Tuning Surface Mechanical Properties by Amplified Polyelectrolyte Self-Assembly: Where "Grafting-from" Meets "Grafting-to"

We report the interaction of surface-tethered weak polyacid brushes, poly(methacrylic acid), with a weak polybase poly(L-lysine)-graft-poly(ethylene glycol), in solution. The grafted polyacid brushes, grown directly from the silicon substrate by UVLED surface-initiated polymerization, act as a nanotemplate for the solution-phase polybase, which penetrates into the brushes, forming a polyelectrolyte complex (PEG), whose mechanical and nanotribological properties are markedly influenced by the electrostatic assembly conditions. The mechanical effects are amplified due to the architecture of the specific polybase used, which contributes approximately 2k Da per unit charge to the overall system, resulting in an efficient filling of the polyacid brushes, which thus acts as a scaffold. The distribution of the adsorbed copolymers in the PEC films has been investigated by means of confocal microscopy. The unique structure of the PEG films provides a system whose mechanical and nanotribological properties can be tuned over a wide range.