Polystyrene-block-poly(acrylic acid) brushes grafted from silica surfaces: pH- and salt-dependent switching studies†
Abstract
We report the preparation, characterization and responsive behavior of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer brushes grafted from silica substrates using Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP). pH-dependent swelling behavior was investigated in situ by ellipsometry and it confirmed that PAA chains can be reversibly switched from collapsed to extended conformations. It also confirmed that the grafted copolymer brushes were stable under extreme alkaline conditions of pH and with added salt. We showed that the hydrophobic polystyrene block of the copolymer protects the substrate–initiator bond against hydrolysis that would otherwise cause undesired polymer degrafting from the substrate. Also, we provide evidence of fundamentally different brush conformations with metal cations of increasing valency. Monovalent sodium and cesium ions caused brush stretching while only collapsed brushes were observed with divalent calcium ions.