Film Formation with Adhesion Promoters

The complete fihn has a duplex structure of a thin compact inner film and a porous outer part. This is important to understand the properties of these films. 

Electrochemical fihn formation is restricted to conducting materials. On inert metals a stable and adherent fihn may form. On corrosive metals like iron, oxidation of the metal prevents formation of a stable film. FUms on non-conducting materials can be formed by chemical oxidation but often suffer from insufficient adhesion. 

FUms on these materials can be formed if adhesion promoters are used. With adhesion promoters it is possible to deposit films of conducting polymers on insulators, semiconductors with highly polished surfaces, and corrosive metals. An adhesion promoter consists of an adhesion group, e.g., chloro- or hydroxy silane groups, phosphonic acid groups, which can bond to the surface of the soUd, spacer group, and a monomer molecule as a head group. 

For the preparation of a polymer film on a soUd, e.g., a silicon wafer, the solid is dipped into the solution of the adhesion promoter like chloroform for approximately Ih. The adhesion promoter can be expected to form a monomolecular fihn on the surface of the soUd. The structure of this monomolecular film is similar to that of a self-assembUng mono-layer (SAM). After rinsing the solid specimen is brought into a solution of the monomer 

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The interfacial term of friction is the main cause of adhesive wear and may involve processes such as stick-slip motion, transfer film formation with or without chemical bonding, chemical wear, fatigue wear, and thermal softening of the interface (2,24). The adhesive wear is promoted only when the roughness of the counterface is very low, a value where cohesive wear or ploughing due to counterface asperity interaction may be safely neglected, and the adhesive interaction between the polymer and the counterface as a result of junction growth becomes an important factor. 

For iron and steel parts, a different film preparation was developed that was based on adhesion promoters as described in Section 11.3. After formation of the SAM layer in a solution containing the adhesion promoter, the electrode was transferred into a cell filled with a solution of the monomer molecules and a supporting electrolyte. Then an anodic current pulse was applied for some seconds or minutes. A fihn of poly thiophene formed on the iron or steel parts with a thickness depending on the pulse time. Oxidation of the iron or steel was avoided by this procedure. The film had a compact structure, as was shown by SEM pictures. The adhesion promoter film provided exceUent protection against delaminating. 

An overview of the chemical methods employed to pretreat the polyetherimide is outlined in Figure 1. Removal of 0.5 )im of the polymer surface was accomplished via brief, 0.5 minute, contact with concentrated sulfuric acid. The subsequent water rinse resulted in the formation of a white film or residue. This layer could be removed either through solubilization or oxidation. Utilization of a solubilizer for the debris removal step also required a separate adhesion promotion step. The Standard 2312 process described previouslyS. 10,11 js solubilizer-free and depends on oxidation of the white residue to effect its removal. In this case, no separate adhesion promotion step is necessary and chemical modification of the polymer occurs in each of the principal pretreatment steps. ... 

Einally, linear amphiphilic PEG-Z)-PLLA-Z)-PLL triblock copolymers were synthesized and blended with PLLA for film formation. Investigation of the film surface revealed an enrichment of PLL blocks on the surface of the PLLA film. Human osteoblast tests performed on different PLLA films showed that the triblock copolymers were much more effective in promoting cell adhesion and proliferation compared to the PEG-6-PLLA diblock-modified and virgin PLLA films. The self-segregation of the PEG-6-PLLA-A-PLL triblock copolymers on the film surface demonstrated a potential application in the preparation of functional scaffolds for tissue engineering. 

Film Formation and Propoties.— Work on film preparation and subsequent processing of 2GT has been limited to studies on the transverse constriction and stresses observed during uniaxial orientation and the problems associated with the maintenance of planarity during heat relaxation. Orientation and shrinkage have been discussed in a number of papers with studies on orientational setf-ieinforcement and relaxation and its effects on orientation. The effect of the interaction of films with organic liquids has promoted studies on the structural arrangements in liquid-induced crystallization of cold-drawn 2GT films, and the effect of crystallization on adhesion and cohesion. ... 

Conducting polymers can be prepared by chemical or electrochemical techniques. Electrochemical synthesis provides easier routes when compared with chemical synthesis and allows control over film formation, especially relevant if polymers are required as thin films deposited on the surface of metallic substrates. However, electrochemically synthesized polymers are usually more porous, a feature that requires consideration when a barrier effect is necessary. Another important aspect in the corrosion field is that the application of potential/current necessary to promote electropolymerization may accelerate dissolution (corrosion) of the metal. In some cases, an oxide pre-layer is deposited between the metal and the polymer to promote adhesion and hinder metal dissolution during the electropolymerization process (Tallman et al., 2002 Spinks et al., 2002). Alternatively, the application of layered coatings based on different conducting polymers can be a strategy to overcome the problem of metal dissolution. In the work of Lacroix et al. (2000), a layer of PPy was firstly deposited on zinc and mild steel in neutral conditions, followed by deposition of PANi in an acidic medium, because the direct deposition of PANi on those metallic substrates was not possible in an acidic medium, causing dissolution of the metal. 

Most c. are - water-soluble polymers that produce aqueous systems with properties that promote adhesion, thickening, film-formation and defined rheology. 

The capability of plasmas to modify the chemical and physical properties of the surface without affecting the bulk properties of the base material has been advcinta-geous in several cases [35-38]. Either surface modification or thin film deposition can create specific surface chemistries for optimization of membrane performances in separation processes [39]. It is well known that the surface wettabihty and the adhesion of polymer can be significantly improved by plasma treatment with non-polymer-forming gases. The plasma treatment also leads to the formation of radicals [35] that are promoters of surface cross-linking functionahzation. 

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