English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

For the past∼30 years, polymer nanocomposites (PNCs) and block copolymers (BCPs) have represented two extremely active areas of research within the polymer science community. It was inevitable, then, that the two topics should overlap; block copolymer/nanoparticle composites represent a relatively new and exciting field in materials research. A large portion of such workhas, to date, sought to employ thewell-orderedmicrophaseseparated structures available in block copolymers as scaffolds to direct the spatial arrangement of the nanofiller. Indeed, effective control over the spatial location and/or orientation of the nanofiller particles in PNCs offers great possibilities for dramatically improved composite properties. In the block copolymer field, great strides have been made in developing techniques to globally orient the BCPmicrodomains using external fields (e.g., shear or electric fields) or surfaces, even further enhancing the possibility for the creation of nanocomposites with precisely defined morphology. In this Communication,we present a generalmethod for creation of aligned block copolymer/nanoparticle (BCP/NP) composites, although via something of an inverse approach: an external (magnetic) field is used to define the spatial orientation of rodshapedmagneticNPs,which then serve as structure-directing agents for neighboringBCPdomains. Specifically, the orientedNPs,which are incorporated at a concentration of only a few percent, present templating surfaces for the alignmentof cylindrical block copolymer nanodomains. In a sense, our approach is an extrapolation of the graphoepitaxy technique, which can be used to template BCP cylinder orientation in thin films, to thicker films, and eventually into the bulk. The ability of rod-shaped NPs to nucleate coaxially oriented BCP cylinders has recently been established. There has alsobeena fair amountofworkusingmagnetic fields toorient block copolymers, although it is necessary to use copolymers which contain moieties or semicrystalline domains with appreciable magnetic susceptibility. In the absence of such a condition, we introduced the rod-shapednanoparticles,whichare capableofbeing magnetically aligned.Using this kind of scheme to induce reorientation in lyotropic liquid crystal/nanomagnet composites has also been demonstrated. The composite under study consisted of a polystyrene-blockpoly(2-vinylpyridine) (PS-P2VP) diblock copolymer, which forms cylindrical microdomains of P2VP in a PS matrix, and spindletype hematite (R-Fe2O3) particles, which were synthesized by the forced hydrolysis of Fe(ClO4)3, according to procedures previously described by Oca~ na et al. The particles, an example of which is shown in the transmission electron microscopy (TEM) image in Figure 1a, had an average diameter of 55 ( 6 nm and an average long axis length of 330 ( 38 nm (see the Supporting Information, Figure S1). Such hematite particles are weakly ferromagnetic and have recently been shown to orient with their major axes perpendicular to an applied magnetic field, B, as drawn in Figure 1b (B applied in thex-direction). Toovercome this problemand introduce a unique particle orientation, the composites were cast as films of thickness∼500 nm; by confining the particles to lie in the film plane and perpendicular to the appliedmagnetic field, the particles should orient preferentially in the y-direction diagrammed in Figure 1c. Films were produced by casting a THF solution of BCP (1 wt %) and NP (0.05 wt %) onto either carbon-coated epoxy or mica substrates, followed by slow solvent evaporation. For samples subjected to the magnetic field, the substrate was placed between two permanent magnets and the solution casting procedure followed. To allow the BCP microstructure to evolve toward equilibrium, the films were annealed in CH2Cl2 solvent vapor (a neutral solvent for PS and P2VP) for 1 day while still under the influence of the magnetic field. This process resulted in the alignment of the BCP cylinders with Figure 1. (a) TEM image of a typical needle-shaped hematite particle. (b) The particles orient in the plane perpendicular to the applied magnetic field, B. (c) Confining the particles to lie within the block copolymer film parallel to the substrate, and under the influence of B, should result in a unique particle orientation. (d) The preferred BCP cylinder orientation is parallel to both the substrate and the long axis of neighboring hematite nanoparticles.

Mutual Alignment of Block Copolymer−Magnetic Nanoparticle Composites in a Magnetic Field