title: Electrostatic Swelling Transitions in Surface-Bound Microgels.
abstract: Herein, electrostatic swelling transitions of poly(ethyl acrylate-co-methacrylic acid) microgels covalently bound to silica surfaces are investigated. Confined at a solid surface, microgel swelling is anisotropically hindered and the structure is flattened to an extent dictated by pH and microgel composition. Microgel deformation under applied load is also shown to depend on microgel charge density, with the highest deformation observed at intermediate charge densities. Two modes of microgel deformation under load were observed, one elastic and one viscoelastic, related to polymer strand deformation and displacement of trapped water, respectively. Results on polymer strand dynamics reveal that the microgels are highly dynamic, as the number of strand-tip interaction points increases 4-fold during a 10 s contact time. Furthermore, finite element modeling captures these effects qualitatively and shows that stress propagation in the microgel network decays locally at the rim of contact with a solid interface or close to the tip probe. Taken together, the results demonstrate a delicate interplay between the surface and microgel which determines the structure and nanomechanical properties of the latter and needs to be controlled in applications of systems such as pH-responsive surface coatings in biomaterials.
authors.affiliation: Department of Pharmacy, Uppsala University , P.O. Box 580, SE-752 32 Uppsala, Sweden.
authors.forename: Lina
authors.initials: L
authors.lastname: Nyström
authors.affiliation: Department of Surface and Corrosion Science, School of Chemical Science and Engineering, KTH Royal Institute of Technology , SE-100 44 Stockholm, Sweden.|Institute for Advanced Studies, IMDEA Nanoscience , 28049 Madrid, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: Álvarez-Asencio
authors.affiliation: Department of Pharmacy, Uppsala University , P.O. Box 580, SE-752 32 Uppsala, Sweden.
authors.forename: Göran
authors.initials: G
authors.lastname: Frenning
authors.affiliation: School of Materials, The University of Manchester , MSS Tower, Manchester M13 9PL, United Kingdom.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Saunders
authors.affiliation: Department of Surface and Corrosion Science, School of Chemical Science and Engineering, KTH Royal Institute of Technology , SE-100 44 Stockholm, Sweden.|SP Technical Research Institute of Sweden, SP Chemistry, Materials and Surfaces , SE-114 86 Stockholm, Sweden.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Rutland
authors.affiliation: Department of Pharmacy, Uppsala University , P.O. Box 580, SE-752 32 Uppsala, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Malmsten
keywords: atomic force microscopy; finite element method; microgel; pH-responsive; quartz crystal microbalance; surface-bound