title: Self-Organization of Polystyrene-b-polyacrylic Acid (PS-b-PAA) Monolayer at the Air/Water Interface: A Process Driven by the Release of the Solvent Spreading.
abstract: We present an in situ structural study of the surface behavior of PS-b-PAA monolayers at the air/water interface at pH 2, for which the PAA blocks are neutral and using N,N-dimethyformamide (DMF) as spreading solvent. The surface pressure versus molecular area isotherm shows a perfectly reversible pseudoplateau over several cycles of compression/decompression. The width of such plateau enlarges when increasing temperature, conversely to what is classically observed in the case of an in-plane first order transition. We combined specular neutron reflectivity (SNR) experiments with contrast variation to solve the profile of each block perpendicular to the surface with grazing-incidence small-angle scattering (GISAXS) measurements to determine the in-plane structure of the layer. SNR experiments showed that both PS and PAA blocks remain adsorbed on the surface for all surface pressure probed. A correlation peak at Q(xy)* = 0.021 Å(-1) is evidenced by GISAXS at very low surface pressure which intensity first increases on the plateau. When compressing further, its intensity decays while Q(xy)* is shifted toward low Q(xy). The peak fully disappears at the end of the plateau. These results are interpreted by the formation of surface aggregates induced by DMF molecules at the surface. These DMF molecules remain adsorbed within the PS core of the aggregates. Upon compression, they are progressively expelled from the monolayer, which gives rise to the pseudoplateau on the isotherm. The intensity of the GISAXS correlation peak is set by the amount of DMF within the monolayer as it vanishes when all DMF molecules are expelled. This result emphizes the role of the solvent in Langmuir monolayer formed by amphiphilic copolymers which hydrophobic and hydrophilic parts are composed by long polymer chains.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS-UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu F-75005 Paris, France.|Laboratoire Léon Brillouin, CEA Saclay, 91191 Gif sur Yvette Cedex, France.
authors.forename: Zineb
authors.initials: Z
authors.lastname: Guennouni
authors.affiliation: Laboratoire Léon Brillouin, CEA Saclay, 91191 Gif sur Yvette Cedex, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Cousin
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS-UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu F-75005 Paris, France.|Faculté des Sciences Fondamentales et Biomédicales, Université Paris Descartes , 45 rue des Saints Pères , 75006 Paris, France.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Fauré
authors.affiliation: Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI), ParisTech, PSL Research University, Sciences et Ingénierie de la Matière Molle (SIMM), CNRS UMR 7615, 10, Rue Vauquelin, F-75231 Cedex 05 Paris, France.|Sorbonne-Universités, UPMC Univ Paris 06, SIMM, 10, Rue Vauquelin, F-75231 Cedex 05 Paris, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Perrin
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS-UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu F-75005 Paris, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Limagne
authors.affiliation: European Synchrotron Radiation Facility , 6 rue Jules Horowitz 38000 Grenoble, France.
authors.forename: Oleg
authors.initials: O
authors.lastname: Konovalov
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS-UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu F-75005 Paris, France.|Faculté des Sciences Fondamentales et Biomédicales, Université Paris Descartes , 45 rue des Saints Pères , 75006 Paris, France.|Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Goldmann