What promotes smectic order: Applying mean-field theory to the ends

Area of Science:

• Materials Science
• Soft Matter Physics
• Chemical Physics

Background:

• Nematic liquid crystals can transition to smectic phases, but this behavior is particle-dependent.
• The shape of constituent particles, specifically their tips, plays a crucial role in determining whether a smectic phase forms.
• Molecular structure, such as the length of alkyl chains in N-CB molecules, also influences smectic phase formation.

Purpose of the Study:

• To investigate the critical role of particle tip geometry in the nematic-to-smectic phase transition.
• To understand how molecular structure, particularly tail length, affects liquid crystal phase behavior.
• To elucidate the mechanisms by which particle shape and tail length influence the stability of nematic and smectic phases.

Main Methods:

• Utilized a simplified two-dimensional model to simulate particle behavior.
• Modeled spherocylinders with rounded tips as "boubas" and ellipsoids with pointed tips as "kikis".
• Represented N-CB molecules as a core body with an attached polymer tail.

Main Results:

• Rounded tips (spherocylinders) promote smectic phase formation, unlike pointed tips (ellipsoids).
• Longer polymer tails (N≥8 carbons in N-CB molecules) are essential for smectic phase formation.
• Both rounded tips and longer tails reduce the accessibility of inter-layer space, destabilizing the nematic phase at lower densities.

Conclusions:

• Particle tip geometry is a key determinant of nematic-to-smectic transitions in liquid crystals.
• Molecular design, incorporating rounded tips and extended tails, can be used to control liquid crystal phase behavior.
• The findings provide insights into the fundamental principles governing phase transitions in soft matter systems.