Optical patterning of magnetic domains and defects in ferromagnetic liquid crystal colloids

Hess, Andrew J.; Liu, Qingkun; Smalyukh, Ivan I.

doi:10.1063/1.4928552

Cited by 33 publications

(31 citation statements)

References 22 publications

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“…For a BFLCC with the downcone orientation of M with respect to n 0 this behavior is completely reversed but consistent from the standpoint of the mutual orientations of B, M, and n 0 , showing that switching is polar (Fig. 2B) but different from that of uniaxial ferromagnetic LC colloids (9)(10)(11)(12). BFLCCs exhibit hysteresis for M-components parallel and perpendicular to n 0 ( Fig.…”

Section: Significancementioning

confidence: 86%

“…2E) cells with n 0 perpendicular and parallel to confining substrates, respectively, as well as for orientations of applied field B and measured M-components parallel and perpendicular to n 0 . Resisted by elastic energy costs of director distortions, magnetic switching of single-domain BFLCCs is threshold-free for fields applied in directions parallel and perpendicular to n 0 and is different from that of uniaxial ferromagnetic LC colloids (6)(7)(8)(9)(10)(11)(12). The field Bkn 0 applied to a BFLCC with n 0 along the cell normal z, with a tilted M spontaneously along one of the orientations on the up-cone, rotates M toward B and thereby tilts the director away from the confining surface normal, leading to light transmission through the sample placed between crossed polarizers (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…As in uniaxial ferromagnetic LC dispersions (7,8,(9)(10)(11)(12), preparation of BFLCCs can involve quenching of the LC host from the isotropic phase in an external B, which can produce upcone or down-cone orientation of M within the entire sample. Alternatively, polydomain BFLCCs are obtained from a paramagnetic colloidal dispersion with initially random up-and down-cone orientations of m of FNPs by applying B to separate them into a sample of multidomains of opposite cone orientation (Fig.…”

Section: (E-h)mentioning

confidence: 99%

“…At the same time, there is a great potential for guiding low-symmetry assembly in hybrid LC-colloidal systems, in which the molecular LC is a fluid host for colloidal particles (18). Different types of LCmediated ordering of anisotropic particles can emerge from elastic and surface-anchoring-based interactions and can lead to the spontaneous polar alignment of magnetic inclusions (6), although the orientations of the magnetic dipoles of colloidal particles were always slave to the LC director n, orienting either parallel or perpendicular to it without breaking uniaxial symmetry (6)(7)(8)(9)(10)(11)(12).…”

mentioning

confidence: 99%

“…Fluids with polar ordering were envisaged by Born a century ago (3)(4)(5), with their study recently guided by prescient theories of Brochard and de Gennes (6)(7)(8)(9)(10)(11)(12). An experimental search for small-molecule biaxial nematic fluids has gone on for decades (2,13).…”

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confidence: 99%

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Biaxial ferromagnetic liquid crystal colloids

Liu

Ackerman

Lubensky

et al. 2016

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

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The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed "director," whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light.iquid crystals (LCs) that combine fluidity with many forms of orientational and partial positional order are ubiquitous (1, 2). Fluids with polar ordering were envisaged by Born a century ago (3-5), with their study recently guided by prescient theories of Brochard and de Gennes (6-12). An experimental search for small-molecule biaxial nematic fluids has gone on for decades (2, 13). Many types of low-symmetry ordering have been found in smectic and columnar systems (14, 15) with fluidity in only two and one dimensions, respectively (1). However, nematic LCs with 3D fluidity and no positional order tend to be nonpolar, although phases with polar and biaxial structure have been considered (15)(16)(17). In colloids, such as aqueous suspensions of rods and platelets, nonpolar uniaxial ordering is also predominant (1, 18). At the same time, there is a great potential for guiding low-symmetry assembly in hybrid LC-colloidal systems, in which the molecular LC is a fluid host for colloidal particles (18). Different types of LCmediated ordering of anisotropic particles can emerge from elastic and surface-anchoring-based interactions and can lead to the spontaneous polar alignment of magnetic inclusions (6), although the orientations of the magnetic dipoles of colloidal particles were always slave to the LC director n, orienting either parallel or perpendicular to it without breaking uniaxial symmetry (6-12).In this work, by controlling surface anchoring of colloidal magnetic nanoplates in a nematic host, we decouple the polar ordering of magnetic dipole moments described by macroscopic magnetization M from the nonpolar director n describing the orientational ordering of the LC host molecules. The ensuing biaxial ferromagnetic LC colloids (BFLCCs) possess 3D fluidity and simultaneous polar ferromagnetic and biaxial order. Direct imaging of nanoplates and their magnetic moment orientations relative to n and holonomic control of fields that strongly couple to M and reveal their orientations, as well as numer...

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Section: Significancementioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Section: (E-h)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Biaxial ferromagnetic liquid crystal colloids

Liu

Ackerman

Lubensky

et al. 2016

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

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Read on Demand Images in Laser‐Written Polymerizable Liquid Crystal Devices

Tartan

O’Neill

Salter

et al. 2018

Advanced Optical Materials

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Two‐photon laser writing is a powerful technique for creating intricate, high resolution features in polymerizable materials. Here, using a single‐step process to microfabricate polymer inclusions, the ability to generate read‐on‐demand images and identification codes in a liquid crystal (LC) device is demonstrated. These micrometer‐sized polymer features are encoded directly into LC devices using direct laser writing, which locks‐in the local molecular orientation at the moment of fabrication. By reading the devices with the same voltage amplitude that is used to write the polymer structures, features can be made to disappear as the director profile becomes homogeneous with the surrounding regions, effectively cloaking the structure for both polarized and unpolarized light. It is shown how this process can be used to create micrometer‐scale reconfigurable emoticons and quick‐response codes within a fully assembled LC device, with potential use in authenticity and identification applications.

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Nematic Order, Plasmonic Switching and Self‐Patterning of Colloidal Gold Bipyramids

et al. 2021

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Dispersing inorganic colloidal nanoparticles within nematic liquid crystals provides a versatile platform both for forming new soft matter phases and for predefining physical behavior through mesoscale molecular-colloidal self-organization. However, owing to formation of particle-induced singular defects and complex elasticity-mediated interactions, this approach has been implemented mainly just for colloidal nanorods and nanoplatelets, limiting its potential technological utility. Here, orientationally ordered nematic colloidal dispersions are reported of pentagonal gold bipyramids that exhibit narrow but controlled polarization-dependent surface plasmon resonance spectra and facile electric switching. Bipyramids tend to orient with their C 5 rotation symmetry axes along the nematic director, exhibiting spatially homogeneous density within aligned samples. Topological solitons, like heliknotons, allow for spatial reorganization of these nanoparticles according to elastic free energy density within their micrometer-scale structures. With the nanoparticle orientations slaved to the nematic director and being switched by low voltages ≈1 V within a fraction of a second, these plasmonic composite materials are of interest for technological uses like color filters and plasmonic polarizers, as well as may lead to the development of unusual nematic phases, like pentatic liquid crystals.

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Optical patterning of magnetic domains and defects in ferromagnetic liquid crystal colloids

Cited by 33 publications

References 22 publications

Biaxial ferromagnetic liquid crystal colloids

Biaxial ferromagnetic liquid crystal colloids

Read on Demand Images in Laser‐Written Polymerizable Liquid Crystal Devices

Nematic Order, Plasmonic Switching and Self‐Patterning of Colloidal Gold Bipyramids

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