Synthesis of high molar masses of poly(n-butyl methacrylate)-b-polystyrene diblock copolymers by ATRP. Formation of lamellar phases in thin films

International audienceDiblock copolymers are known to self-organize in ordered domains. The morphology of this microphase separation depends essentially on the relative amount of each immiscible block in the copolymer (e.g. spherical, cylindrical, gyroidal and lamellar phases). The lamellar nanoscopic structures can serve as templates for the selective incorporation of inorganic nanoparticles , , for instance to get nanopatterned surfaces or for new applications such as wave guides. , In most of the studies concerning diblock copolymer self-assembly in lamellar periodic structures, diblock copolymers were synthesized by anionic polymerization which is a suitable technique to prepare well-defined high molar mass diblock copolymers. , In the present study, our aim is the synthesis of high molar mass poly(n-butyl methacrylate)-b-polystyrene diblock copolymers by Atom Transfer Radical Polymerization (ATRP). Compared to anionic polymerization, controlled radical polymerization (CRP) is a more versatile technique which requires less drastic experimental conditions. Our results highlight the self-assembly of the symmetric poly(n-butyl methacrylate)-b-poly(styrene) diblock copolymer synthesized by ATRP into a lamellar ordered structure after an annealing treatment

Synthèse et caractérisation de films composites dopés par des nanoparticules magnétiques

L objectif de ce travail est d élaborer des films minces composites contrôlables par un champ magnétique en incorporant des nanoparticules dans une matrice composée de copolymère dibloc symétrique s organisant en lamelles sur un substrat plan. Le copolymère dibloc symétrique P(n-BMA)-b-PS a été synthétisé par ATRP et caractérisé par diverses méthodes. L objectif étant d obtenir une masse molaire élevée, supérieure à 100 000 g/mol. Les nanoparticules sont fonctionnalisées par du polystyrène par la méthode du grafting from afin de les rendre compatibles pour qu elles puissent s insérer au sein des phases lamellaires. Puis, les films composites sont élaborés par spin coating en incorporant ces nanoparticules -Fe2O3@PS au sein du film de copolymère. Ces films sont formulés par diverses méthodes de caractérisation, notamment par réflectivité des neutrons, afin de rendre compte de l ordre lamellaire. De nouvelles particules magnétiques à base de maghémite et cobalt, CoxFe(1-x)O.Fe2O3 où le taux de cobalt x est faible (x = 3 et 7 %), sont également présentées et caractérisées.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Incorporation of magnetic nanoparticles into lamellar polystyrene-b-poly(n-butyl methacrylate) diblock copolymer films: influence of the chain end-groups on nanostructuration

In this article, we present new samples of lamellar magnetic nanocomposites based on the self-assembly of a polystyrene-b-poly(n-butyl methacrylate) diblock copolymer synthesized by atom transfer radical polymerization. The polymer films were loaded with magnetic iron oxide nanoparticles covered with polystyrene chains grown by surface initiated-ATRP. The nanostructuration of the pure and magnetically loaded copolymer films on silicon was studied by atomic force microscopy, ellipsometry, neutron reflectivity and contact angle measurement. The present study highlights the strong influence of the copolymer extremity - driven itself by the choice of the ATRP chemical route - on the order of the repetition sequences of the blocks in the multi-lamellar films. In addition, a narrower distribution of the nanoparticles' sizes was examined as a control parameter of the SI-ATRP reaction

Synthesis of block copolymers by ATRP for the combination with magnetic nanoparticles to obtain nano-composite films

Nanocomposite materials which associate inorganic nanoparticles and polymers with a high degree of organization are highly interesting for their applications in visible light optics (reflectors and guides) and hyper-frequencies (antennae and switches). We focus our study on a complex system combining self-organization of a diblock copolymer A-B and orientation properties under magnetic field of inorganic magnetic nanoparticles. We present here an experimental protocol for the synthesis by Atom Transfer Radical Polymerization (ATRP) of the symmetrical poly(n-butylmethacrylate)-b–poly(styrene) diblock copolymer (PBMA-b-PS) with high molar masses (about 100 000 g/mol). After spin-coating on a flat substrate (float glass, silicone or alumina) from a solution in a volatile solvent and annealing above the glass temperature, a thin film of such well-defined symmetrical diblocks are expected to self-organize into a lamellar (smectic type) order. The second component of the system consists in nanoparticles made of either superparamagnetic maghemite oxide Γ-Fe2O3 (soft magnets) or ferrimagnetic cobalt ferrite CoO.Fe2O3 (strong magnets). We are working on the proper dispersion of these nanoparticles within the PS blocks in order to obtain “sandwiches” made of magnetic thin layers alternating with the lamellae of the copolymer matrix. Optical Reflection Interference Contrast Microscopy (RICM) is convenient and fast to measure the thickness of the films (from a number of fringes) directly on their substrate and to detect characteristic defects of the long-range organization of the films (like holes). High resolution microscopies such as AFM and TEM will enable to measure the lamellar period but require to prepare thin films cross-sections

Neutron Reflectivity on Polymer Multilayers Doped with Magnetic Nanoparticles

International audienceThe aim of this work is to elaborate nanocomposite thin films sensitive to a magnetic field by incorporating magnetic nanoparticles in a symmetrical diblock copolymer matrix organized in lamellae on plane substrates. On the one hand, the symmetrical diblock copolymer P(n-BMA)-b-PS is synthesized by ATRP and characterized by several methods. On the other hand, nanoparticles made of maghemite Gamma-Fe2O3 are functionalized with PS using the “grafting from” technique in order to make them compatible with polystyrene and to insert them in PS lamellae. Composite films are elaborated by “spin coating” a solution containing both the Gamma-Fe2O3@PS core-shell nanoparticles and the copolymer onto a silicon substrate. After annealing, these films are characterized mainly by AFM and neutron reflectivity to investigate the lamellar order

Probing the internal structure of magnetic nanocomposites – thermo-sensitive gels and lamellar films – respectively by small angle neutron scattering and neutron reflectivity

In this poster we show two types of nanocomposite materials consisting of nanoparticles embedded in polymer matrices. On the one hand, a matrix with a high degree of organization is investigated for visible light optics and hyper-frequencies applications (reflectors, guides, antennae). On the other hand, a gel matrix with an isotropic loading of nanoparticles can exhibit a swelling transition triggered by an external field (electric or magnetic) or by temperature. The first system combines the self-assembly of a symmetrical diblock copolymer matrix poly(n-butylmethacrylate)-b–poly(styrene) (PBMA-b-PS) and the orientation properties under magnetic field of Γ-Fe2O3 nanoparticles. To confine the nanoparticles within the layers of PBMA-b-PS (Fig.1a), those were coated by a polymeric shell grown by surface initiation polymerization of PS ("grafting from"). Thin films obtained by spin-coating and annealing above the glass temperature Tg were doped with nanoparticles. The lamellar order was investigated by neutron reflectivity experiments (Fig.1b) which enable to fit the density profile of the films and to localize precisely the nanoparticles within the first PS blocs. The second system consists of the same iron oxide nanoparticles, which are confined this time within spherical clusters of PTEA-PAM (Fig.2a., cf. Pr. Perzynski), dispersed into a thermosensitive hydrogel of poly(N-isopropylacrylamide) PNIPAM. The deswelling of the matrix above the transition temperature causes the decrease of the average distance between those clusters, as shown by small angle neutron scattering experiment (Fig.2b)