐plasma treatment, however, made the interface water sensitive and made the wet adhesion poor. The argon‐plasma treatment of the plasma polymer of TMS was found to be a viable process that yielded excellent adhesion of spray primers. The plasma polymer of TMS deposited by a closed system, without further plasma treatment, yielded an excellent foundation for the application of spray primers. Waterborne, nonchromated primers adhered exceedingly well and survived 8 h of boiling in water (with a scribed surface) and became virtually nonstrippable by conventional stripping agents. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1443–1457, 2002

Adhesion of the plasma polymer of trimethylsilane to aluminum alloys

AbstractThe adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrates depends on the cleanliness of the substrate surface and the state of oxides on the aluminum alloy surface. Both factors are dependent on what type of alloy is used, and consequently, the best preparation of the substrate surface differs on the type of aluminum alloy. Oxygen plasma treatment is effective for the elimination of organic surface contamination, but plasma treatment, such as that of mixed argon and hydrogen, cannot be used to modify the surface state of oxides on these alloys. This is because oxides of aluminum are stable and thus resist plasma modification, and prolonged plasma treatment has been observed to change concentrations of alloy components at the surface due to the heating of the alloy. Chemical cleaning of the surface is necessary before the application of the plasma polymer used for corrosion protection enhancement. Once the surface was properly prepared, a plasma polymer of trimethylsilane (TMS), prepared by cathodic polymerization, adhered well to aluminum alloys investigated in this study. Major adhesive failure, however, occurred as a consequence of reactor contamination when hexafluoroethane (HFE) plasma treatment of initially formed TMS plasma polymers was employed. Plasma pretreatment of the substrate with O2 or postplasma treatment of the plasma polymer of TMS with Ar (instead of HFE) was effective in eliminating the surface‐contamination effect on the adhesion. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1387–1398, 2002

ESR Study of Trimethylsilane Plasma Polymer Part II; Effect of Consecutive Treatments and Mixed Gases

An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethylsilane (TMS) monomer gas has the ability to modify the characteristics of the primary plasma polymer significantly in a favorable manner for many applications. The effect of the second plasma polymerization on the primary plasma polymer of TMS depends on the nature of the second monomer. Plasma of F-containing monomer, hexafluoroethane (HFE) and perfluoromethane (CF4), decreases the ESR signal of TMS and no detectable signal due to F-containing monomer was found. The decay rate of the signal decreased significantly. In contrast to this situation, CH4 plasma treatment yields an ESR signal that is a composite of that observed from TMS and CH4 films individually. The overall signal increased in this instance, but didn't show appreciable decay in 24 hr period. A second treatment by nonpolymer forming plasmas also decreased the ESR signal of TMS, and decreased the decay rate, indicating that the second gas plasma treatment yields a somewhat similar effect found with the HFE plasma treatment. Plasma polymerization of mixtures of TMS and nonpolymer-forming gases increased the ESR signal but decreased the decay rate, except in the case of oxygen. A mixture of (TMS + O2) behaved as a completely different monomer. No ESR signal was found in this system. The ESR analysis was supported by XPS data and an insight into the mechanisms occurring in these thin films are discussed.

Static and Dynamic Contact Angles of Water on Polymeric Surfaces

Static contact angle and dynamic (advancing and receding) contact angles of water on polymeric surfaces were investigated using microscope cover glasses coated with various plasma polymers of trimethylsilane and oxygen. By variation of the mole fraction of the TMS/oxygen mixture, glass surfaces having varying degrees of wettability were prepared. The advancing contact angle of a sessile droplet, which is independent of the droplet volume, is considered as the static contact angle of water on a polymeric surface, θS, which is a parameter characteristic to a polymeric surface. The dynamic contact angle of water refers to the contact angle of which three-phase contact line is in motion with respect to the surface. The dynamic advancing (immersing) contact angle, θD,a, and receding (emerging) contact angle, θD,r, were measured by the Wilhelmy balance. The difference between θD,a and θD,r is mainly due to the direction of dynamic force acting on the three-phase contact line. The discrepancy between the immersion and the emersion buoyancy lines and the corresponding values of contact angles can be used to indicate the hysteresis due to the dynamic factor (the dynamic hysteresis). The dynamic hysteresis is largely determined by the critical immersion depth in which the three-phase contact line remains at the same place on the surface while the shape of meniscus changes when the motion of the sample is reversed. The dynamic hysteresis may contain the contribution of the change of static contact angle due to the surface-configuration change caused by the wetting of the surface (the intrinsic hysteresis). The dynamic hysteresis varies according to the value of cos θS, with the maximum at the threshold value around 0.6 and linearly decreases above this value, as the emersion line approaches the limiting buoyancy line determined by the surface tension of the liquid. The intrinsic hysteresis follows the same trend with the maximum at around 0.8. The three contact angles are related by cos θS = (cos θD,a + cos θD,r)/2.

Corrosion protection of cold-rolled steel by low temperature plasma interface engineering II. Effects of oxides on corrosion performance of E-coated steels

The effects of oxides on the interfacial chemistry and on the corrosion performance of cathodic E-coat/cathodic plasma polymer of trimethylsilane (TMS)/cathodic plasma treated cold-rolled steel (CRS) systems were investigated. The depth profile analysis by sputtered neutral mass spectroscopy (SNMS) revealed that the nature of the chemical bonds in the plasma polymer/steel interface depends on the presence or the absence of oxides. The cathodic plasma treatment of CRS surface by (Ar + H 2) plasma removes oxides, and the subsequent in situ cathodic polymerization of TMS provides the plasma polymer of TMS/(oxide-free) steel system, in which Fe-C bonds, but no Fe-O bond, are found. The deposition of the same plasma polymer on O 2 plasma pretreated CRS provides the plasma polymer/oxides/steel system, in which Fe-O, but no Fe-C, bonds are found. During the cathodic E-coat deposition, the reducible moieties which exist in the surface state of CRS (including plasma polymer layer and oxides, etc.) are subjected to cathodic reduction. The cathodic reduction could create a weak boundary or defective spots in the interface, which adversely affect the corrosion protecting ability of the coated system. The cathodic E-coat applied directly on the oxide-removed surface of CRS (without Zn phosphate or plasma polymer) showed a better corrosion performance than that applied on the Zn phosphate-chromate CRS, whereas the direct application on the surface with oxides delaminated in the corrosion (GM scab) test. The best result (better than E-coat/Zn phosphate-chromate/EGS) was obtained for E-coat/cathodic polymer of TMS/oxide-free CRS. The corrosion performance of this system was not adversely affected when lead was removed from the E-coat. A cathodic E-coat performs best when the adverse effect of cathodic reduction is minimized.

Corrosion protection of cold-rolled steel by low temperature plasma interface engineering: I. Enhancement of E-coat adhesion

An anode magnetron enhanced d.c. cathodic plasma treatment of a cold-rolled steel (CRS) plate and cathodic (plasma) polymerization were used to create interface engineered systems of cathodic E-coat/plasma polymer/plasma treated CRS. The adhesion of the E-coat and the corrosion protection characteristics of the systems were compared with the control, E-coat/Zn phosphate-chromate/alectro-galvanized steel (EGS). The adhesion of the E-coat to the plasma polymer coaled CRS was found to be excellent; the E-coat could not be removed by N-methyl pyrrolidone (60 °C) in 5 days, while the same E-coat applied on the control was removed in a few minutes. The plasma polymer of trimethylsilane (TMS) was found to yield excellent corrosion protection as used in the interface engineered systems, of which the corrosion (GM scab) test was found to be better than that for the control. The plasma pretreatment of the CRS surface prior to the cathodic polymerization of TMS was found to be a critically important factor. The corrosion-induced delamination of the first paint layer seems to play a key role in the corrosion of painted steel. It was demonstrated that good adhesion and durability of the entire interface system can produce a highly corrosion resistant painted CRS.

Modification of wettability of a stainless‐steel plate by cathodic plasma polymerization of trimethylsilane–oxygen mixtures

AbstractWettability (by water) of a stainless‐steel plate was modified by depositing an ultrathin layer of a plasma polymer of trimethylsilane (TMS) and an oxygen mixture. Plasma polymerization was carried out by cathodic glow discharge polymerization, in which a substrate stainless‐steel plate was used as the cathode of the de glow discharge. The plasma polymer of TMS (oxygen mol fraction = 0) is very hydrophobic, but the addition of oxygen in the monomer mixture increased the hydrophilicity of the plasma polymer. The value of cos θ (θ: advancing contact angle of water) linearly increased with the mol fraction of oxygen in the monomer mixture. Oxygen in the monomer mixture acts as (1) an ablating agent of a carbon‐based plasma polymer and (2) a comonomer for a silicon‐based plasma polymer. The atomic composition of a plasma polymer, which can be expressed as SiCxOy, changes (x decreases and y increases) as the mol fraction of oxygen increases. © 1995 John Wiley & Sons, Inc.