Silver metal/polymer interfaces

The study of LB films by ESCA and SIMS provides some important lessons for the metal polymer interface. The surface chemistry of polycrystalline silver is active enough to effect the protonation process to form molecular ions. Yet, the chemistry is not sufficient to completely deprotonate the fatty acids and produce carboxylate salts with the silver as counter ion. The... 

In contrast, in most ion-selective membranes the charge conduction is done by ions. Thus, a mismatch between the charge-transfer carriers can exist at the noble metal/membrane interface. This is particularly true for polymer-based membranes, which are invariably ionic conductors. On the other hand, solid-state membranes that exhibit mixed ionic and electronic conductivity such as chalcogenide glasses, perovskites, and silver halides and conducting polymers (Lewenstam and Hulanicky, 1990) form good contact with noble metals. 

Metal-polymer fractal interfaces may result from processes such as vacuum deposition and chemical vapor deposition where metal atoms can diffuse considerable distances into the polymer. Mazur et al. [76,77] electrodeposited silver within a polyimide film. The Silver [I] solution was able to diffuse into the polymer film where it... 

Fig. 3. The ramified fractal nature of diffuse interfaces is shown for (top) a computer simulated 2-d monomer-monomer interface where the heavy region represents the connected monomers on one side, (middle) a simulated 2-d random coil polymer interface at the reptation time, and (bottom) electrochemically deposited Silver diffusing in polyimide with the unconnected metal atoms removed to show the fractal diffusion front of the connected metal atoms. (Wool and Long)...

The polymer-metal interface shown in Fig. was derived from an electron micrograph obtained by Mazur and Reich.They electrodeposited silver from a silver ion solution diffusing through a polyimide film. Particles not connected to the diffusion source were removed by computer analysis. The deposited silver particles essentially "decorate the concentration profile and permit the diffusion front to be observed. A 1000-A thin slice was used to aproximate two dimensional diffusion. The fractal dimension of this interface was determined by computer analysis to be approximately 1.7. Similar ramified interface fronts are created by vapor deposition of metal atoms on polymers and by certain ion bombardment treatments of polymer surfaces. The fractal front is fairly insensitive to the details of the concentration profile. However, strong chemical potential gradients in asymmetric interfaces may promote a more planar, less ramified structure. The fractal characteristics of polymer interfaces... 

As such exemplary experimental material, plasma polymer thin films with embedded silver particles are selected [3]. These films were made by simultaneous or alternating plasma polymerization and metal evaporation. The films can be deposited as multilayers consisting of two polymer thin films and a nanoparticle-containing film between these films. Because of the two plasma polymer layers on either side, the particles are completely embedded in a homogeneous media. The multilayer systems are very appropriate for determining particle size and investigating the interface between metal particles and plasma polymer matrix, because here metal nanoparticles are embedded in one plane. This allows a simple determination of the particle size and shape in the TEM. 

Conductive Adhesives. Electrically conductive adhesives are used today for specialized applications such as connections to LCD displays and attachment of small resistors and capacitors. These materials consist of conductive particles, usually silver flakes or carbon, suspended in a polymer matrix, most commonly epoxy.The electrical resistance of the contact to the PCB tends to be unstable over time, so these materials are not suitable for applications requiring a constant, low-resistance contact. The primary failure mechanism is moisture migration through the epoxy to the interface, resulting in oxidation of the contact metal. Adhesion strength is also a reliability concern. New materials suitable for a broader range of applications are under development. Further information can be found in Ref 39. 

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