Bioinspired Adhesion Polymers: Wear Resistance of Adsorption Layers

Abstract

Mussel adhesive polymers owe their ability to strongly bind to a large variety of surfaces under water to their high content of 3,4-di­hydroxy-l-phenyl­alanine (DOPA) groups and high positive charge. In this work, we use a set of statistical copolymers that contain medium-length poly­(ethylene oxide) side chains that are anchored to the surface in three different ways: by means of (i) electrostatic forces, (ii) catechol groups (as in DOPA), and (iii) the combination of electrostatic forces and catechol groups. A nanotribological scanning probe method was utilized to evaluate the wear resistance of the formed layers as a function of normal load. It was found that the combined measurement of surface topography and stiffness provided an accurate assessment of the wear resistance of such thin layers. In particular, surface stiffness maps allowed us to identify the initiation of wear before a clear topographical wear scar was developed. Our data demonstrate that the molecular and abrasive wear resistance on silica surfaces depends on the anchoring mode and follows the order catechol groups combined with electrostatic forces > catechol groups alone > electrostatic forces alone. The devised methodology should be generally applicable for evaluating wear resistance or “robustness” of thin adsorbed layers on a variety of surfaces.

Nanoscale Wear and Mechanical Properties of Calcite: Effects of Stearic Acid Modification and Water Vapor

“…Interestingly, two characteristic stick-slip lengths have been reported for adsorbed catechol-containing polymers, whereas adsorbed polyelectrolytes without catechol groups displayed one single characteristic stick-slip length. 28 …”

“…This is similar to that observed for bare calcite, but unlike what has been previously observed for polymer layers that deform plastically, − there is no clear characteristic stick-slip length. Interestingly, two characteristic stick-slip lengths have been reported for adsorbed catechol-containing polymers, whereas adsorbed polyelectrolytes without catechol groups displayed one single characteristic stick-slip length …”

“…Interestingly, two characteristic stick-slip lengths have been reported for adsorbed catechol-containing polymers, whereas adsorbed polyelectrolytes without catechol groups displayed one single characteristic stick-slip length. 28 Patchy Stearic Acid Layer. In this section, we consider the situation with an incomplete and patchy stearic acid layer that is formed during short time exposure (10 min) to stearic acid vapor at 105 °C, where the initial water contact angle was found to be ∼70°.…”

“…The local wear resistance of adsorbed fatty acid layers on calcite, and how it is affected by the environment, has not been clarified. So far, in particular, the initiation of wear on a local scale on modified calcite surfaces has not been considered in detail, although the atomic force microscopy (AFM)-based method itself for assessing local wear has been used for other organic systems and is considered as well suited. , To this end, we prepared and characterized unmodified and stearic acid surface-modified rhombohedral CaCO 3 mineral surfaces using stearic acid vapor exposure. Both fully covered surfaces and surfaces coated with a patchy stearic acid layer were considered.…”

Synthesis and Properties of Cationic Gradient Brush Copolymers Carrying PEO Side Chains and Catechol Moieties

“…It was demonstrated in our previous paper [ 36 ] that neutral catechol brush copolymers are relatively stable in acidic aqueous solutions but unstable in neutral and alkaline solutions undergoing coloring because of oxidation reactions involving catechol groups. It was also demonstrated [ 48 ] that underwater wear resistance of the adsorbed layers of cationic catechol brush copolymers is exclusively high and significantly exceeds that of uncharged catechol brush copolymers. In the above context, it was important to evaluate stability against oxidation of the cationic catechol brush copolymers and compare it with the stability of catechol bush copolymers of similar structure but do not carry charge.…”