Entropic interactions: neutral and end-functionalized chains in confined geometries

摘要

The abrupt liquid-to-solid transition experienced by simple non-polar Liquids with quasi-spherical molecules when compressed to a few molecular layers between smooth, solid surfaces can be drastically modified by the presence of polymeric chains end-attached to the surfaces (polymer brushes). The origin of this is the weak interpenetration of the brushes, which can be strongly compressed and yet have a very fluid interfacial region when sheared past each other, resulting in very low friction. The use of telechelic brushes, which are functionalized at both ends and could form loops rather than tails, should result in an even lower interpenetration, and thus in a better lubrication effect. A simple calculation, however, shows that brush-like dimer or multimer-structures might be more favourable energetically than simple loops in the case where the telechelic end-groups attract each other, leading to a very different form of interactions. Recent measurements of the normal and shear forces between surfaces bearing layers of telechelic brushes are in line with these expectations. [References: 29]