General Aspects of the Chemistry and Physics of Polymer Brushes

The term "polymer brush" was coined by deGennes to describe an architecture in which polymer chains are terminally tethered to a surface at a very high denisty (= anchoring density is much smaller than coil dimensions). Due to this overcrowding the chains stretch perpendicular to the surface until the loss of possible conformations (loss in entropy) balances the enthalpic gain of segment dilution. The situation is illustrated in the image to the right in a somewhat simplified way as the chains are drawn invidually as if there would be no overlap.

The best way to realize such an architecture is to grow the chains directly at the surface of the substrate. This approach - called "grafting from" - is schematically shown in the image to the left. In a first step, the surface is decorated with an monolayer of an initiator (the green balls) which can then be used to "grow a lawn" of polymer molecules. Using this approach we are able to create monolayers of a variety of polymers with thickness between a few nanometers and a few micrometers. The properties of the layers can be readily adjusted by choosing an appropriate monomer. If needed, a fine-tuning of the properties can by realized by using monomer mixtures to create monolayers of copolymers.