Chemical Bonds to the Resulting Adhesion Strength

CH2 (ethylene-like) groups did not show any interaction with electron-beam evaporated aluminum - the peel strength is zero. Therefore, it was concluded that any chemical and physical interactions were absent. In the literature, contradictory results were obtained by considering the interactions between freshly evaporated Al atoms and aliphatic chains in polyethylene and polypropylene in more detail. The proposed formation of Al-C bonds did not influence the adhesion strength [30, 31] and could not be confirmed in other experiments [85, 86]. These Al-C bonds are unstable toward hydrolysis, and thus they should not contribute significantly to the peel strength [24]. 

One can argue that aliphatic plasma polymers from ethylene or propylene produced in the continuous-wave mode have significant structural anomalies in comparison with the respective classical products [24] and therefore they should increase the adhesion strength rather than keeping it at a constant (low) level. As seen in this work, the structural anomalies of aliphatic layers were minimized by the use of the pulsed plasma technique. This is demonstrated by the 

COOH groups interact strongly with metallic Al with the result that all the carboxylic groups are consumed [85]. It is the same situation as with OH groups. First, Al reacts with the acidic groups with the formation of salt-like structures [Eq. (C)]. 

Moreover, A1 can also form weak interactions with COOH groups this happens preferentially to the C=0 site first, thus forming A- C-O interactions [88] but there follows the formation of (weak) interactions to the C-O site [46]. The end product of the Al-COOH reaction is AI2O3. Its formation can be considered as a redox reaction again [40, 84] because of the reduction of C=0 and C-O sites and the oxidation of Al. In this case, unspecific thermodynamic adhesion must be impHed. The exact experimental proof of all the interactions and bond formation discussed here is matter for future work. 

Dependence of Adhesion Strength on Concentration of Functional Croups at the Polymer S 

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