Wetting of Surface Grafted Hydrophilic-b-Hydrophobic Block Copolymer Brushes

The wetting of diblock copolymer brushes by water is studied. Th goal of this work is to understand how the thickness of the bottom and top copolymer block affect the wetting behavior, respectively. For the synthesis of diblock copolymer brushes the bottom block, a hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) brush is grafted from a undecyl-trichloro-self- assembled monolayer on silicon wafer. Then the top block, a hydrophobic polystyrene (PS) or poly(2-ethylhexyl methacrylate) (PEtHexMA) is grafted from the PHEMA block. Hereby, a hydrophilic-b-hydrophobic diblock copolymer is obtained. The top copolymer block determines the advancing contact angle of the copolymer brushes in their pristine state. The receding contact angle depends on the thickness of the top and bottom copolymer block. For a top copolymer thickness <30 nm the receding contact angle decreased. An increase in the thickness of the bottom block to 35 nm decreases the receding contact angle as well. By exposing the diblock copolymer brush with a thickness of the top block >30 nm to warm water the wetting properties switch from a hydrophobic to a hydrophilic. The surface switches back to the hydrophobic state by exposing it to toluene and subsequent temperature annealing.