Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

Rokhlenko, Yekaterina; Gopinadhan, Manesh; Osuji, Chinedum O.; Zhang, Kai; O’Hern, Corey S.; Larson, Steven R.; Gopalan, Padma; Majewski, Paweł; Yager, Kevin G.

doi:10.1103/physrevlett.115.258302

Cited by 54 publications

(55 citation statements)

References 40 publications

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“…These values represent the characteristic dimensions for grains which at steady state would reproduce the field-dependent orientation distributions observed experimentally. This steady-state assumption and the fact that the degree of alignment observed experimentally is dependent on the cooling rate suggests that the inferred grain sizes underestimate the actual grain sizes to some degree, as observed in prior work (16).…”

Section: Resultssupporting

confidence: 60%

“…(7)(8)(9)(10)(11)(12)(13)(14)(15) The LC mesophase within the BCP superstructure provides a ≈100-to 1,000-fold increase in ∆χ relative to non-LC BCPs. Conversely, recent work has demonstrated that the intrinsic susceptibility anisotropy (∆χ ≈ 10 −8 ) of non-LC BCPs can be sufficient to provide strong alignment at field strengths of 5-6 T, due to the large grain sizes produced in certain low-molecular-weight BCPs, with ξ > 1 µm (16,17). The aforementioned cases contrast sharply with smallmolecule LCs where alignment can be driven readily at fields below 1 T (18)(19)(20).…”

Section: Magnetic-field Dsa Of Bcpsmentioning

confidence: 98%

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Controlling orientational order in block copolymers using low-intensity magnetic fields

Gopinadhan

Choo

Kawabata

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP's anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields (<0.5 T) that are accessible using permanent magnets, in contrast to the high fields (>4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system's nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles.

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Section: Resultssupporting

confidence: 60%

Section: Magnetic-field Dsa Of Bcpsmentioning

confidence: 98%

Controlling orientational order in block copolymers using low-intensity magnetic fields

Gopinadhan

Choo

Kawabata

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Rokhlenko et al, using transmission electron microscopy (TEM), demonstrated that magnetic field produces alignment of polymer microdomains which are sensitive to temperature and magnetic field strength. 42 Their work, however, involved high magnetic fields up to 6 T, which is significantly higher than the 0.35 T B-field used in the MRIgRT system used in our work. Due to the presence of magnetic field during irradiation, the film response may change due to the formation of polymer microdomains 42 and production of longer polymer chains.…”

Section: Discussionmentioning

confidence: 81%

Influence of 0.35 T magnetic field on the response of EBT3 and EBT‐XD radiochromic films

et al. 2020

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To investigate the inconsistency of recent literature on the effect of magnetic field on the response of radiochromic films, we studied the influence of 0.35 T magnetic field on dosimetric response of EBT3 and EBT-XD Gafchromic TM films. Methods: Two different models of radiochromic films, EBT3 and EBT-XD, were investigated. Pieces of films samples from two different batches for each model were irradiated at different dose levels ranging from 1 to 20 Gy using 6 MV flattening filter free (FFF) x-rays generated by a clinical MR-guided radiotherapy system (B = 0.35 T). Film samples from the same batch were irradiated at corresponding dose levels using 6 MV FFF beam from a conventional linac (B = 0) for comparison. The net optical density was measured 48 h postirradiation using a flatbed scanner. The absorbance spectra were also measured over 500-700 nm wavelength range using a fiber-coupled spectrometer with 2.5 nm resolution. To study the effect of fractionated dose delivery to EBT3 (/EBT-XD) films, 8 (/16) Gy dose was delivered in four 2 (/4) Gy fractions with 24 h interval between fractions. Results: No significant difference was found in the net optical density and net absorbance of the films irradiated with or without the presence of magnetic field. No dependency on the orientation of the film during irradiation with respect to the magnetic field was observed. The fractionated dose delivery resulted in the same optical density as delivering the whole dose in a single fraction. Conclusions: The 0.35 T magnetic field employed in the ViewRay ® MR-guided radiotherapy system did not show any significant influence on the response of EBT3 and EBT-XD Gafchromic TM films.

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“…However, for most applications precise control over orientation with a minimum amount of defects is favorable. Different techniques have been established to obtain highly aligned samples from block copolymers, for example the application of external stimuli such as magnetic 13,14 or electric fields, 15 shear force, 16,17 temperature gradients, 18 and patterned substrates [19][20][21] have been thoroughly investigated.…”

Section: Introductionmentioning

confidence: 99%

Reorientation mechanisms of block copolymer/CdSe quantum dot composites under application of an electric field

et al. 2016

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Time- and temperature-resolved in situ birefringence measurements were applied to analyze the effect of nanoparticles on the electric field-induced alignment of a microphase separated solution of poly(styrene)-block-poly(isoprene) in toluene. Through the incorporation of isoprene-confined CdSe quantum dots the reorientation behavior is altered. Particle loading lowers the order-disorder transition temperature, and increases the defect density, favoring nucleation and growth as an alignment mechanism over rotation of grains. The temperature dependent alteration in the reorientation mechanism is analyzed via a combination of birefringence and synchrotron SAXS. The detailed understanding of the effect of nanoparticles on the reorientation mechanism is an important prerequisite for optimization of electric-field-induced alignment of block copolymer/nanoparticle composites where the block copolymer guides the nanoparticle self-assembly into anisotropic structures.

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Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

Cited by 54 publications

References 40 publications

Controlling orientational order in block copolymers using low-intensity magnetic fields

Controlling orientational order in block copolymers using low-intensity magnetic fields

Influence of 0.35 T magnetic field on the response of EBT3 and EBT‐XD radiochromic films

Reorientation mechanisms of block copolymer/CdSe quantum dot composites under application of an electric field

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