title: pH- and Electro-Responsive Properties of Poly(acrylic acid) and Poly(acrylic acid)-block-poly(acrylic acid-grad-styrene) Brushes Studied by Quartz Crystal Microbalance with Dissipation Monitoring.
abstract: We report on the synthesis of novel pH- and electro-responsive polyelectrolyte brushes from a gold substrate by direct one-step nitroxide-mediated polymerization of acrylic acid (AA) or copolymerization of AA and styrene (S). In the latter case, amphiphilic brushes of block-gradient copolymers PAA-b-(PAA-grad-PS) comprising one PAA block and one block with the gradient sequence of AA and S were obtained. The block-gradient copolymers are initiated from the surface by the start of the PAA block. The brushes were characterized by XPS and ellipsometry. (1)H NMR confirmed the gradient sequence of the PAA-grad-PS copolymer block. The pH- and electro-responsive properties of the brushes were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) in combination with electrochemistry. This method provides evidence of swelling of the PAA brushes proportional to the contour length of the chains at elevated pH, whereas the response functions of the block-gradient copolymers are more complex and point to intermolecular aggregation in the brush at low pH. Monitoring of the changes in resonance frequency and dissipation of the QCM-D also demonstrates that application of negative voltage to the substrate leads to swelling of the brush; application of a positive voltage provokes only a transient collapse of the brush in proportion to the applied voltage.
authors.affiliation: ‡Department of Polymer Science, Moscow State University, Leninskie Gory, Moscow 119191, Russia.
authors.forename: O V
authors.initials: OV
authors.lastname: Borisova
authors.forename: L
authors.initials: L
authors.lastname: Billon
authors.affiliation: §CICbiomaGUNE, 20009 Donostia-San Sebastian, Spain.|∥Université Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France.|⊥Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany.
authors.forename: R P
authors.initials: RP
authors.lastname: Richter
authors.affiliation: #Department of Nanobiotechnology, Institute for Biologically Inspired Materials, University of Natural Resources and Life Sciences Vienna, A-1190 Vienna, Austria.
authors.forename: E
authors.initials: E
authors.lastname: Reimhult
authors.affiliation: ∇Mechanics and Optics, St. Petersburg National Research University of Information Technologies, 197101 St. Petersburg, Russia.
authors.forename: O V
authors.initials: OV
authors.lastname: Borisov
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D000180:Acrylic Resins / Q000737:chemistry*; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D011137:Polystyrenes / Q000737:chemistry*; D058525:Quartz Crystal Microbalance Techniques
chemical_list: D000179:Acrylates; D000180:Acrylic Resins; D011137:Polystyrenes; C509855:poly(styrene-b-acrylic acid); C006903:carbopol 940