A stable adhesion of polymer coatings is crucial for many applications. Using non-covalent interaction could be superior to covalent bonds as they can reform after breakage. Here, we utilize an atomic force microscopy based method to resolve how the presence of side chains and their molecular architecture influences the adhesion and the mobility of polymers on solid substrates. Surprisingly, for non-covalently bound polymers that are mobile in the plane of the surface, we could show that the adhesion is unaffected by the addition of side chains and their architecture. For less mobile polymers, a significant increase in adhesion force upon the addition of side chains was observed. This could be explained by a combinational effect of entanglements and contact area. The findings have been deduced from natural and synthetic polypeptides and also from graft, bottle-brush and branched ones. They should help designing polymers for stable non-covalent surface coatings.
Figure Legend: “Scheme of an AFM cantilever with a single polymer covalently attached to its tip. The adhesion of various polymer architectures on solid substrates is investigated. Various polymer architectures are schematically depicted on the right.”
Langmuir, 2014, 30 (15), pp 4351–4357.
Sandra Kienle †, Markus Gallei ‡, Hao Yu §,Baozhong Zhang §, Stefanie Krysiak †, Bizan N. Balzer †, Matthias Rehahn ‡, A. Dieter Schlüter §, and Thorsten Hugel *†
† Physik Department E22 and IMETUM, Technische Universität München, 85748 Garching, Germany and
‡ Ernst-Berl Institut für Makromolekulare Chemie, TU Darmstadt, Alarich-Weiss-Str. 4, 64287 Darmstadt,Germany and
§ Department of Materials,ETH Zurich, Vladimir Prelog Weg 5, HCI J 541, Zurich, Switzerland.
Several applications require strong noncovalent adhesion of polymers to substrates. Graft and branched polymers have proven superior to linear polymers, but the molecular mechanism is still unclear. Here, this question is addressed on the single molecule level with an atomic force microscopy (AFM) based method. It is determined how the presence of side chains and their molecular architecture influence the adhesion and the mobility of polymers on solid substrates. Surprisingly, the adhesion of mobile polymers cannot significantly be improved by side chains or their architecture. Only for immobile polymers a significantly higher maximum rupture force for graft, bottle-brush, and branched polymers compared to linear chains is measured. Our results suggest that a combination of polymer architecture and strong molecular bonds is necessary to increase the polymer–surface contact area. An increased contact area together with intrachain cohesion (e.g., by entanglements) leads to improved polymer adhesion. These findings may prove useful for the design of stable polymer coatings.
Copyright © 2014 American Chemical Society.