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Mazzilli V, Satoh K, Saielli G. Phase behaviour of mixtures of charged soft disks and spheres. SOFT MATTER 2023; 19:3311-3324. [PMID: 37093590 DOI: 10.1039/d3sm00223c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We have investigated the phase behaviour of mixtures of soft disks (Gay-Berne oblate ellipsoids, GB) and soft spheres (Lennard-Jones, LJ) with opposite charge as a model of ionic liquid crystals and colloidal suspensions. We have used constant volume Molecular Dynamics simulations and fixed the stoichiometry of the mixture in order to have electroneutrality; three systems have been selected GB : LJ = 1 : 2, GB : LJ = 1 : 1 and GB : LJ = 2 : 1. For each system we have selected three values of the scaled point charge q* of the GB particles, namely 0.5, 1.0 and 2.0 (and a corresponding negative scaled charge of the LJ particles that depends on the stoichiometric ratio). We have found a very rich mesomorphism with the formation, as a function of the scaled temperature, of the isotropic phase, the discotic nematic phase, the hexagonal columnar phase and crystal phases. While the structure of the high temperature phases was similar in all systems, the hexagonal columnar phases exhibited a highly variable morphology depending on the scaled charge and stoichiometry. On the one hand, GB : LJ = 1 : 2 systems form lamellar structures, akin to smectic phases, with an alternation of layers of disks (exhibiting an hexagonal columnar phase) and layers of LJ particles (in the isotropic phase). On the other hand, for the 2 : 1 stoichiometry we observe the formation of a frustrated hexagonal columnar phase with an alternating tilt direction of the molecular axis. We rationalize these findings based on the structure of the neutral ion pair dominating the behaviour at low temperature and high charge.
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Affiliation(s)
- Valerio Mazzilli
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
- CNR-ITM, Institute on Membrane Technology, Padova Unit, Via Marzolo, 1, 35131 Padova, Italy
| | - Katsuhiko Satoh
- Department of Chemistry, Osaka Sangyo University, Daito, Osaka, 574-8530, Japan.
| | - Giacomo Saielli
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
- CNR-ITM, Institute on Membrane Technology, Padova Unit, Via Marzolo, 1, 35131 Padova, Italy
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Sewring T, Trulsson M. Ground State Configurations and Metastable Phases of Charged Linear Rods. ACS OMEGA 2023; 8:6040-6051. [PMID: 36816665 PMCID: PMC9933468 DOI: 10.1021/acsomega.2c08060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 01/24/2023] [Indexed: 06/18/2023]
Abstract
This computational study investigates the energy minimum, that is, ground state, of suspensions of monodisperse (single-component) charged linear rods at various densities and screening lengths. We find that closed-packed unidirectional configurations have the lowest energies for all studied cases. We further specify the lattice parameters for these crystalline structures. In addition, we identify a few metastable phases, including heliconical structures. These metastable heliconical phases are composed of hexagonal smectic C layers with particle orientations forming a conical helicoid with a short pitch of three layers. We evidence this by zero-temperature Monte Carlo simulations starting from an energy-minimized hexagonal cholesteric configuration, which rapidly transforms to a heliconical phase. Furthermore, this heliconical phase is remarkably stable even at finite temperatures and melts to a disordered phase at high temperatures. Finally, we conduct simulations at room temperature and conditions typical for cellulose nanocrystal suspensions to study the onset of nematic order and compare our results to available experimental data. Our findings suggest that electrostatics play an important role in the isotropic/anisotropic transition for dense suspensions of charged rods.
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Affiliation(s)
- Tor Sewring
- Theoretical
Chemistry, Lund University, 221 00Lund, Sweden
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Labalette V, Praga A, Girard F, Meireles M, Hallez Y, Morris JF. Shear-induced glass-to-crystal transition in anisotropic clay-like suspensions. SOFT MATTER 2021; 17:3174-3190. [PMID: 33621310 DOI: 10.1039/d0sm02081h] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A new numerical framework based on Stokesian dynamics is used to study a shear-induced glass-to-crystal transition in suspensions of clay-like anisotropically charged platelets. The structures obtained in quiescent conditions are in agreement with previous Monte Carlo results: a liquid phase at very short interaction range (high salt concentration), phase separation and a gel without large scale density fluctuations at intermediate interaction ranges, and glassy states at very large interaction ranges. When initially glassy suspensions are sheared, hydrodynamic torques first rotate platelets so they can reach a transient quasi-nematic disordered state. These orientational correlations permit to unlock translational degrees of freedom and the platelets then form strings aligned with the velocity direction and hexagonally packed in the gradient-vorticity plane. Under steady shear, platelet orientations are correlated but the system is not nematic. After flow cessation and relaxation in quiescent conditions, positional and orientational order are further improved as the platelet suspension experiences a transition to a nematic hexagonal crystal. Energy calculations and the existence of residual stress anisotropy after relaxation show that this final structure is not an equilibrium state but rather a new ordered, arrested state. The transient, nematic, disordered state induced by shear immediately after startup and unlocking translational degrees of freedom is thought to be an initial step that may be generic for other suspensions of strongly anisotropic colloids with important translation-orientation coupling induced by long-range interactions.
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Affiliation(s)
- Vincent Labalette
- Laboratoire de Génie Chimique, Université de Toulouse, CNRS, INPT, UPS, Toulouse, France.
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Synthesis and applications of anisotropic nanoparticles with precisely defined dimensions. Nat Rev Chem 2020; 5:21-45. [PMID: 37118104 DOI: 10.1038/s41570-020-00232-7] [Citation(s) in RCA: 97] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/12/2020] [Indexed: 02/07/2023]
Abstract
Shape and size play powerful roles in determining the properties of a material; controlling these aspects with precision is therefore an important, fundamental goal of the chemical sciences. In particular, the introduction of shape anisotropy at the nanoscale has emerged as a potent way to access new properties and functionality, enabling the exploration of complex nanomaterials across a range of applications. Recent advances in DNA and protein nanotechnology, inorganic crystallization techniques, and precision polymer self-assembly are now enabling unprecedented control over the synthesis of anisotropic nanoparticles with a variety of shapes, encompassing one-dimensional rods, dumbbells and wires, two-dimensional and three-dimensional platelets, rings, polyhedra, stars, and more. This has, in turn, enabled much progress to be made in our understanding of how anisotropy and particle dimensions can be tuned to produce materials with unique and optimized properties. In this Review, we bring these recent developments together to critically appraise the different methods for the bottom-up synthesis of anisotropic nanoparticles enabling exquisite control over morphology and dimensions. We highlight the unique properties of these materials in arenas as diverse as electron transport and biological processing, illustrating how they can be leveraged to produce devices and materials with otherwise inaccessible functionality. By making size and shape our focus, we aim to identify potential synergies between different disciplines and produce a road map for future research in this crucial area.
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El Rifaii K, Wensink HH, Bizien T, Gabriel JCP, Michot L, Davidson P. Destabilization of the Nematic Phase of Clay Nanosheet Suspensions by Polymer Adsorption. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:12563-12571. [PMID: 33050693 DOI: 10.1021/acs.langmuir.0c02084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Complex aqueous mixtures comprised of swelling clays and hydrosoluble polymers naturally occur in soils and play a major role in pedogenesis. They are also very often used for formulating oil-well drilling fluids, paints, and personal-care products. The suspensions of some natural clays, thanks to their large nanoparticle aspect ratio, spontaneously form nematic liquid-crystalline phases where the particles align parallel to each other, which affects their flow properties. We observed that adding small amounts of hydrosoluble polymers to these clay suspensions destabilizes the nematic phase with respect to the isotropic (disordered) phase. The polymers that we used (poly(ethylene oxide) and dextran) were too small to adopt particle-bridging conformations and small-angle X-ray scattering experiments showed that the structure of the nematic phase is not altered by polymer doping. However, the adsorption isotherm shows that the macromolecules adsorb onto the clay nanosheets, effectively coating them with a polymer layer. Our extension of Onsager's theory for polymer-coated platelets properly captures the experimental phase diagram and shows how the nematic phase destabilization can be due to the polymer adsorbing more on the platelet faces than at the rim. Because the flow properties of the nematic phase are very different from those of the isotropic phase, the presence or absence of the former phase is an important factor to be determined and considered to explain the rheological behavior of these complex systems.
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Affiliation(s)
- Karin El Rifaii
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France
| | - Henricus H Wensink
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France
| | - Thomas Bizien
- SWING beamline, SOLEIL Synchrotron, 91192 Gif-sur-Yvette, France
| | | | - Laurent Michot
- Laboratory of Physical Chemistry of Electrolytes and Interfacial Nanosystems (PHENIX), Sorbonne Universite', CNRS, 75005 Paris, France
| | - Patrick Davidson
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France
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Affiliation(s)
- Michael P. Allen
- Department of Physics, University of Warwick, Coventry, UK
- H. H. Wills Physics Laboratory, Royal Fort, Bristol, UK
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Wensink HH. Frank elasticity of composite colloidal nematics with anti-nematic order. SOFT MATTER 2018; 14:8935-8944. [PMID: 30379187 DOI: 10.1039/c8sm01442f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Mixing colloid shapes with distinctly different anisotropy generates composite nematics in which the order of the individual components can be fundamentally different. In colloidal rod-disk mixtures or hybrid nematics composed of anisotropic colloids immersed in a thermotropic liquid crystal, one of the components may adopt so-called anti-nematic order while the other exhibits conventional nematic alignment. Focussing on simple models for hard rods and disks, we employ Onsager-Straley's second-virial theory to derive scaling expressions for the elastic moduli of rods and disks in both nematic and anti-nematic configurations and identify their explicit dependence on particle concentration and shape. We demonstrate that the splay, bend and twist elasticity of anti-nematically ordered particles scale logarithmically with the degree of anti-nematic order, with the bend-splay ratio for anti-nematic discotic nematics being far greater than for conventional nematic systems. The impact of surface anchoring on the elastic properties of hybrid nematics will also be discussed in detail. We further demonstrate that the elasticity of mixed uniaxial rod-disk nematics depends exquisitely on the shape of the components and we provide simple scaling expressions that could help engineer the elastic properties of composite nematic liquid crystals.
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Affiliation(s)
- H H Wensink
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France.
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Nehring A, Shendruk TN, de Haan HW. Morphology of depletant-induced erythrocyte aggregates. SOFT MATTER 2018; 14:8160-8171. [PMID: 30260361 DOI: 10.1039/c8sm01026a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Red blood cells suspended in quiescent plasma tend to aggregate into multicellular assemblages, including linearly stacked columnar rouleaux, which can reversibly form more complex clusters or branching networks. While these aggregates play an essential role in establishing hemorheological and pathological properties, the biophysics behind their self-assembly into dynamic mesoscopic structures remains under-explored. We employ coarse-grained molecular simulations to model low-hematocrit erythrocytes subject to short-range implicit depletion forces, and demonstrate not only that depletion interactions are sufficient to account for a sudden dispersion-aggregate transition, but also that the volume fraction of depletant macromolecules controls small aggregate morphology. We observe a sudden transition from a dispersion to a linear column rouleau, followed by a slow emergence of disorderly amorphous clusters of many short rouleaux at larger volume fractions. This work demonstrates how discocyte topology and short-range, non-specific, physical interactions are sufficient to self-assemble erythrocytes into various aggregate structures, with markedly different morphologies and biomedical consequences.
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Affiliation(s)
- Austin Nehring
- University of Ontario Institute of Technology, Faculty of Science, 2000 Simcoe Street North, Oshawa, Ontario L1H 7K4, Canada.
| | - Tyler N Shendruk
- Center for Studies in Physics and Biology, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Hendrick W de Haan
- University of Ontario Institute of Technology, Faculty of Science, 2000 Simcoe Street North, Oshawa, Ontario L1H 7K4, Canada.
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Abstract
The phase diagram of colloidal suspensions of electrically charged nanosheets, such as clays, despite their many industrial uses, is not yet understood either experimentally or theoretically. When the nanosheet diameter is very large (∼100 nm to 1 µm), it is quite challenging to distinguish the lamellar liquid-crystalline phase from a nematic phase with strong stacking local order, often called "columnar" nematic. We show here that newly upgraded small-angle X-ray scattering beamlines at synchrotron radiation facilities provide high-resolution measurements which allow us to identify both phases unambiguously, provided that single domains can be obtained. We investigated dilute aqueous suspensions of synthetic Sb3P2O143- nanosheets that self-organize into two distinct liquid-crystalline phases, sometimes coexisting in the same sample. Close examination of their X-ray reflection profiles in the directions perpendicular to the director demonstrates that these two mesophases are a columnar nematic and a lamellar phase. In the latter, the domain size reaches up to ∼20 µm, which means that each layer is made of >600 nanosheets. Because the lamellar phase was only rarely predicted in suspensions of charged disks, our results show that these systems should be revisited by theory or simulations. The unexpected stability of the lamellar phase also suggests that the rims and faces of Sb3P2O143- nanosheets may have different properties, giving them a patchy particle character.
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Bartsch H, Bier M, Dietrich S. Smectic phases in ionic liquid crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:464002. [PMID: 28972199 DOI: 10.1088/1361-648x/aa9090] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ionic liquid crystals (ILCs) are anisotropic mesogenic molecules which carry charges and therefore combine properties of liquid crystals, e.g. the formation of mesophases, and of ionic liquids, such as low melting temperatures and tiny triple-point pressures. Previous density functional calculations have revealed that the phase behavior of ILCs is strongly affected by their molecular properties, i.e. their aspect ratio, the loci of the charges, and their interaction strengths. Here, we report new findings concerning the phase behavior of ILCs as obtained by density functional theory and Monte Carlo simulations. The most important result is the occurrence of a novel, wide smectic-A phase [Formula: see text], at low temperature, the layer spacing of which is larger than that of the ordinary high-temperature smectic-A phase [Formula: see text]. Unlike the ordinary smectic S A phase, the structure of the [Formula: see text] phase consists of alternating layers of particles oriented parallel to the layer normal and oriented perpendicular to it.
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Affiliation(s)
- Hendrik Bartsch
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany. Institut für Theoretische Physik IV, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
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Wensink HH, Avendaño C. Empty smectic liquid crystals of hard nanorings: Insights from a second-virial theory. Phys Rev E 2016; 94:062704. [PMID: 28085407 DOI: 10.1103/physreve.94.062704] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Indexed: 06/06/2023]
Abstract
Inspired by recent simulations on highly open liquid crystalline structures formed by rigid planar nanorings, we present a simple theoretical framework explaining the prevalence of smectic over nematic ordering in systems of ring-shaped objects. The key part of our study is a calculation of the excluded volume of such nonconvex particles in the limit of vanishing thickness to diameter ratio. Using a simple stability analysis we then show that dilute systems of ring-shaped particles have a strong propensity to order into smectic structures with an unusual antinematic order while solid disks of the same dimensions exhibit nematic order. Since our model rings have zero internal volume, these smectic structures are essentially empty, resembling the strongly porous structures found in simulation. We argue that the antinematic intralamellar order of the rings plays an essential role in stabilizing these smectic structures.
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Affiliation(s)
- H H Wensink
- Laboratoire de Physique des Solides, Université Paris-Sud & CNRS, UMR 8502, 91405 Orsay, France
| | - C Avendaño
- School of Chemical Engineering and Analytical Science, University of Manchester, Sackville Street, Manchester M13 9PL, United Kingdom
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