title: Structure of Multiresponsive Brush-Decorated Nanoparticles: A Combined Electrokinetic, DLS, and SANS Study.
abstract: Particles consisting of a glassy poly(methyl methacrylate) core (ca. 40 nm in radius) decorated with a poly(N-isopropylacrylamide) anionic corona are synthesized using either methacrylic acid (MA) or acrylic acid (AA) as reactive comonomers in the shell. The different reactivity ratios of MA and AA toward N-isopropylacrylamide originates p(MA-N) and p(N-AA) particles with carboxylate charges supposedly located, preferentially, in the close vicinity of the core and at the shell periphery, respectively. The corresponding swelling features of these nanoparticles are addressed over a broad range of pH values (4 to 7.5), NaNO3 concentrations (3 to 200 mM), and temperatures (15 to 45 °C) by dynamic light scattering (DLS) and small angle neutron scattering (SANS). DLS shows that the swelling of the particle shells increases their thickness from ∼10 to 90 nm with decreasing temperature, ionic strength, or increasing pH, with the effect being more pronounced for p(N-AA) whose lower critical solution temperature is shifted to higher values compared to that of p(MA-N). Potentiometric titration and electrokinetic results further reflect the easier dissociation of carboxyl groups in p(N-AA) and a marked heterogeneous interfacial swelling of the latter with decreasing solution salt content. The DLS response of both particles is attributed to the multiresponsive nature of a peripheral dilute shell, while SANS only probes the presence of a quasi-solvent-free dense polymer layer, condensed on the core surface. The thickness of that layer slightly increases from ∼6 to 9.5 nm with increasing temperature from 15 to 45 °C (at 15 mM NaNO3 and pH 5) due to the collapse of the outer dilute shell layer. Overall, results evidence a nonideal brush behavior of p(MA-N) and p(N-AA) and their microphase segregated shell structure, which supports some of the conclusions recently formulated from approximate self-consistent mean-field computations.
authors.affiliation: †CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR7360, Vandoeuvre-lès-Nancy F-54501, France.|‡Université de Lorraine, LIEC, UMR7360, Vandoeuvre-lès-Nancy F-54501, France.
authors.forename: Jennifer R S
authors.initials: JR
authors.lastname: Martin
authors.affiliation: †CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR7360, Vandoeuvre-lès-Nancy F-54501, France.|‡Université de Lorraine, LIEC, UMR7360, Vandoeuvre-lès-Nancy F-54501, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bihannic
authors.affiliation: §Centro de Quimica Fisica Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tecnico, University of Lisbon, 1049-001 Lisboa, Portugal.
authors.forename: Catarina
authors.initials: C
authors.lastname: Santos
authors.affiliation: §Centro de Quimica Fisica Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tecnico, University of Lisbon, 1049-001 Lisboa, Portugal.
authors.forename: José Paulo S
authors.initials: JP
authors.lastname: Farinha
authors.affiliation: ∥Institut Laue-Langevin (ILL), BP 156-X, F-38042 Grenoble Cedex, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Demé
authors.affiliation: ⊥Laboratory of Physical Chemistry and Colloid Science, Wageningen University and Research Center, Dreijenplein 8, 6703 HB Wageningen, The Netherlands.
authors.forename: Frans A M
authors.initials: FA
authors.lastname: Leermakers
authors.affiliation: †CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR7360, Vandoeuvre-lès-Nancy F-54501, France.|‡Université de Lorraine, LIEC, UMR7360, Vandoeuvre-lès-Nancy F-54501, France.
authors.forename: José P
authors.initials: JP
authors.lastname: Pinheiro
authors.affiliation: †CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR7360, Vandoeuvre-lès-Nancy F-54501, France.|‡Université de Lorraine, LIEC, UMR7360, Vandoeuvre-lès-Nancy F-54501, France.
authors.forename: Elise
authors.initials: E
authors.lastname: Rotureau
authors.affiliation: †CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR7360, Vandoeuvre-lès-Nancy F-54501, France.|‡Université de Lorraine, LIEC, UMR7360, Vandoeuvre-lès-Nancy F-54501, France.
authors.forename: Jérôme F L
authors.initials: JF
authors.lastname: Duval