Nematoelasticity of hybrid molecular-colloidal liquid crystals

Senyuk, Bohdan; Mundoor, Haridas; Smalyukh, Ivan I.; Wensink, H. H.

doi:10.1103/physreve.104.014703

Cited by 4 publications

(4 citation statements)

References 102 publications

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“…At the same time, elastic constants of the LC‐GNPB composite can also change by ≈10% comparing to a pristine 5CB due to interactions between the individual nanoparticles with the embedding solvent through surface‐anchoring forces and colloidal interactions between nanoparticles themselves. [ 27 ] Overall, our findings reveal that doping of the LC with GNPBs only modestly changes the LC‐GNPB composite's switching characteristics as compared to that of the LC host medium.…”

Section: Resultsmentioning

confidence: 78%

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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Section: Resultsmentioning

confidence: 78%

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

et al. 2021

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“…The electrostatics analogy, however, provides the initial set of considerations for designing interactions and self-assembly of nematic colloids. ,,,,− , External stimuli, such as light and electric or magnetic fields, can be used to reconfigure interactions between the nematic colloids, including the very possibility of turning attractive interactions into repulsive interactions and vice versa . The use of electrostatic interactions enabled by the colloidal particle’s surface charging , allows for counterbalancing the anisotropic (including strongly attractive) forces arising due to the orientational elasticity of LCs with the (Coulomb-like) electrostatic repulsive interactions, which helps to eliminate the issue of too strong binding (thousands of k B T ) between nematic colloidal objects that cannot be overcome by the strength of thermal fluctuations. − Thus, LC host media provide a versatile platform for controlling both the anisotropy and the strength of the interparticle forces, which is essential for controlling their self-assembly. This approach already helped to realize molecular–colloidal analogs of orthorhombic and monoclinic biaxial nematic fluids, ferromagnetic (chiral) nematic LC colloids, triclinic and other colloidal crystals, and so on.…”

Section: Discussionmentioning

confidence: 99%

“…Boundary conditions at the colloids’ surface determine n ( r )-deformations around the colloidal particles immersed into LC and formation of the corresponding elastic multipoles. ,, Therefore, controlling the boundary conditions especially when colloids already are mixed in the dispersions can affect the self-assembly of colloidal particles resulting in different fluid materials with new symmetry. − Examples of boundary conditions that can be obtained for LC molecules using specific alignment agents at different colloidal particles described in this article are summarized in Table . One of the methods of controlling the type of anchoring at the colloids’ surface is using electrostatic charging of their surface (Figure ).…”

Section: Liquid Crystal Colloids Fabrication Methodsmentioning

confidence: 99%

Design and Preparation of Nematic Colloidal Particles

2022

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Colloidal systems are abundant in technology, in biomedical settings, and in our daily life. The so-called “colloidal atoms” paradigm exploits interparticle interactions to self-assemble colloidal analogs of atomic and molecular crystals, liquid crystal glasses, and other types of condensed matter from nanometer- or micrometer-sized colloidal building blocks. Nematic colloids, which comprise colloidal particles dispersed within an anisotropic nematic fluid host medium, provide a particularly rich variety of physical behaviors at the mesoscale, not only matching but even exceeding the diversity of structural and phase behavior in conventional atomic and molecular systems. This feature article, using primarily examples of works from our own group, highlights recent developments in the design, fabrication, and self-assembly of nematic colloidal particles, including the capabilities of preprogramming their behavior by controlling the particle’s surface boundary conditions for liquid crystal molecules at the colloidal surfaces as well as by defining the shape and topology of the colloidal particles. Recent progress in defining particle-induced defects, elastic multipoles, self-assembly, and dynamics is discussed along with open issues and challenges within this research field.

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“…Although the discovery of liquid crystals (LCs) dates back more than a century ago, LCs are still studied eagerly in an effort to search for new materials that meet the constantly growing need of applications in biosensors and organic transistors [1,2] and to further our scientific understanding self-organization of soft condensed matter in the presence of external fields such as geometric confinement [3][4][5]. As a benchmark model colloidal particles with a simple non-isotropic shape, such as rods and discs, have been analyzed extensively in theory [6][7][8][9], experiment [10,11] and by computer simulation [12][13][14]. Onsager (1949) [15,16] argued that the key factor in the formation of liquid crystalline structures is the anisotropic shape of the particles for which simple geometrical shapes are usually considered, such as ellipsoids [13,17] cylindrical rods [18], cut spheres [19], or parallelepipeds [20,21].…”

Section: Introductionmentioning

confidence: 99%

Capillary-driven biaxial planar and homeotropic nematization of hard cylinders

2022

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We use the Parsons-Lee modification of Onsager's second virial theory within the restricted orientation (Zwanzig) approximation to analyse the phase behaviour of hard cylindrical rods confined in narrow pores. Depending on the wall-to-wall separation we predict a number of distinctly different surfacegenerated nematic phases, including a biaxial planar nematic with variable number of layers, a monolayer homeotropic, and a hybrid T-type structure (a planar layer combined with a homeotropic one). For narrow pores, we find evidence of two types of second-order uniaxial-biaxial transitions depending on the aspect ratio of the particles. More specifically, we observe a continuous cross-over from n to n+1 layers each with a distinct planar anchoring symmetry as well as first-order transitions from planar to homeotropic surface anchoring. Contrary to the previously studied case of parallelepipeds we find that the surface anchoring transition from planar to homeotropic symmetry occurs at much lower overall rod packing fractions. This renders the observation of homeotropic capillary nematics much more realistic in experimental systems of strongly confined anisotropic colloids. Unlike confined parallelepipeds, cylindrical rods gradually increase the number of the nematic planar layers (without any phase transitions). However, a weak first order transition was observed between two planar structures with n and n+1 layers in wide pores and longer rods. In addition, the cylindrical rods exhibit a first-order transition from the homeotropic structure to the uniaxial (or biaxial) T phase that has not been observed in confined hard parallelepipeds. We further demonstrate a reentrant uniaxial-biaxial-uniaxial-biaxal phase sequence for confined cylinders at small aspect ratio. Our results also clearly demonstrate that stable T-type surface ordering is a subtle capillary effect that only becomes manifest in sufficiently narrow pores away from the 2D bulk limit.

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Nematoelasticity of hybrid molecular-colloidal liquid crystals

Cited by 4 publications

References 102 publications

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

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

Design and Preparation of Nematic Colloidal Particles

Capillary-driven biaxial planar and homeotropic nematization of hard cylinders

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