Hierarchical Nanostructure Control in Rod−Coil Block Copolymers with Magnetic Fields

Tao, Yudong; Zohar, Hagar; Olsen, Bradley D.; Segalman, Rachel A.

doi:10.1021/nl0712320

Cited by 88 publications

(100 citation statements)

References 25 publications

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“…Using a brush layer that presents a neutral surface to both blocks may help, although it would have to be a good conductor at the same time. Other ordering techniques, such as using magnetic fields [75] may also be adequate. …”

Section: Requirements On the Nanostructure Of Conjugated Bcps For Phomentioning

confidence: 99%

Block Copolymer Nanostructures for Technology

2010

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Nanostructures generated from block copolymer self-assembly enable a variety of potential technological applications. In this article we review recent work and the current status of two major emerging applications of block copolymer (BCP) nanostructures: lithography for microelectronics and photovoltaics. We review the progress in BCP lithography in relation to the requirements of the semiconductor technology roadmap. For photovoltaic applications, we review the current status of the quest to generate ideal nanostructures using BCPs and directions for future research.

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Section: Requirements On the Nanostructure Of Conjugated Bcps For Phomentioning

confidence: 99%

Block Copolymer Nanostructures for Technology

2010

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“…Prior work has relied on liquid crystalline (LC) [7][8][9][10] or crystalline [11] assembly of rigid moities integrated with the BCP to achieve a sufficiently large ∆χ for alignment at reasonable field strengths. Prototypical mesogenic units such as cyanobiphenyl species have ∆χ ≈ 10 −6 (in SI dimensionless volume units) [12,13].…”

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confidence: 99%

Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

et al. 2015

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We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed selfassembly of a block copolymer using in situ X-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, ∆χ, that drives alignment, and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding ∆χ ≈ 2 × 10 −8 . From field-dependent scattering data we estimate grains of ≈ 1.2 µm are present during alignment. These results demonstrate that intrinsic anisotropy is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.

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“…Attempts to isolate the contribution from the BCP structure by subtraction of the contribution to the scattering signal from only the particles proved unsuccessful. An oriented BCP array is expected to yield a mirror-image pair of spots or crescents of intensity, 16 as opposed to the isotropic ring of intensity observed for unoriented samples. In Figure 3c, the lemon-shaped scattering pattern arises from the form factor of the (partially oriented) particles, 22 dwarfing the signal from the BCP.…”

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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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Hierarchical Nanostructure Control in Rod−Coil Block Copolymers with Magnetic Fields

Cited by 88 publications

References 25 publications

Block Copolymer Nanostructures for Technology

Block Copolymer Nanostructures for Technology

Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

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

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