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P Cluzeau

Publications and source records attributed to P Cluzeau.

6 recordsLinked to original sources
PubMed2005

Interaction of surfaces in smectic membranes and their instability near thinning transitions.

We report measurements of the interaction between surfaces of the presmectic membrane above the temperature of transition to the phase without layer ordering. Investigations were performed employing cholesteric droplets embedded in the membrane in the temperature range of thinning transitions. Upon heating, the difference between the membrane tension and surface tension of the bulk sample decreases sufficiently, which leads to membrane instability. After the thinning transition, the membrane returns to a stable state with a larger value of surface interaction.

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PubMed2003

Self-organization of N(*) inclusions in SmC(*) free-standing films.

The behaviour of freely suspended smectic-C* ( SmC(*)) films at the bulk SmC(*)-cholesteric ( N(*)) phase transition has been investigated using polarized-reflected-light microscopy. Our experimental observations show that above the bulk SmC(*)- N(*) phase transition the N(*) order appears in different ways according to the film thickness. In thin films, the conventional layer-by-layer thinning occurs. In films of intermediate thickness N(*) inclusions nucleate inside the SmC(*) film. The distortions of the in-plane orientational order of the SmC(*) host phase induce elastic interactions between the inclusions and lead to their self-organization in chain-like structures. Both the dynamic of the chaining and the parameters driving the equilibrium distance between the inclusions in the chain are investigated. In thick films, N(*) fingers grow inside the film. The influence of the experimental conditions on the various processes is analysed.

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PubMed2002

Interlayer structures of the chiral smectic liquid crystal phases revealed by resonant X-ray scattering.

The structures of the liquid crystalline chiral subphases exhibited by several materials containing either a selenium or sulphur atom have been investigated using a resonant x-ray scattering technique. This technique provides a unique structural probe for the ferroelectric, ferrielectric, antiferroelectric, and SmC(*)(alpha) phases. An analysis of the scattering features allows the structural models of the different subphases to be distinguished, in addition to providing a measurement of the helical pitch. This paper reports resonant scattering features in the antiferroelectric hexatic phase, the three- and four-layer intermediate phases, the antiferroelectric and ferroelectric phases and the SmC(*)(alpha) phase. The helicoidal pitch has been measured from the scattering peaks in the four-layer intermediate phase as well as in the antiferroelectric and ferroelectric phases. In the SmC(*)(alpha) phase, an investigation into the helical structure has revealed a pitch ranging from 5 to 54 layers in different materials. Further, a strong resonant scattering signal has been observed in mixtures of a selenium containing material with as much as 90% nonresonant material.

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PubMed2001

Orientational ordering in the chiral smectic-C*FI2 liquid crystal phase determined by resonant polarized x-ray diffraction.

High-resolution resonant polarized x-ray diffraction experiments near the sulfur K edge have been performed on free-standing liquid crystal films exhibiting the chiral smectic-C*FI2 phase. It is widely accepted that this phase has a four-layer repeat unit, but the internal structure of the repeat unit remains controversial. We report different resolved features of the resonant x-ray diffraction peaks associated with the smectic-C*FI2 phase that unambiguously demonstrate that the four-layer repeat unit is locally biaxial about the layer normal and that the measured angle, describing the biaxiality, is in good agreement with optical measurements.

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PubMed2001

Interactions between colloidal inclusions in two-dimensional smectic-C* films.

We report an experimental study of colloidal inclusions in free-standing films of smectic-C* liquid crystal. The inclusions are cholesteric droplets that form above the bulk smectic-C*-7cholesteric transition temperature. Each droplet confined in a two-dimensional (2D) system, is accompanied by a topological defect. The distortions of the in-plane orientational order of the smectic-C* film induce elastic interactions between the droplets. As in 3D water nematic emulsions, a short-range repulsion and a long-range dipolar attraction govern the stability of the inclusions and lead to their organization in chainlike structures. Our results are in agreement with recent theoretical predictions.

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PubMed2000

Formation of string defects at thinning transitions in smectic-C* free-standing films

The layer thinning transitions in freely suspended smectic-C* films have been investigated. The defect structure formed by stringlike lines was observed just before the thinning transitions. The string defects disappear after the thinning transition and appear again near the temperature of the next thinning transition. These results clearly indicate that thin free-standing films at the thinning transitions are slightly below the melting temperature of the interior layers.

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