Y-shaped amphiphilic brushes with switchable micellar surface structures.

We observed novel nanoscale surface structures of segregated pinned micelles and craterlike micelles formed by grafted Y-shaped molecules and their reversible reorganization in selective solvents. The Y-shaped molecules have two incompatible polymer chains (polystyrene and poly(tert-butyl acrylate)) attached to a functional stemlike segment capable of covalent grafting to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity to the brush. We demonstrated that spatial constraints induced by a chemical junction of two relatively short (6-10 nm) dissimilar arms in such Y-shaped molecules lead to the formation of segregated micellar surface nanostructures in the grafted layer. We proposed a model of these segregated pinned micelles and the corresponding reverse micelles (craterlike structures) featuring different segregation states of hydrophobic polystyrene and hydrophilic poly(acrylic acid) arms. The arms undergo conformational rearrangements in selective solvents in a controlled and reversible fashion. These nanoscale structural reorganizations define adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure and switchable behavior can be considered as a promising way toward the patterning of solid substrates with adaptive nanowells, which could be used for trapping of adsorbing nanoscale objects.