Polymer brushes in restricted geometries

Abstract

The structure of polymer brushes has been the subject of considerable theoretical and experimental activity. Experimental measurements of the steric forces between grafted brushes and the structure of a single brush at the solid-solution interface are in good agreement with theoretical predictions. However, the physical structure brush layers adopt under confinement has remained elusive. Here, we report measurements of polymer brush density distributions in good solvent as a function of compression. The extension and interpenetration of the brushes are unambiguously determined using neutron reflectivity and contrast matching techniques. The measurements reveal a significant increase in brush concentration at the grafting surface with compression. This is in contrast to theoretical predictions of uniform density distributions as polymer brushes are compressed. The low interpenetration and brush compaction at the anchor surface provides new insight into why such layers are so effective at reducing friction and wear between surfaces.