title: Simultaneous Phase Transfer and Surface Modification of TiO₂ Nanoparticles Using Alkylphosphonic Acids: Optimization and Structure of the Organosols.
abstract: An original protocol of simultaneous surface modification and transfer from aqueous to organic phases of anatase TiO2 nanoparticles (NPs) using alkylphosphonic acids (PAs) is studied. The influence of the solvent, the nature and concentration of the PA, and the size, concentration, and aggregation state of the TiO2 NPs was investigated. Complete transfer was observed for linear alkyl chains (5, 8, 12, and 18 C atoms), even at very high sol concentrations. After transfer, the grafted NPs were characterized by (31)P solid-state MAS NMR. The dispersion state of NPs before and after phase transfer was monitored by dynamic light scattering (DLS). Small-angle neutron scattering (SANS) was used to characterize the structure of PA-grafted NPs in the organic solvent. Using a quantitative core-shell model cross-checked under different contrast conditions, it is found that the primary particles making up the NPs are homogeneously grafted with a solvated PA-layer. The nanometric thickness of the latter is shown to increase with the length of the linear carbon chain of the PA, independent of the size of the primary TiO2 NP. Interestingly, a reversible temperature-dependent aggregation was evidenced visually for C18PA, and confirmed by DLS and SANS: heating the sample induces the breakup of aggregates, which reassemble upon cooling. Finally, in the case of NPs agglomerated by playing with the pH or the salt concentration of the sols, the phase transfer with PA is capable of redispersing the agglomerates. This new and highly versatile method of NP surface modification with PAs and simultaneous transfer is thus well suited for obtaining well-dispersed grafted NPs.
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR 5253, CNRS-UM-ENSCM, Université de Montpellier , Place Eugène Bataillon, CC1701, F-34095 Montpellier, France.|Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier , F-34095 Montpellier, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Schmitt Pauly
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier , F-34095 Montpellier, France.
authors.forename: Anne-Caroline
authors.initials: AC
authors.lastname: Genix
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR 5253, CNRS-UM-ENSCM, Université de Montpellier , Place Eugène Bataillon, CC1701, F-34095 Montpellier, France.
authors.forename: Johan G
authors.initials: JG
authors.lastname: Alauzun
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR 5253, CNRS-UM-ENSCM, Université de Montpellier , Place Eugène Bataillon, CC1701, F-34095 Montpellier, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Guerrero
authors.affiliation: Jülich Centre for Neutron Science (JCNS), Forschungszentrum Jülich GmbH , Outstation at MLZ, Lichtenbergstraße 1, 85747 Garching, Germany.
authors.forename: Marie-Sousai
authors.initials: MS
authors.lastname: Appavou
authors.affiliation: SOLEIL Synchrotron , L'Orme des Merisiers, Gif-Sur-Yvette, 91192 Saint-Aubin, France.
authors.forename: Javier
authors.initials: J
authors.lastname: Pérez
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier , F-34095 Montpellier, France.
authors.forename: Julian
authors.initials: J
authors.lastname: Oberdisse
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR 5253, CNRS-UM-ENSCM, Université de Montpellier , Place Eugène Bataillon, CC1701, F-34095 Montpellier, France.
authors.forename: P Hubert
authors.initials: PH
authors.lastname: Mutin