title: pH-Switchable Stratification of Colloidal Coatings: Surfaces "On Demand".
abstract: Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogeneous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratification when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and protective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition.
authors.affiliation: Department of Physics, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.|Department of Materials, Loughborough University , Loughborough, Leicestershire, LE11 3TU, United Kingdom.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Martín-Fabiani
authors.affiliation: Department of Physics, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Fortini
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1 , CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lesage de la Haye
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1 , CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France.
authors.forename: Ming Liang
authors.initials: ML
authors.lastname: Koh
authors.affiliation: Centre for Petroleum and Surface Chemistry, Department of Chemistry, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.
authors.forename: Spencer E
authors.initials: SE
authors.lastname: Taylor
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1 , CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France.
authors.forename: Elodie
authors.identifier: http://orcid.org/0000-0002-7049-3897
authors.initials: E
authors.lastname: Bourgeat-Lami
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1 , CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France.
authors.forename: Muriel
authors.initials: M
authors.lastname: Lansalot
authors.affiliation: Univ Lyon, Université Claude Bernard Lyon 1 , CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France.
authors.forename: Franck
authors.initials: F
authors.lastname: D'Agosto
authors.affiliation: Department of Physics, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Sear
authors.affiliation: Department of Physics, University of Surrey , Guildford, Surrey GU2 7XH, United Kingdom.
authors.forename: Joseph L
authors.identifier: http://orcid.org/0000-0001-9123-183X
authors.initials: JL
authors.lastname: Keddie
keywords: Brownian dynamics simulations; functional coatings; polymerization-induced self-assembly (PISA); stimuli-responsive; stratification