Hexagonal Order in Crystalline and Columnar Phases of Hard Rods

Grelet, Éric

doi:10.1103/physrevlett.100.168301

Cited by 93 publications

(125 citation statements)

References 52 publications

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“…In biological systems the organization of the cell is determined, among other things, by the packing of fibril-like particles (actin filaments, DNA) [1,2]. An example of the subtlety of packing phenomena is the plethora of liquid crystalline phases that can be found in arrangements of anisotropic particles by increasing concentration [3,4]. Confinement of liquid crystals adds to the complexity, since the interactions of the particles with the walls may lead to structures that compete with those formed in the bulk [5,6].…”

Section: Pacs Numbersmentioning

confidence: 99%

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

et al. 2012

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We study the nematic phase of rodlike fd -virus particles confined to channels with wedgestructured walls. Using laser scanning confocal microscopy we observe a splay-to-bend transition at the single particle level as a function of the wedge opening angle. Lattice Boltzmann simulations reveal the underlying origin of the transition and its dependence on nematic elasticity and wedge geometry. Our combined work provides a simple method to obtain the splay-to-bend elasticity ratios and offers a way to control the position of defects through the confining boundary conditions. PACS numbers:Packing and confinement problems emerge in fields ranging from biology to engineering. In biological systems the organization of the cell is determined, among other things, by the packing of fibril-like particles (actin filaments, DNA) [1,2]. An example of the subtlety of packing phenomena is the plethora of liquid crystalline phases that can be found in arrangements of anisotropic particles by increasing concentration [3,4]. Confinement of liquid crystals adds to the complexity, since the interactions of the particles with the walls may lead to structures that compete with those formed in the bulk [5,6]. Many of the next generation liquid crystal display devices exploit this interplay by using structured or patterned surfaces as an essential element of their design [7,8]. Very recently, the ordering at sawtoothed structures has been studied theoretically within a Landau-De Gennes framework [9,10], with a focus on the wetting behaviour. In this Letter, in a combined experimental and theoretical effort, we show the rich phenomenology that emerges when confining a nematic liquid crystal to a microfluidic channel with a wedge structured wall. We seek to disentangle how the wedge geometry and elasticity of the fd -virus' nematic phase determine the adopted deformation in the wedge. We introduce a new method for estimating elastic constants suitable to colloidal and biological systems, as an alternative to previous methods using magnetic fields [11] or light scattering [12]. Specifically, we determine the transition from a splay to a bend director field, with increasing wedge angle.We use the fd -virus, which is an excellent model liquid crystal system for both static and dynamic behaviour [13][14][15][16]. The virus' contour length and diameter are 0.88 µm and 6.6 nm, respectively. These dimensions allow for the 3D determination of the position and orientation of individual particles by means of laser scanning confocal microscopy (LSCM). Thus we obtain detailed mechanistic insights on a single particle level of the director field. Moreover, due to the relatively large size of the particles, we can study effects of wall structures that are, when translated to the scale of thermotropic liquid crystals, very small and inaccessible. The particles were grown following standard protocols [17] and dispersed in 20 mM tris buffer at pH 8.15 with 100 mM NaCl and 15% EtOH. The ethanol was added to prevent the growth of bacteria. The virus concent...

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Section: Pacs Numbersmentioning

confidence: 99%

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

et al. 2012

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“…We choose this potential to mimic the soft screened electrostatic repulsion between the charge-stabilized fd virus particles in the experiments of Grelet and collaborators. 42,43 To obtain the phase diagram of our particles, we run simulations in the isobaric-isothermal (NPT) ensemble at different pressures, starting from an AAA crystal initial configuration. We incrementally expand the system from the highest pressure, P * = 5.0, to the lowest one, P * = 1.0, where P * is related to the actual pressure of the system, P, by P * = Pσ 3 /k B T. In each step, we first slowly decrease the pressure in a short simulation run of 10 5 simulation steps and after that we carry out a NPT simulation at the final value of pressure with 6 × 10 6 time steps.…”

Section: Model and Simulation Methodsmentioning

confidence: 99%

Effect of bending flexibility on the phase behavior and dynamics of rods

Naderi

Schoot

2014

The Journal of Chemical Physics

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Articles you may be interested inThe phase behavior, structure, and dynamics of rodlike mesogens with various flexibility using dissipative particle dynamics simulation J. Chem. Phys. 133, 144911 (2010) Effect of bending flexibility on the phase behavior and dynamics of rods Saber Naderi 1,2,a) and Paul van der Schoot 1,3 We study by means of molecular and Brownian dynamics simulations the influence of bending flexibility on the phase behavior and dynamics of monodisperse hard filamentous particles with an aspect ratio of 8 and persistence lengths equal to 3 and 11 times the particle length. Although our particles are much shorter, the latter corresponds to the values for wild-type and mutant fd virus particles that have been subject of a recent experimental study, where the diffusion of these particles in the nematic and smectic-A phase was investigated by means of video fluorescence microscopy [E. Pouget, E. Grelet, and M. P. Lettinga, Phys. Rev. E 84, 041704 (2011)]. In agreement with theoretical predictions and simulations, we find that for the more flexible particles (shorter persistence length) the nematic (N) to smectic-A (Sm-A) phase transition shifts to larger values of the particle density. Interestingly, we find that for the more rigid particles (larger persistence length), the smectic layer-tolayer distance decreases monotonically with increasing density, whereas for the more flexible ones, it first increases, reaches a maximum and then decreases. For our more flexible particles, we find a smectic-B phase at sufficiently high densities. Moreover, in line with experimental observations and theoretical predictions, we find heterogeneous dynamics in the Sm-A phase, in which particles hop between the smectic layers. We compare the diffusion of our two types of particle at identical values of smectic order parameter, and find that flexibility does not change the diffusive behavior of particles along the director yet significantly slows down the diffusion perpendicular to it. In our simulations, the ratio of diffusion constants along and perpendicular to the director decreases just beyond the N-Sm-A phase transition for both our stiff and more flexible particles. © 2014 AIP Publishing LLC.

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“…I, optical textures obtained from experiments on the columnar phase formed by fd virus particles in water shows that this phase has a polydomain structure with grain boundaries [18]. From this optical texture, the size of these domains can be estimated to be of the order of 10 particle lengths.…”

Section: Domain Size Effectsmentioning

confidence: 99%

“…This potential mimics the soft screened electrostatic repulsion that acts between the charge-stabilized fd virus particles in the experiments of Grelet and collaborators [18,41]. In order to prevent the formation of a smectic phase in our simulations and to mimic the self-consistent field that particles experience in the hexagonal columnar phase, we apply an external potential to all the particles (beads).…”

Section: Model and Simulationsmentioning

confidence: 99%

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Collective stringlike motion of semiflexible filamentous particles in columnar liquid crystalline phases

Naderi

Schoot

2013

Phys. Rev. E

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We study, by means of Brownian dynamics simulations, heterogeneous dynamics in a dense columnar phase of monodisperse hard filamentous particles, and find that in a background of barely moving particles, some particles occasionally engage in a fast coherent string-type motion similar to what is observed in glassy states of isometric particles. This fast motion is triggered by the exchange of particles between two or more columns at different positions in the columns, which leads to sudden displacement of particles between these positions. The distribution of particle displacements shows a pronounced peak at one particle length. We perform our simulations with particles of different persistence lengths and find that for more flexible particles, the number of jump events increases. As the number of particles in the columns increases with system size for a given linear fraction of particles in the columns, the peak in the distribution becomes wider and, for sufficiently large systems, the peak disappears completely. This is associated with the increase in the magnitude of fluctuations in the motion of particles as the system size increases. Our simulation results explain recent experimental observations on single-particle motion in dense columnar phases in aqueous dispersions of filamentous virus particles.

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Hexagonal Order in Crystalline and Columnar Phases of Hard Rods

Cited by 93 publications

References 52 publications

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

Confinement Induced Splay-to-Bend Transition of Colloidal Rods

Effect of bending flexibility on the phase behavior and dynamics of rods

Collective stringlike motion of semiflexible filamentous particles in columnar liquid crystalline phases

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