The formation of stable freely suspended filaments is an interesting peculiarity of some liquid crystal phases. So far, little is known about their structure and stability. Similarly to free-standing smectic films, an internal molecular structure of the mesophase stabilizes these macroscopically well-ordered objects with length to diameter ratios of 10(3) and above. In this paper, we report observations of smectic liquid crystal fibers formed by bent-shaped molecules in different mesophases. Our study, employing several experimental techniques, focuses on mechanical and structural aspects of fiber formation such as internal structure, stability, and mechanical and optical properties.
This paper describes an investigation of mechanical properties of freely suspended liquid filaments. These unique fluid microstructures may be formed by layered liquid crystalline mesophases. The filaments are electrically deflected and stimulated to mechanical oscillations. Resonance frequencies and damping rates are recorded. We present a model for a basic description of the dynamics, which is used to evaluate and to discuss the forces involved. The dependence of the oscillation parameters upon geometrical parameters and temperature is analyzed.
We report a novel type of electro-optical switching in a tilted smectic phase of bent-shaped mesogens. The switching consists of a continuous stage and two bistable transitions. Detailed optical and electro-optical measurements using high-speed imaging are given and possible interpretations of the experimental results are discussed.
Stable free-standing liquid filaments formed by some layered mesophases of bent-core mesogens are unique structures. Some of their physical properties have been analyzed in recent studies, but their microscopic structure and conditions for stability have still been unclear. We explore details of filament shapes and surface profiles of filaments drawn in liquid crystal phases of bent-core mesogens by AFM and SEM measurements, and we present a microscopic structure model. Conclusions on the stabilizing mechanisms are drawn. Qualitative differences in mechanical properties are found for different mesophases, even though the macroscopic appearance of the filaments is very similar.
Some liquid crystalline phases of bent-core mesogens are known to form stable freely-suspended filaments with length to diameter ratios of 1000 and larger. These structures can behave like thin liquid chords. We study filament oscillations excited with harmonic sound waves. From amplitudes of the filament motion and phase shifts respective to the harmonic excitation signal we develop a model for the filament dynamics. Like in solid chords, the resonance frequency f 0 is inversely proportional to their length. The dependence of f 0 upon the filament radius allows one to draw conclusions on the nature of the filament tension. For thin filaments, this tension can be largely attributed to surface tension, while for thick filaments there must be other, bulk contributions in addition. The decay time of the filament oscillations is proportional to the filament length. This can be explained by the assumption that dissipation is restricted to the two filament ends. An important observation is that thick filaments often deviate significantly from cylindrical shape.
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