Controlled sub-10-nanometer poly(N-isopropyl-acrylamide) layers grafted from silicon by atom transfer radical polymerization

Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to graft poly(N-isopropylacrylamide) (PNIPAM) brush layers with a controllable thickness in the 10-nm range from silicon substrates. The rate of polymerization of N-isopropylacrylamide was tuned by the [Cu(II)]₀/[Cu(I)]₀ ratio between the deactivating and activating species. The polymer layer thickness was characterized by atomic force microscopy (AFM) and ellipsometry. PNIPAM layers with a dry thickness between 5.5 and 16 nm were obtained. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed that the chemical structure is PNIPAM brushes. Analysis of the AFM data showed that our procedure leads to polymer grafts in the "mushroom-to-brush" transition regime.