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Nanoconfinement-induced structures in chiral liquid crystals.

Melle M, Theile M, Hall CK, Schoen M - Int J Mol Sci (2013)

Bottom Line: We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality.At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality.More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II.

View Article: PubMed Central - PubMed

Affiliation: Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Straße des 17. Juni 135, Berlin 10623, Germany. michael.melle@gmx.net

ABSTRACT
We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase.

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Related in: MedlinePlus

Components nx (z) as a function of position along the z-axis for () ɛ3 = 0.14 (cf., Figure 3) and () ɛ3 = 0.90. In addition, the local nematic order parameter, λ (z), is shown for ɛ3 = 0.14 () and ɛ3 = 0.90 (). For ɛ3 = 0.90, mesogens are directionally anchored at both substrate surfaces [see Equation (10a)], because the planar alignment leads to a decrease of the order, as explained in the text and, therefore, destabilizes the structure. Here, sz is chosen to coincide roughly with 3p. For ɛ3 = 0.14, hybrid anchoring is employed [see Equations (10)], as already explained.
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f5-ijms-14-17584: Components nx (z) as a function of position along the z-axis for () ɛ3 = 0.14 (cf., Figure 3) and () ɛ3 = 0.90. In addition, the local nematic order parameter, λ (z), is shown for ɛ3 = 0.14 () and ɛ3 = 0.90 (). For ɛ3 = 0.90, mesogens are directionally anchored at both substrate surfaces [see Equation (10a)], because the planar alignment leads to a decrease of the order, as explained in the text and, therefore, destabilizes the structure. Here, sz is chosen to coincide roughly with 3p. For ɛ3 = 0.14, hybrid anchoring is employed [see Equations (10)], as already explained.

Mentions: Moreover, one notices that the local nematic order decreases with enhanced chirality. This can be seen from plots in Figure 5, where λ (z) around z = 0 and for ɛ3 = 0.90 decays to a value characteristic of an isotropic phase. However, the liquid crystal is not isotropic locally, but does indeed form a highly structured, morphologically distinct phase under these conditions, as we shall demonstrate shortly.


Nanoconfinement-induced structures in chiral liquid crystals.

Melle M, Theile M, Hall CK, Schoen M - Int J Mol Sci (2013)

Components nx (z) as a function of position along the z-axis for () ɛ3 = 0.14 (cf., Figure 3) and () ɛ3 = 0.90. In addition, the local nematic order parameter, λ (z), is shown for ɛ3 = 0.14 () and ɛ3 = 0.90 (). For ɛ3 = 0.90, mesogens are directionally anchored at both substrate surfaces [see Equation (10a)], because the planar alignment leads to a decrease of the order, as explained in the text and, therefore, destabilizes the structure. Here, sz is chosen to coincide roughly with 3p. For ɛ3 = 0.14, hybrid anchoring is employed [see Equations (10)], as already explained.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3794743&req=5

f5-ijms-14-17584: Components nx (z) as a function of position along the z-axis for () ɛ3 = 0.14 (cf., Figure 3) and () ɛ3 = 0.90. In addition, the local nematic order parameter, λ (z), is shown for ɛ3 = 0.14 () and ɛ3 = 0.90 (). For ɛ3 = 0.90, mesogens are directionally anchored at both substrate surfaces [see Equation (10a)], because the planar alignment leads to a decrease of the order, as explained in the text and, therefore, destabilizes the structure. Here, sz is chosen to coincide roughly with 3p. For ɛ3 = 0.14, hybrid anchoring is employed [see Equations (10)], as already explained.
Mentions: Moreover, one notices that the local nematic order decreases with enhanced chirality. This can be seen from plots in Figure 5, where λ (z) around z = 0 and for ɛ3 = 0.90 decays to a value characteristic of an isotropic phase. However, the liquid crystal is not isotropic locally, but does indeed form a highly structured, morphologically distinct phase under these conditions, as we shall demonstrate shortly.

Bottom Line: We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality.At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality.More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II.

View Article: PubMed Central - PubMed

Affiliation: Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Straße des 17. Juni 135, Berlin 10623, Germany. michael.melle@gmx.net

ABSTRACT
We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase.

Show MeSH
Related in: MedlinePlus