The isotropic-nematic interface of colloidal goethite in an external magnetic field

Pol, E. van den; Lupascu, A.; Vroege, G. J.

doi:10.1063/1.3498738

Cited by 12 publications

(11 citation statements)

References 20 publications

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“…In applications to manufacturing of high density recording films and discs, spin alignment is required to carry the recorded information when spins in magnetic nanorods are prone to align parallel to the nanorod axis . In optical applications, magnetic liquid crystals are attractive candidates for making reconfigurable magnetooptical devices with the fast time response measured in milliseconds …”

Section: Introductionmentioning

confidence: 99%

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

Kornev

2016

Adv Funct Materials

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3796 wileyonlinelibrary.com nanorods as the fi llers are believed to be the best candidates for materials working in extreme environment and hence they are on demand in aerospace and space exploration applications. [39][40][41][42][43] In composite fi lms needed for inductor and antennae applications, the alignment of magnetic particles is required to increase the high frequency permeability and to lower the hysteresis losses. [44][45][46][47] In applications to manufacturing of high density recording fi lms and discs, spin alignment is required to carry the recorded information when spins in magnetic nanorods are prone to align parallel to the nanorod axis. [ 37,[48][49][50] In optical applications, magnetic liquid crystals are attractive candidates for making reconfi gurable magnetooptical devices with the fast time response measured in milliseconds. [11][12][13][14][15][16][17][18][51][52][53] In all these applications, one needs to control the alignment of magnetic nanorods in liquid medium. Therefore, this problem is actively discussed in the literature; however, the general strategy for making macroscopic samples with ordered nanorods has not been developed yet and it remains the main challenge of materials engineering [32][33][34][35][39][40][41][42]54 ] Processing of multifunctional coatings and thin fi lms require many steps and hence one needs to control the fi lm properties at each step.Rheological properties of the fi lms at each stage of their processing play the most important role in nanorod ordering and keeping nanorods in place. Characterization of thin coating fi lms during composite manufacturing remains challenging. Different experimental methods have been proposed and developed for in situ characterization of rheological properties of thin fi lms and coatings. [ 20,[25][26][27][55][56][57][58][59][60] It appears that unique features of rotation of ferromagnetic nanorods can be used for characterization of very thin fi lms when other methods fall short. Recently introduced magnetic rotational spectroscopy (MRS) with nanoparticles and nanorods allows one to probe fl uid rheology in very thin fi lms and nanoliter droplets. [ 12,20,22,25,60,61 ] MRS takes advantage of a distinguishable behavior of rotating magnetic tracers as the frequency of applied rotating fi eld changes. Unlike many methods based on the analysis of small oscillations, which are diffi cult to interpret when the fi lm is very thin, MRS with magnetic nanorods enjoys analysis of full revolutions of magnetic tracers. [ 20,22,24,25,60,62,63 ] Understanding of the characteristic features of rotation of a single nanorod in complex fl uids and alignment of an assembly

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Section: Introductionmentioning

confidence: 99%

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

Kornev

2016

Adv Funct Materials

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“…The recently discovered magnetic-field-induced (parallel) nematic-(perpendicular) nematic phase separation in goethite [22,31] can be studied using polarization microscopy, despite the intense colour of goethite dispersions. Interference colours due to sufficiently small optical path length differences can be distinguished and be interpreted using a modified birefringence colour spectrum, although care should be taken since actual colours depend on goethite concentrations, camera sensitivity and exposure times.…”

Section: Resultsmentioning

confidence: 99%

Magnetic-field-induced nematic–nematic phase separation and droplet formation in colloidal goethite

Pol¹,

Verhoeff²,

Lupascu³

et al. 2011

J. Phys.: Condens. Matter

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We demonstrate the suitability of polarization microscopy to study the recently discovered (parallel) nematic-(perpendicular) nematic phase separation. This novel type of phase transition is induced by applying an external magnetic field to a nematic liquid crystal of boardlike colloidal goethite and is due to an interplay between the intrinsic magnetic properties of goethite and the collective effect of liquid crystal formation. It is shown that the intense ochre colour of goethite does not preclude the use of polarization microscopy and interference colours, and that dichroism can give valuable qualitative information on the nature of the phases, their anchoring and their sedimentation and order parameter profiles. We also apply these techniques to study 'nematic-nematic tactoids': nematic droplets sedimenting within a nematic medium with mutually perpendicular orientations.

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“…This route could have been accessible to rod-like mineral colloids (Davidson and Gabriel, 2005; see Hamley, 2003). Indeed, mineral LCs (Lemaire et al, 2002; Gabriel and Davidson, 2003; Vroege et al, 2006; van den Pol et al, 2010) appear promising as “readily available” candidates with potential to provide a cooperative medium with sensitivity to environmental stimuli (Cairns-Smith, 2008), and this calls for a database of such minerals in pre-biotic locales. The route to LC phases has also been attempted directly from a mixture of organics using entropic forces for achieving self-assembly.…”

Section: Towards Cooperative Transitionsmentioning

confidence: 99%

Field-Control, Phase-Transitions, and Life’s Emergence

Mitra-Delmotte¹,

Mitra²

2012

Front. Physio.

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Instances of critical-like characteristics in living systems at each organizational level (bio-molecules to ecosystems) as well as the spontaneous emergence of computation (Langton), do suggest the relevance of self-organized criticality (SOC). But extrapolating complex bio-systems to life’s origins, brings up a paradox: how could simple organics – lacking the “soft-matter” response properties of today’s complex bio-molecules – have dissipated energy from primordial reactions (eventually reducing CO2) in a controlled manner for their “ordering”? Nevertheless, a causal link of life’s macroscopic irreversible dynamics to the microscopic reversible laws of statistical mechanics is indicated via the “functional-takeover” of a soft magnetic scaffold by organics (c.f. Cairns-Smith’s “crystal-scaffold”). A field-controlled structure offers a mechanism for boot-strapping – bottom-up assembly with top-down control: its super-paramagnetic colloidal components obey reversible dynamics, but its dissipation of magnetic (H)-field energy for aggregation breaks time-reversal symmetry. The responsive adjustments of the controlled (host) mineral system to environmental changes would bring about mutual coupling between random organic sets supported by it; here the generation of long-range correlations within organic (guest) networks could include SOC-like mechanisms. And, such cooperative adjustments enable the selection of the functional configuration by altering the inorganic dipolar network’s capacity to assist a spontaneous process. A non-equilibrium dynamics could now drive the kinetically oriented system (trimming the phase-space via sterically coupled organics) toward a series of phase-transitions with appropriate organic replacements “taking-over” its functions. Where available, experiments are cited in support of these speculations and for designing appropriate tests.

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The isotropic-nematic interface of colloidal goethite in an external magnetic field

Cited by 12 publications

References 20 publications

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

Magnetic-field-induced nematic–nematic phase separation and droplet formation in colloidal goethite

Field-Control, Phase-Transitions, and Life’s Emergence

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