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Zigzag line defects and manipulation of colloids in a nematic liquid crystal in microwrinkle grooves.

Ohzono T, Fukuda J - Nat Commun (2012)

Bottom Line: This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces.The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects.Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects.

View Article: PubMed Central - PubMed

Affiliation: Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Japan. ohzono-takuya@aist.go.jp

ABSTRACT
Spatially confined liquid crystals exhibit non-uniform alignment, often accompanied by self-organised topological defects of non-trivial shape in response to imposed boundary conditions and geometry. Here we show that a nematic liquid crystal, when confined in a sinusoidal microwrinkle groove, exhibits a new periodic arrangement of twist deformations and a zigzag line defect. This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces. The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects. Moreover, the kinks in the zigzag defects can trap small particles, which may afford a new method for manipulation of colloids. Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects.

No MeSH data available.


Related in: MedlinePlus

Trapped silica beads at the domain boundaries of a periodic domain structure.(a) Schematic of the trapped beads at the kinks of the zigzag disclination line, or domain boundaries of the periodic domain structure. (b,c) Optical images of the periodic domain structure with two trapped silica beads at the disclination line kinks. The arrows indicate the positions of the beads. In (b), a tint plate (S) was used. The colour changes depending on the angle between the local n and the direction of S; blue (orange) colour suggests that n is parallel (normal) to the direction of S. (d) Optical image of the released silica beads just after the transition from a nematic to an isotropic phase (see also Supplementary Movie 1). The disclination line disappears and the beads are free to move in the isotropic liquid filament. The same part of the system is pictured in (b,c and d). Scale bar is 15 μm.
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f3: Trapped silica beads at the domain boundaries of a periodic domain structure.(a) Schematic of the trapped beads at the kinks of the zigzag disclination line, or domain boundaries of the periodic domain structure. (b,c) Optical images of the periodic domain structure with two trapped silica beads at the disclination line kinks. The arrows indicate the positions of the beads. In (b), a tint plate (S) was used. The colour changes depending on the angle between the local n and the direction of S; blue (orange) colour suggests that n is parallel (normal) to the direction of S. (d) Optical image of the released silica beads just after the transition from a nematic to an isotropic phase (see also Supplementary Movie 1). The disclination line disappears and the beads are free to move in the isotropic liquid filament. The same part of the system is pictured in (b,c and d). Scale bar is 15 μm.

Mentions: Disclination lines can trap small particles to reduce the total elastic energy of the system262728; the particles remove the energetically costly disclination cores. We indeed observed silica beads trapped at the disclination line at which the strongest elastic deformation is likely (Fig. 3). It should be noted that the particles cannot move freely along the disclination line, but are trapped selectively at its kinks. The kinks in the disclination line are presumably more energetically unfavourable than the straight parts, which result in stronger binding of beads at the kinks. In addition, when the system is heated to the isotropic phase, the beads are no longer trapped and show random motion (Supplementary Movie 1). Our observation demonstrates that topological defects can have an active role in the control of colloidal assembly in LCs, whereas in usual LC colloids, topological defects are formed passively in response to colloid-surface anchoring19. Zigzag disclination lines can thus provide a novel way of manipulating colloidal particles.


Zigzag line defects and manipulation of colloids in a nematic liquid crystal in microwrinkle grooves.

Ohzono T, Fukuda J - Nat Commun (2012)

Trapped silica beads at the domain boundaries of a periodic domain structure.(a) Schematic of the trapped beads at the kinks of the zigzag disclination line, or domain boundaries of the periodic domain structure. (b,c) Optical images of the periodic domain structure with two trapped silica beads at the disclination line kinks. The arrows indicate the positions of the beads. In (b), a tint plate (S) was used. The colour changes depending on the angle between the local n and the direction of S; blue (orange) colour suggests that n is parallel (normal) to the direction of S. (d) Optical image of the released silica beads just after the transition from a nematic to an isotropic phase (see also Supplementary Movie 1). The disclination line disappears and the beads are free to move in the isotropic liquid filament. The same part of the system is pictured in (b,c and d). Scale bar is 15 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3293426&req=5

f3: Trapped silica beads at the domain boundaries of a periodic domain structure.(a) Schematic of the trapped beads at the kinks of the zigzag disclination line, or domain boundaries of the periodic domain structure. (b,c) Optical images of the periodic domain structure with two trapped silica beads at the disclination line kinks. The arrows indicate the positions of the beads. In (b), a tint plate (S) was used. The colour changes depending on the angle between the local n and the direction of S; blue (orange) colour suggests that n is parallel (normal) to the direction of S. (d) Optical image of the released silica beads just after the transition from a nematic to an isotropic phase (see also Supplementary Movie 1). The disclination line disappears and the beads are free to move in the isotropic liquid filament. The same part of the system is pictured in (b,c and d). Scale bar is 15 μm.
Mentions: Disclination lines can trap small particles to reduce the total elastic energy of the system262728; the particles remove the energetically costly disclination cores. We indeed observed silica beads trapped at the disclination line at which the strongest elastic deformation is likely (Fig. 3). It should be noted that the particles cannot move freely along the disclination line, but are trapped selectively at its kinks. The kinks in the disclination line are presumably more energetically unfavourable than the straight parts, which result in stronger binding of beads at the kinks. In addition, when the system is heated to the isotropic phase, the beads are no longer trapped and show random motion (Supplementary Movie 1). Our observation demonstrates that topological defects can have an active role in the control of colloidal assembly in LCs, whereas in usual LC colloids, topological defects are formed passively in response to colloid-surface anchoring19. Zigzag disclination lines can thus provide a novel way of manipulating colloidal particles.

Bottom Line: This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces.The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects.Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects.

View Article: PubMed Central - PubMed

Affiliation: Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Japan. ohzono-takuya@aist.go.jp

ABSTRACT
Spatially confined liquid crystals exhibit non-uniform alignment, often accompanied by self-organised topological defects of non-trivial shape in response to imposed boundary conditions and geometry. Here we show that a nematic liquid crystal, when confined in a sinusoidal microwrinkle groove, exhibits a new periodic arrangement of twist deformations and a zigzag line defect. This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces. The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects. Moreover, the kinks in the zigzag defects can trap small particles, which may afford a new method for manipulation of colloids. Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects.

No MeSH data available.


Related in: MedlinePlus