Bend Elastic Constant in Ferroelectric Free Standing Films of Tilted Smectics

Najjar, R.; Galerne, Y.

doi:10.1080/10587250108023985

Cited by 5 publications

(3 citation statements)

References 5 publications

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“…A few reports have been made on the behavior of amphiphilic radicals on the Langmuir trough. − In all cases, the Langmuir films did not show the striking birefringent structures we observe here. Such nematic-like patterns are actually rather unusual in Langmuir films, and the published reports always involve liquid-crystalline materials. ,, Similar structures have been obtained more frequently in surface-induced films, free-standing films (although with artificial means in this case − ), hybrid films, and also with LC materials. Tabe et al describe similar looking Schlieren textures in a Langmuir film obtained with a smectic C compound …”

Section: Resultssupporting

confidence: 63%

“…Such nematiclike patterns are actually rather unusual in Langmuir films, and the published reports always involve liquidcrystalline materials. 13,29,30 Similar structures have been obtained more frequently in surface-induced films, 31 freestanding films (although with artificial means in this case [32][33][34] ), hybrid films, 35 and also with LC materials. Tabe et al describe similar looking Schlieren textures in a Langmuir film obtained with a smectic C compound.…”

Section: Resultssupporting

confidence: 59%

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Layering Transitions and Schlieren Textures in Langmuir Films of Two Organic Radicals

Bourgogne

Nakatsuji

2004

Langmuir

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Two paramagnetic radicals have been investigated in terms of their film-forming properties at the air-water interface. Although the radicals failed to display any mesomorphic behavior in the bulk, they were found prone to built-up multilayer films on the Langmuir trough. The molecules seem to dimerize in the upper layers of the films that exhibit striking Schlieren textures when observed with Brewster angle microscopy. These Schlieren textures, together with the ability to form multilayers, indicate that the molecules came close to displaying smectic mesomorphism. A tentative model of the layers' structure is proposed, and a suggestion for synthesizing new molecules with actual mesomorphism is offered. The presented results show that the study of the behavior of molecules at the air-water interface can shed a new light on their behavior in the bulk and help in the design of new magnetic mesogens.

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Section: Resultssupporting

confidence: 63%

Section: Resultssupporting

confidence: 59%

Layering Transitions and Schlieren Textures in Langmuir Films of Two Organic Radicals

Bourgogne

Nakatsuji

2004

Langmuir

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“…Such nematic-like patterns are rather unusual in Langmuir films, ,− but they have been obtained more frequently in surface-induced films, free-standing films (though with artificial means in this case − ), and hybrid films . Tabe et al describe similar looking Schlieren textures in a Langmuir film obtained with a smectic C compound.…”

Section: Resultsmentioning

confidence: 95%

Organization of a Polar Molecule at the Air−Water Interface

et al. 2004

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We have studied the behavior of a low molecular mass organosiloxane ferroelectric liquid crystal at the air−water interface. Data obtained with Langmuir isotherms, surface potential measurements, and Brewster angle microscopy are presented and discussed. The compound forms films on the Langmuir trough, with phase transitions to multilayers upon compression. As seen with Brewster angle microscopy, the monolayers are optically isotropic whereas striking birefringent structures develop in the multilayer films. These periodic structures result from a surface elasticity phenomenon.

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Linear splay elasticity in surface-induced films of tilted smectic liquid crystals

Galerne

Najjar²

2004

Phys. Rev. E

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The prefrozen films that may be observed at the surface of isotropic liquid crystal droplets, close to the isotropic-smectic phase transition, or surface-induced films, are essentially asymmetric. If moreover, the molecules are tilted inside the smectic layers, as in the smectic-C (SmC) or smectic-C(A) (SmC(A)) phases, the c director that we may define as the order parameter of the film, is a real vector. Thus, the surface-induced films of MHTAC exhibit vectorial or polar properties, though the molecules are not chiral. The film free energy therefore contains a surface-elasticity term, K(1)c(2) c, that is a linear function of the splay distortion, and that may be negative enough to promote a mechanical instability. A spontaneous c distortion, or c modulation, then invades the whole film and produces an array of parallel stripes, with a typical four-fringe periodicity when observed between crossed polarisers. Here, we present optical measurements of the distortion for different film thicknesses, and we propose a linear analysis of the data to test our model. Due to the limitations inherent to the Fourier expansion that we use, the calculations are valid only between two limits: a large q limit where splay domains collapse into disclination lines, and a small q borderline below which the distortion evolves towards a system of independent solitons. We find that the sign of the spontaneous splay elastic constant K1 alternates as a function of the number of layers, N, a property that is reminiscent of the alternate structure of the SmC(A) phase. We argue that the two-dimension elastic constant, K1, originates from the interactions between the molecules in contact to the isotropic phase, and we deduce K1 approximately -(-1)(N)x10(-11) N and the elastic anisotropy, with a ratio of the splay over bend elastic constants K(s)/K(b) approximately 4.5. Similar properties could be observed also in other types of ultrathin films, e.g., in free-standing, ferroelectric (SmC*) or antiferroelectric (SmC(*)(A)), films, in Langmuir films, and even in particular biological films. In some cases, a second, electric instability may occur and superimpose onto the elastic one.

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Bend Elastic Constant in Ferroelectric Free Standing Films of Tilted Smectics

Cited by 5 publications

References 5 publications

Layering Transitions and Schlieren Textures in Langmuir Films of Two Organic Radicals

Layering Transitions and Schlieren Textures in Langmuir Films of Two Organic Radicals

Organization of a Polar Molecule at the Air−Water Interface

Linear splay elasticity in surface-induced films of tilted smectic liquid crystals

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