Self-Diffusion and Molecular Order in Lyotropic Liquid Crystals

Blinc, R.; Easwaran, K. R. K.; Pirš, J.; Volfan, M.; Zupančić, I.

doi:10.1103/physrevlett.25.1327

Cited by 43 publications

(15 citation statements)

References 5 publications

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“…Recently, the dynamics of such self-assembled anisotropic media has been investigated in particular by the determination of selfdiffusion coefficients in different kinds of mesophases [4]. These measurements have been performed with experimental techniques probing the samples collectively (ensemble averaged), such as in nuclear magnetic resonance (NMR) for thermotropic [5] and amphiphilic [6] liquid crystals, and fluorescence recovery after photobleaching (FRAP) for lyotropic (colloidal) systems [7]. Only a few studies have been performed where dynamical phenomena are tracked at the scale of the single anisotropic particle [8,9].…”

Section: Introductionmentioning

confidence: 99%

Dynamical and structural insights into the smectic phase of rod-like particles

Grelet

Lettinga

Bier

et al. 2008

J. Phys.: Condens. Matter

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Abstract.Self-diffusion in a model system of rod-like particles is studied in the smectic (or lamellar) phase. The experimental system is formed by a colloidal suspension of filamentous fd virus particles, which allows the direct visualisation at the scale of the single particle of mass transport between the smectic layers. Self-diffusion takes place preferentially in the direction normal to the smectic layers and occurs in steps of one rod length, reminiscent of a hopping-type of transport. The probability density function is obtained experimentally at different times and is found to be in qualitative agreement with theoretical predictions based on a dynamical density functional theory.

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Section: Introductionmentioning

confidence: 99%

Dynamical and structural insights into the smectic phase of rod-like particles

Grelet

Lettinga

Bier

et al. 2008

J. Phys.: Condens. Matter

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“…Understanding of the particle mobility in the different liquid crystalline phases is more recent [4]. In experiments various methods have been applied to obtain the ensemble averaged selfdiffusion coefficients in thermotropic [5] and amphiphilic [6] liquid crystals, block copolymer [7] and colloidal systems [8]. Only a few studies have been done where dynamical phenomena are probed at the scale of a single anisotropic particle: the Brownian motion of an isolated colloidal ellipsoid in confined geometry [9] and the selfdiffusion in a nematic phase formed by rod-like viruses [10] represent two recent examples.…”

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Self-Diffusion of Rodlike Viruses through Smectic Layers

2007

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We report the direct visualization at the scale of single particles of mass transport between smectic layers, also called permeation, in a suspension of rod-like viruses. Self-diffusion takes place preferentially in the direction normal to the smectic layers, and occurs by quasi-quantized steps of one rod length. The diffusion rate corresponds with the rate calculated from the diffusion in the nematic state with a lamellar periodic ordering potential that is obtained experimentally.Since the pioneering work of Onsager on the entropy driven phase transition to a liquid crystalline state [1], the structure and the phase behavior of complex fluids containing anisotropic particles with hard core interactions has been a subject of considerable interest, both theoretically [2] and experimentally [3]. Understanding of the particle mobility in the different liquid crystalline phases is more recent [4]. In experiments various methods have been applied to obtain the ensemble averaged selfdiffusion coefficients in thermotropic [5] and amphiphilic [6] liquid crystals, block copolymer [7] and colloidal systems [8]. Only a few studies have been done where dynamical phenomena are probed at the scale of a single anisotropic particle: the Brownian motion of an isolated colloidal ellipsoid in confined geometry [9] and the selfdiffusion in a nematic phase formed by rod-like viruses [10] represent two recent examples. In the latter case, the diffusion parallel (D ) and perpendicular (D ⊥ ) to the average rod orientation (the director) has been measured, showing an increase of the ratio D /D ⊥ with particle concentration. Knowledge of the dynamics at the single particle level is fundamental for understanding the physics of mesophases with spatial order like the smectic (lamellar) phase of rod-like particles. In this mesophase the particle density is periodic in one dimension parallel to the long axis of the rods, while the interparticle correlations perpendicular to this axis are short-ranged (fluid-like order). For parallel diffusion to take place, the rods need to jump between adjacent smectic layers, overcoming an energy barrier related to the smectic order parameter [11]. This process of interlayer diffusion, or permeation, was first predicted by Helfrich [12]. In this Letter, we use video fluorescence microscopy to monitor the dynamics of individual labeled colloidal rods in the background of a smectic mesophase formed by identical but unlabeled rods. In this way we directly observe permeation of single rods in adjacent layers. As in the nematic phase, self-diffusion in a smectic phase is anisotropic: the diffusion through the smectic layers is shown here to be much faster than the diffusion within each liquid-like layer, i.e. D /D ⊥ ≫ 1, in contrast to thermotropic systems. Moreover, since the individual rod positions within the layer are monitored, the potential barrier for permeation is straightly determined for the first time. The permeation can then be . The layer spacing is L ≃ 0.9 µm. (b) Displacement of a given particle...

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“…19 In our case, it is assumed that not only the higher diffusion coefficient of water but also the reduction in surface tension leads to the diffusion of water between the smectic layers of the FLC. 25 The most important observation in these LC/water systems is the spatial variation of tilt angle observed in the nonconducting region of the sample where molecules were also observed to switch. This occurrence is here onwards termed as the spatially varying switching phenomenon.…”

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“…In order to fill the material into the cell, temperature of the oven was stabilized at 87°C, i.e., 4 -5°C below the nematic to isotropic phase transition where the self-diffusion of water into LC is maximum. 25 The system was then cooled at a very slow rate ͑0.25°C / min͒ just after the filling, so that homogeneous alignment was obtained, and then at fast rate ͑5°C/ min͒, so that water could not evaporate from the cell. Finally, the cell was sealed from all sides.…”

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confidence: 99%

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Electrically tunable spatially variable switching in ferroelectric liquid crystal/water system

Choudhary

Coondoo

Prakash

et al. 2009

Applied Physics Letters

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An unusual switching phenomenon in the region outside conducting patterned area in ferroelectric liquid crystal ͑FLC͒ containing about 1 -2 wt % of water has been observed. The presence of water in the studied heterogeneous system was confirmed by Fourier transform infrared spectroscopy. The observed optical studies have been emphasized on the "spatially variable switching" phenomenon of the molecules in the nonconducting region of the cell. The observed phenomenon is due to diffusion of water between the smectic layers of the FLC and the interaction of the curved electric field lines with the FLC molecules in the nonconducting region. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3126960͔Conjugation of water with amphiphilic and other organic compounds results in interesting optical and electrical properties of the system-the liquid crystal ͑LC͒ phase. 1-4 Lyotropic LCs, which are formed by addition of water to various amphiphilic materials, seem to play an important role in many biological systems including cell membranes. 5-7 The x-ray diffraction studies on the two most common phasesneat and middle-of lyotropic LCs have revealed that the neat phase is lamellar and the structure consists of alternate layers of the lyotropic mesogens and water. 1,5,8 Heterogeneous systems consisting of a LC and an immiscible liquid are of interest from both scientific perspective and for potential applications. The properties exhibited by such dispersions of chemically dissimilar phasesisotropic liquid and anisotropic LC host reflect an interesting microscopic structural organization due to the interactions between the constituents. 9,10 Several investigations have been carried out including studies on isotropic droplets in nematics, 11,12 nematic emulsions, 13,14 nematic LC/water interfaces, 15,16 etc. in such heterogeneous systems. The thermotropic LC hosts considered so far have been nematics, although little work has been reported on other mesophases like the smectics as well. [17][18][19] The common and most striking feature of the smectic phase is the existence of a layered structure. 10 The molecular centers are on average arranged in equidistant planes thus forming a stratified conformation rendering it both the long-range translational order plus local orientational order. The colloidal interaction between the interfaces of the constituents of a heterogeneous system plays a characteristic role in determining their unique properties. The interfacial surface tension ͑␥͒ at the interface between LC/air 1,20,21 and positive slope ͑d␥ / dT͒, T is the temperature, indicating the excess order at the interface LC/liquid 15,16,[22][23][24] are well reported.Based on these reports, it would be interesting to study the effect on various electro-optical properties of a smectic LC due to the diffusion of an isotropic liquid such as water, ethanol, etc. in between the smectic layers. With this objective, we in this letter, investigate the effect of mixing of an immiscible isotropic liquid ͑i.e., water͒ into the ferroelectri...

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Self-Diffusion and Molecular Order in Lyotropic Liquid Crystals

Cited by 43 publications

References 5 publications

Dynamical and structural insights into the smectic phase of rod-like particles

Dynamical and structural insights into the smectic phase of rod-like particles

Self-Diffusion of Rodlike Viruses through Smectic Layers

Electrically tunable spatially variable switching in ferroelectric liquid crystal/water system

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