Layers metal/polymer interfaces

Friedrich et al. also used XPS to investigate the mechanisms responsible for adhesion between evaporated metal films and polymer substrates [28]. They suggested that the products formed at the metal/polymer interface were determined by redox reactions occurring between the metal and polymer. In particular, it was shown that carbonyl groups in polymers could react with chromium. Thus, a layer of chromium that was 0.4 nm in thickness decreased the carbonyl content on the surface of polyethylene terephthalate (PET) or polymethylmethacrylate (PMMA) by about 8% but decreased the carbonyl content on the surface of polycarbonate (PC) by 77%. The C(ls) and 0(ls) spectra of PC before and after evaporation of chromium onto the surface are shown in Fig. 22. Before evaporation of chromium, the C(ls) spectra consisted of two components near 284.6 eV that were assigned to carbon atoms in the benzene rings and in the methyl groups. Two additional... 

Metal thin films deposited on polymers are widely used in various industrial domains such as microelectronics (capacitors), magnetic recording, packaging, etc. Despite much attention that has been paid in the recent literature on the adhesive properties of metals films on polyimide (PI)( 1 - 5 ) and polyethyleneterephtalate (PET)((L) it appears that a better knowledge of the metal/polymer interface is needed. In this paper we focus ourself on the relationship between the adhesion and the structural properties of the aluminum films evaporated (or sputtered) on commercial bi-axially stretched PET (Du Pont de Nemours (Luxembourg) S.A.). A variety of treatment (corona, fluorine,etc.) have been applied in order to improve the adhesion of the metallic layer to the polymer. The crystallographic... 

As will be shown later, during cathodic delamination of a polymer from a metal surface due to ingress of an electrolyte into the metal/polymer interface, an additional liquid phase could be formed between the substrate and the organic layer. In this case, the metal/electrolyte interface can be treated as a conventional electrochemical interface, but an additional Galvani potential difference ADonnan potential or membrane potential [24—26]) has to be taken into account at the electrolyte/polymer interface. The latter is directly correlated with the incorporation of ions into the polymer membrane according to Eq. (14). 

Oxygen reduction takes place in the defect with a rate that is controlled by the transport of oxygen through the electrolyte layer (a, i). Thus, a galvanic current is established between the anodic site (zinc within the delaminated zone) and the defect (cathode). In the area between the two potential steps (b, ii), no equilibrium potential surface is observed but the potential rises continuously from the borderline of the local anode to the potential jump, which indicates the intact metal-polymer interface. It can be assumed that the closer the zinc to the cathodic delamination front the smaller is the local anodic current while the... 

Conversion layers lead to an increased adhesion strength of organic coatings on metals xmder dry and wet conditions. In addition, the kinetics of ion and electron transfer processes at the metal-polymer interface are slowed down. In case of iron and zinc, especially the oxygen reduction rate, which strongly influences the delamination kinetics of the coating, is reduced. 

It is possible to measure the work function of metal, electrolyte, or polymer surfaces only sufficient conductivity for currents in the order of 10 A is required. Furthermore, as already mentioned, the work function at the surface of a thin layer of electrolyte or polymeric coating and the electrode potential at the metal/electrolyte or metal/polymer interface beneath it are linearly related [99]. Once the calibration curves are known, it is possible to measure through the coating and obtain information about the electrochemical conditions at the interface without destroying it. For more details, see other references [110]. 

Another theory claims that a protective complex between the metal and the CP is formed in the metal-polymer interface. Kinlen et al. [73] found by electron spectroscopy chemical analysis (ESCA) that an iron-PANl complex in the intermediate layer between the steel surface and the polymer coating is formed. By isolating the complex, it was found that the complex has an oxidation potential 250 mV more positive than PANI. According to Kinlen et al. [73], this complex more readily reduces oxygen and produces a more efficient electrocatalyst. 

The development of an adequate equivalent circuit has been controversially discussed in the literature. Gabrielli et al. considered the polymer primarily as a non-porous layer. Transport processes in the polymer matrix dominated the impedance. Vorotyntsev et al. developed a model that took into account the electron transfer at the metal—polymer interface, transport of charge carriers in the film, and ion transfer at the polymer-electrolyte interface (Figure 11.16). 

In experiments covering a larger potential region, from the oxidized state until the complete neutral state, a new resonance circuit was found not described by the transmission line model. A new model was suggested by Pickup et al., which was used and modified later by Rammelt and Plieth et This model is corroborated by the duplex film structure (Figure 11.9). A compact layer on the metal/polymer interface with neutral state properties in the neutral state and double-layer properties in the oxidized state describes the compact polymer film the transmission fine model represents the porous part (Figure 11.17). 

In the present paper. Static Secondary Ion Mass Spectrometry (SSIMS) is used to investigate the interfacial chemistry between vacuum-deposited Al and Cu on PET by following the initial stages of metallization in the submonolayer and monolayer regimes. From the SIMS intensity variations with the deposited metal flux, information on the initial growth mechanisms of the metal layer Is expected. Two metals, copper and aluminum, have been chosen In order to investigate the influence of the metal reactivity on the metal-polymer interface formation. Aluminum with its electropositive sp band is known to react strongly with the carbonyl functionalities of the whereas copper is an inert metal and its Interaction is believed to be much weaker. ... 

Additional evidence of oxygen being involved as pait of the metal polymer link was obtained by examining the thiclmess of the metal oxide layer on the outer surface of the metal and at the metal/polymer interface prior to and subsequent to the heat-tieatment step. Analysis of the backside of the intetphase region was accomplished via dissolution of the polymer substrate The data in Table VI show that the oxide thicknesses were nominally equal at the air and polymer sides of the structure. The oxide thicknesses were independent of metal deposition technique although the presence of the palladium catalyst employed for electroless deposition complicated the analyses. X-ray photoelectron spectroscopy identified the oxide species as cuprous oxide 10,17. Excellent adhesion was obtained once the oxide thickness exceeded 3 nm at the metal/polyetherimide interfacial zone. 

Two charge-transfer semicircles are expected, which correspond to two RC parallel combinations of the doublelayer capacitance and charge-transfer resistance at the electrode-polymer interface and the double-layer capacitance and charge-transfer resistance at the polymer-electrolyte interface. At the metal-polymer interface, electron transfer would occur while at the polymer-electrolyte interface anion transfer is expected. 

However, it is important to pay attention to more than just the electronic charging of the polymer film (i.e., to electron exchange at the metal polymer interface and electron transport through the smface layer), since ions will cross the film solution interface in order to preserve electroneutrality within the film. The movement of counterions (or less frequently that of co-ions) may also be the ratedetermining step. 

Fig. 6.1 A schematic picture of a polymer film electrode. In an electrochemical experiment the electron transfer occurs at the metal polymer interface that initiates the electron propagation through the film via an electron exchange reaction between redox couples A and B or electronic conduction through the polymer backbone. (When the polymer reacts with an oxidant or reductant added to the solution, the electron transfer starts at the polymerjsolution interface.) Ion-exchange processes take place at the polymer solution interface in the simplest case counterions enter the film and compensate for the excess charge of the polymer. Neutral (solvent) molecules (O) may also be incorporated into the film (resulting in swelling) or may leave the polymer layer...

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