Morphology and Orientational Behavior of Silica-Coated Spindle-Type Hematite Particles in a Magnetic Field Probed by Small-Angle X-ray Scattering

Reufer, Mathias; Dietsch, Hervé; Gasser, Urs; Hirt, Ann M.; Menzel, Andreas; Schurtenberger, Peter

doi:10.1021/jp911817e

Cited by 41 publications

(89 citation statements)

References 24 publications

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“…These results are comparable to results previously published by Reufer et al on silica-coated hematite particles. 38 The parameters used for fitting are summarized in Table 1. They are very close to the characteristics obtained from the TEM picture analysis, indicating that no aggregation occurred in the suspensions.…”

Section: Resultsmentioning

confidence: 99%

Single Step Hybrid Coating Process to Enhance the Electrosteric Stabilization of Inorganic Particles

et al. 2011

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Section: Resultsmentioning

confidence: 99%

Single Step Hybrid Coating Process to Enhance the Electrosteric Stabilization of Inorganic Particles

et al. 2011

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“…This is presumably the case with the hematite particles, as well, leading to the formation of a PS-P2VP brush layer that compatibilizes the particles within the PS matrix of the BCP. 27 Since the remanent magnetic moment of the particles is rather low, 22 the steric repulsion between particles afforded by this brush layer is sufficient to prevent particle aggregation in solution and in the composites. Images from cross sections cut parallel to B typically show both particles and P2VP-rich cylinder cores in cross section, as in Figure 2a,b.…”

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

et al. 2010

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For the past ∼30 years, polymer nanocomposites (PNCs) 1 and block copolymers (BCPs) 2 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 work has, to date, sought to employ the well-ordered microphaseseparated structures available in block copolymers as scaffolds to direct the spatial arrangement of the nanofiller. 3,4 Indeed, effective control over the spatial location and/or orientation of the nanofiller particles in PNCs offers great possibilities for dramatically improved composite properties. 1 In the block copolymer field, great strides have been made in developing techniques to globally orient the BCP microdomains using external fields 5 (e.g., shear 6 or electric fields 7 ) or surfaces, [8][9][10][11] even further enhancing the possibility for the creation of nanocomposites with precisely defined morphology.In this Communication, we present a general method 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 rodshaped magnetic NPs, which then serve as structure-directing agents for neighboring BCP domains. Specifically, the oriented NPs, which are incorporated at a concentration of only a few percent, present templating surfaces for the alignment of 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, 10,11 to thicker films, and eventually into the bulk. The ability of rod-shaped NPs to nucleate coaxially oriented BCP cylinders has recently been established. 12,13 There has also been a fair amount of work using magnetic fields to orient block copolymers, although it is necessary to use copolymers which contain moieties or semicrystalline domains with appreciable magnetic susceptibility. 5,[14][15][16][17] In the absence of such a condition, we introduced the rod-shaped nanoparticles, which are capable of being magnetically aligned. Using this kind of scheme to induce reorientation in lyotropic liquid crystal/nanomagnet composites has also been demonstrated. 18,19 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, 20 and spindletype hematite (R-Fe 2 O 3 ) particles, which were synthesized by the forced hydrolysis of Fe(ClO 4 ) 3 , according to procedures previously described by Ocaña et al. 21 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 hav...

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“…In particular, the magnetic moment m of the hematite core orients perpendicular to the long axis and its magnitude can be estimated taking into account the size of the core. 19 For our particles, we obtain a value of m z 9.2 Â 10 À19 J T À1 . Upon application of an external magnetic field, the long axes of the paramagnetic cores tend to align in a plane perpendicular to the field with a distribution of polar angles peaked at p/2 (Fig.…”

Section: Experiments and Resultsmentioning

confidence: 92%

“…The field strength, mB/k B T z 200, is sufficient to fully align the magnetic moments of the hematite cores along the field direction. 19 Therefore, the maximum phase shift is a measure of the saturated order parameter S 2 ¼ À1/2, corresponding to the long axis of the hematite cores aligned in a plane perpendicular to the applied magnetic field (Fig. 2a).…”

Section: Experiments and Resultsmentioning

confidence: 99%

Magnetic orientation of soft particles in a jammed solid

et al. 2012

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Densely packed atoms, molecules, or small particles can get trapped in a jammed state thereby avoiding crystallization. The resulting amorphous structures display complex, spatially heterogeneous, trapping potentials in stark contrast to the uniform case of a crystal. Here we study active and passive rotational motion in a jammed colloidal dispersion of particles consisting of an anti-ferromagnetic core and a thermo-sensitive microgel soft shell. We determine the order parameter as a function of volume fraction from optical birefringence measurements. A simple model allows us to discriminate the orientation and relaxation of different subsets of particles according to their elastic trapping state.

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Morphology and Orientational Behavior of Silica-Coated Spindle-Type Hematite Particles in a Magnetic Field Probed by Small-Angle X-ray Scattering

Cited by 41 publications

References 24 publications

Single Step Hybrid Coating Process to Enhance the Electrosteric Stabilization of Inorganic Particles

Single Step Hybrid Coating Process to Enhance the Electrosteric Stabilization of Inorganic Particles

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

Magnetic orientation of soft particles in a jammed solid

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