Crystalline smectic-B films as fluctuating systems: static and dynamic x-ray scattering

Area of Science:

• Condensed matter physics
• Materials science
• Soft matter physics

Background:

• Smectic films exhibit thermal fluctuations influencing their properties.
• Crystalline-B and smectic-A phases have distinct positional order.
• Understanding fluctuations is key to material behavior.

Purpose of the Study:

• To characterize thermal fluctuations in free-standing crystalline-B smectic films.
• To compare fluctuation behavior with smectic-A films.
• To identify the underlying physical mechanisms.

Main Methods:

• Static and dynamic x-ray scattering techniques were employed.
• X-ray photon correlation spectroscopy (XPCS) was used to study dynamics.
• Analysis focused on thermal fluctuations and their impact on film properties.

Main Results:

• Crystalline-B films show fluctuation behavior similar to smectic-A films.
• The characteristic Landau-Peierls instability of smectic-A films is absent in crystalline-B films.
• Dynamic fluctuations were explicitly observed using XPCS.

Conclusions:

• The observed fluctuation behavior in crystalline-B films is attributed to a small shear elastic constant (C44).
• Despite 3D positional order, crystalline-B films exhibit similar fluctuation dynamics to smectic-A films.
• The findings provide insights into the mechanical and dynamic properties of smectic liquid crystals.