Defect model of the smectic A-nematic phase transition

Helfrich, W.

doi:10.1051/jphys:0197800390110119900

Cited by 86 publications

(54 citation statements)

References 14 publications

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“…The foregoing observations of the modifications and disappearance of FCDs imply that the dislocations play a dominant role near the transition, due to their high mobility and their multiplication; such results appear as a characteristic feature of samples showing a SmA-N transition, (they are not documented, as indicated above for 10CB, when the SmA transforms to an isotropic phase), and seem to point towards a defect model of the transition, as suggested by several authors [10,11]. We will give more details on the mechanisms of the FCD modifications in a forthcoming publication [12]; these mechanisms are also visible in the case of homeotropic samples.…”

Section: Conclusion Other Elements Of Discussionmentioning

confidence: 75%

How Do Defects Transform at the Smectic A-Nematic Phase Transition?

Meyer

Kléman

2005

Molecular Crystals and Liquid Crystals

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Section: Conclusion Other Elements Of Discussionmentioning

confidence: 75%

How Do Defects Transform at the Smectic A-Nematic Phase Transition?

Meyer

Kléman

2005

Molecular Crystals and Liquid Crystals

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“…The weak diffuse scattering observed in the lamellar phase close to the transition is satisfactorily described as arising from the form factor of defects with a twin helical structure and interpreted as Burgers vector 2 screw dislocations. Although there is no measurement either of the screw dislocation length, its handedness or the defect density, it is likely that the lamellar-to-nematic (or lamellar-to-cholesteric with L-DMPC ) transition is induced by the defect spontaneous proliferation [31][32][33]. This picture differs markedly from the mechanism involving pores or ribbon-like defects as described by other groups close to nematic- [17,18,34], hexagonal- [35] or ordered bicontinuous- [36,37] to-lamellar transitions (refer to [38] for a review).…”

Section: Resultsmentioning

confidence: 99%

Lamellar-to-nematic phase transition in a lipid-surfactant mixture

Dhez

König

Roux

et al. 2000

The European Physical Journal E

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A lyotropic system, consisting of a lecithin (DMPC) and a non-ionic surfactant (C12E5) in water was studied. The system exhibits a lamellar-to-nematic phase transition. The nematic phase appears as the temperature is decreased and only exists in a very limited temperature and concentration range, for specific lipid-to-surfactant ratios. While a lamellar phase is found at higher temperatures in both mixed and pure C 12E5 systems, the transition to the nematic phase at lower temperatures coincides with a micellar phase in the pure C12E5 system. The transition appears to be driven by the strong temperature dependence of the surfactant film spontaneous curvature. The structural properties of the lamellar phase close to the lamellarto-nematic boundary have been studied by polarised light microscopy and small-angle neutron and X-ray scattering experiments. The signature of a helical defect with Burgers vector of magnitude 2 is apparent in our data, close to the lamellar-to-nematic phase transition. The proliferation of screw dislocations in the lamellar phase might be a plausible mechanism for driving this transition.

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“…2 of Ref. [2]) varies as R 4 was already well known in the literature [3]. The subsequent calculation using this expression for the polarizability has nothing whatsoever to do with the sign error in the text; Jackson is completely wrong in claiming that this invalidates the theory.…”

Section: Introductionmentioning

confidence: 84%