Shape anisotropy and ordered phases in reversibly assembling lyotropic systems

Taylor, Mark P.; Herzfeld, Judith

doi:10.1103/physreva.43.1892

Cited by 84 publications

(92 citation statements)

References 75 publications

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“…Physical properties of LCLCs and the phase transition temperatures are expected to be dependent on ionic content of the solution. Ionic additives might modify both the intra-(interactions between the molecules belonging to the same aggregate) and inter-columnar interactions, thus altering electrostatic forces between the charged groups at the lateral surfaces of aggregates [10,[24][25][26]]. We conclude that the salt additives studied by us can be divided into three groups.…”

Section: Phase Behaviourmentioning

confidence: 98%

Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives

Boiko¹,

Vasyuta²,

Semenyshyn³

et al. 2008

Ukr. J. Phys. Opt.

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We investigate influence of different ionic additives on the phase behaviour and scalar order parameter of lyotropic chromonic nematic liquid crystals formed by the molecules representing derivatives of indanthrone. KI, (NH 4 ) 2 SO 4 and NaCl salts increase biphasic nematic region on the temperature-concentration phase diagram, whereas the scalar orientational order parameter is hardly sensitive to their presence. We suggest that these changes are attributed to increase in the aggregate length and polydispersity of the latter, while the interaction between aggregates remains unaffected. The Na 2 SO 4 salt lowers anomalously the measured value of the scalar order parameter to 0.42, for which the nematic phase should not exist. We address this anomaly to modification of the shape of chromonic aggregates due to growing of side chains within the rod-like aggregates. The NH 4 Cl salt does not affect the phase diagram and the scalar order parameter of Blue 250 chromonematic.

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Section: Phase Behaviourmentioning

confidence: 98%

Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives

Boiko¹,

Vasyuta²,

Semenyshyn³

et al. 2008

Ukr. J. Phys. Opt.

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“…[23]. [28][29][30][31][32][33] More recently, an increasing number of molecular dynamics simulations on surfactant micelles has been published. [34][35][36][37][38][39][40][41][42] However, with this method one is usually restricted to rather small micelles, that is, to micelles with aggregation numbers below or close to the maximum value for a spherical shape.…”

Section: Introductionmentioning

confidence: 99%

Bending Energetics of Tablet‐Shaped Micelles: A Novel Approach to Rationalize Micellar Systems

Bergström

2007

ChemPhysChem

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A novel approach to rationalize micellar systems is expounded in which the structural behavior of tablet-shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H0), bending rigidity (k(c)), and saddle-splay constant (k(c)). As a result, experimentally accessible micellar properties, such as aggregation number, length-to-width ratio, and polydispersity, may be related to the different bending elasticity constants. It is demonstrated that discrete micelles or connected cylinders form when H0 > 1/4xi, where xi is the thickness of a surfactant monolayer, whereas various bilayer structures are expected to predominate when H0 < 1/4xi. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet-shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critical surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydisperse elongated micelles (large length-to-width ratio) form as the bending rigidity is lowered, approaching the critical point at k(c) = 0, whereas monodisperse globular micelles (small length-to-width ratio) are expected to be present at large k(c) values. The spontaneous curvature mainly determines the width of tablet-shaped or ribbonlike micelles, or the radius of disklike micelles, whereas the saddle-splay constant primarily influences the size but not the shape of the micelles.

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“…The physical picture then corresponds to higher concentrations having shorter aggregates but a larger number of them, whereas lower concentrations have longer but fewer aggregates at the transition temperature. A more comprehensive theory can capture the details regarding the influence of temperature and polydispersity of the aggregates in affecting the nature of the phase transition (34,(46)(47)(48), but we believe the essential physical picture is qualitatively captured by the simple model we provide.…”

Section: Bmentioning

confidence: 99%

Using chiral tactoids as optical probes to study the aggregation behavior of chromonics

Nayani

Chang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Tactoids are nuclei of an orientationally ordered nematic phase that emerge upon cooling the isotropic phase. In addition to providing a natural setting for exploring chromonics under confinement, we show that tactoids can also serve as optical probes to delineate the role of temperature and concentration in the aggregation behavior of chromonics. For high concentrations, we observe the commonly reported elongated bipolar tactoids. As the concentration is lowered, breaking of achiral symmetry in the director configuration is observed with a predominance of twisted bipolar tactoids. On further reduction of concentration, a remarkable transformation of the director configuration occurs, wherein it conforms to a unique splay-minimizing configuration. Based on a simple model, we arrive at an interesting result that lower concentrations have longer aggregates at the same reduced temperature. Hence, the splay deformation that scales linearly with the aggregate length becomes prohibitive for lower concentrations and is relieved via twist and bend deformations in this unique configuration. Raman scattering measurements of the order parameters independently verify the trend in aggregate lengths and provide a physical picture of the nematic-biphasic transition.chirality | self-assembly | chromonics | tactoids | phase transitions W hen an isotropic phase of a lyotropic system undergoes a phase transition to an ordered nematic phase, the pathway is usually mediated through spindle-shaped droplets called tactoids. Observation and analysis of tactoids have been an integral part of the investigations on liquid crystals, including some of the earliest experiments that motivated the seminal theory of Onsager (1-3). Tactoids also provide a natural setting to study nematics under confinement (4-6). Hence, they are an attractive setting as a testbed for fundamental research as well as being relevant to technological applications. This has driven the experimental investigation of tactoids in a host of materials, including dispersions of viruses (1, 3), proteins (7), inorganic platelets (8), and lyotropic chromonic liquid crystals (LCLCs) (4).The director configuration in the tactoids is dictated by the individual contribution of the elastic constants, splay (K11), twist (K22), and bend (K33) to the Frank free energy (4, 9). Historically, tactoids of lyotropic nematic liquid crystals have been found to have an elongated shape and adopt a bipolar configuration with the director following the meridional lines (1,8,9). Only recently has a twisted-bipolar director configuration been experimentally realized for a LCLC system when it was crowded with polyethylene glycol (PEG) (4). Twisted-bipolar tactoids of cellulose nanocrystals have also been demonstrated recently (10). The emergence of chirality in achiral liquid crystals has fueled the curiosity of scientists ever since their discovery (11, 12). There have been a host of technological applications that take advantage of chiral configurations of confined liquid crystals (13,14). In thi...

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Shape anisotropy and ordered phases in reversibly assembling lyotropic systems

Cited by 84 publications

References 75 publications

Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives

Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives

Bending Energetics of Tablet‐Shaped Micelles: A Novel Approach to Rationalize Micellar Systems

Using chiral tactoids as optical probes to study the aggregation behavior of chromonics

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