Effect of molecular architecture on single polymer adhesion.

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.

Investigating single molecule adhesion by atomic force spectroscopy.

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

Measuring the interaction between ions, biopolymers and interfaces--one polymer at a time.

Atomic force microscopy (AFM) based single polymer force spectroscopy allows to detect the interaction (energy) between single polymers and interfaces in aqueous environment. We use this method to delineate the effect of ions, pH, co-solutes and temperature on the adhesion of biopolymers onto solid substrates.