Bridging Attraction by Telechelic Polymers

Telechelic polymer chains, having a strongly adsorbing group on each end, can induce attractions between surfaces to which the end groups adsorb by forming “bridges” spanning the two surfaces. However, such chains may also adsorb on a single surface, forming a “brush” of stretched loops; this leads to repulsive interactions between surfaces, as the brushes resist compression and overlap. We show that bridging leads to a weak attractive minimum in the interaction energy between parallel surfaces of strength 1.0 × T(R/h)² per chain (where R is the free radius of a chain and h is the height of an isolated brush) for two brushes just in contact. We explore the consequences of this attraction for colloid stability, experiments using the surface forces apparatus, and telechelic chains in melt conditions including multiblock lamellar phases.