Imaging the Azimuthal Tilt Order in Monolayers by Liquid Crystal Optical Amplification

Fang, Jiyu; Gehlert, U.; Shashidar, R.; Knobler, Charles M.

doi:10.1021/la9812929

Cited by 38 publications

(35 citation statements)

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“…In ref. 22, we showed that the variation of the molecular tilt direction in the Langmuir monolayer of 1-monopalmitoyl-rac-glycerol can induce an azimuthal orientation in nematic liquid-crystal layers. After the liquid-crystal optical amplification, the tilted textures in the monolayer can be easily visualized with a polarizing optical microscope.…”

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confidence: 87%

“…In recent years, there has been an increased interest in developing an imaging technique based on liquid-crystal optical amplification for studying the structures and physical properties of organic and biological interfaces (21)(22)(23)(24)(25). It has been demonstrated that liquid crystals can map differences in the spatial orientation of terminal groups in self-assembled monolayers (SAMs) formed from alkanethiols that differ by single methylene (21).…”

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confidence: 99%

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Liquid-crystal imaging of molecular-tilt ordering in self-assembled lipid tubules

Zhao

Mahajan

Lü

et al. 2005

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

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Self-assembled cylindrical tubules of chiral phospholipids are interesting supramolecular structures. Understanding the moleculartilt order is a key step in controlling the size and shape of the tubules and designing new functional materials. The current theories based on the chiral interactions, coupled with molecular tilt, have predicted that the tubules could have both uniform and modulated tilt states. Here, we image the molecular-tilt order in the self-assembled tubules of a chiral phospholipid by using liquid crystals as an optical amplification probe. We demonstrate that the organization of the molecular-tilt azimuth in the lipid tubules can induce an azimuthal orientation in the liquid crystals. Both uniform and modulated tilt states of the lipid tubules are observed after liquid-crystal optical amplification.liquid-crystal amplification ͉ molecular ordering ͉ self-assembly ͉ optical amplification ͉ supramolecular structure T he self-assembled cylindrical tubules have attracted considerable attention because of their interesting supramolecular structures and technological applications (1, 2). It has been found that a variety of amphiphilies, including alkylaldonamides (3), diacetylenic phospholipids (4, 5), amino acid-based surfactants (6, 7), and multicomponent mixtures in bile (8, 9), selfassemble into cylindrical tubules in solutions. Recently, advances have been made in controlling the sizes and shapes of tubules by adjusting the chemical compositions and the conditions under which self-assembly occurs (10-16).Theoretical models based on the chiral interactions, coupled with molecular tilt, have been used to explain the formation of the cylindrical tubules (17)(18)(19). In these models, the chiral molecules do not pack parallel to their neighbors but, rather, at a nonzero angle with respect to their neighbors. This chiral packing causes the twisting of a bilayer stripe, which leads to the formation of cylindrical tubules. The model by Selinger et al. (19) suggests that the tubules can have both uniform and modulated tilt states. In the uniform tilt state, the tubule has a constant orientation of the molecule tilt with respect to the equator of the cylinder (Fig. 1a). In the modulated tilt state, the tubule has a periodic modulated structure by helical stripes in the molecular tilted direction winding around the cylinder. The direction of the molecular tilt smoothly varies across the stripes and jumps at the edges of the stripes (Fig. 1b). These stripes in the tubules are suggested to be analogous to the tilted stripes seen in the Langmuir monolayers (20) but in a cylindrical rather than a planar geometry. To our knowledge, there has been no experimental test of the theoretical predictions because of the difficulty in probing the local direction of the molecular tilt in the tubules.In recent years, there has been an increased interest in developing an imaging technique based on liquid-crystal optical amplification for studying the structures and physical properties of organic and biological interfac...

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confidence: 87%

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confidence: 99%

Liquid-crystal imaging of molecular-tilt ordering in self-assembled lipid tubules

Zhao

Mahajan

Lü

et al. 2005

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

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“…Thus, optical properties of the LC can be used as a tool to investigate molecular order in the interfacial layer. 6 Anchoring orients the LC director at the boundary of interest and is defined by two angles: zenithal and azimuthal ( Figure 1). 7 The zenithal angle may be planar (director aligned parallel to the interface), homeotropic (director aligned perpendicular to the interface), or tilted (director aligned at an intermediate angle).…”

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confidence: 99%

Fatty-Acid Monolayers at the Nematic/Water Interface: Phases and Liquid-Crystal Alignment

Price

Schwartz

2007

J. Phys. Chem. B

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The two-dimensional (2D) phases of fatty-acid monolayers (hexadecanoic, octadecanoic, eicosanoic, and docosanoic acids) have been studied at the interface of a nematic liquid crystal (LC) and water. When observed between crossed polarizers, the LC responds to monolayer structure owing to mesoscopic alignment of the LC by the adsorbed molecules. Similar to Langmuir monolayers at the air/water interface, the adsorbed monolayer at the nematic/water interface displays distinct thermodynamic phases. Observed are a 2D gas, isotropic liquid, and two condensed mesophases, each with a characteristic anchoring of the LC zenithal tilt and azimuth. By varying the monolayer temperature and surface concentration we observe reversible first-order phase transitions from vapor to liquid and from liquid to condensed. A temperature-dependent transition between two condensed phases appears to be a reversible swiveling transition in the tilt azimuth of the monolayer. Similar to monolayers at the air/water interface, the temperature of the gas/liquid/condensed triple-point temperature increased by about 10 degrees C for a two methylene group increase in chain length. However, the absolute value of the triple-point temperatures are depressed by about 40 degrees C compared to those of analogous monolayers at the air/water interface. We also observe a direct influence by the LC layer on the mesoscopic and macroscopic structure of the monolayer by analyzing the shapes and internal textures of gas domains in coexistence with a 2D liquid. An effective anisotropic line tension arises from elastic forces owing to deformation of the nematic director across phase boundaries. This results in the deformation of the domain from circular to elongated, with a distinct singularity. The LC elastic energy also gives rise to transition zones displaying mesoscopic realignment of the director tilt or azimuth between adjacent regions with a sudden change in anchoring.

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“…These films are previously self-assembled at the air/water interface [18], where they organize into isolated sub-millimeter circular islands featuring polar nematic order with the elongated molecules anchored at a fixed angle of the interface normal (~ 45º), and a tilt orientation tangential to the circular boundary (s = +1, c = π/2), which results in a selectable orientational chirality [19]. In contact with the LB-coated glass substrate, LC molecules follow the local in-plane orientation of the amphiphilic molecules in the monolayer [20]. This procedure, in which LC molecules are aligned by self-assembled patterns featuring a well-defined and robust tilt-orientational order in a monolayer of uniform thickness, is in contrast to other patterning techniques based on mechanical [21] or optical [22] modification of a polymer layer, which lacks a similar degree of order.…”

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Healing of Defects at the Interface of Nematic Liquid Crystals and Structured Langmuir-Blodgett Monolayers

et al. 2011

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Imaging the Azimuthal Tilt Order in Monolayers by Liquid Crystal Optical Amplification

Cited by 38 publications

References 20 publications

Liquid-crystal imaging of molecular-tilt ordering in self-assembled lipid tubules

Liquid-crystal imaging of molecular-tilt ordering in self-assembled lipid tubules

Fatty-Acid Monolayers at the Nematic/Water Interface: Phases and Liquid-Crystal Alignment

Healing of Defects at the Interface of Nematic Liquid Crystals and Structured Langmuir-Blodgett Monolayers

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