Fluctuations and clinicity in tilted smectic liquid crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Soft Matter Physics

Background:

• Tilted smectic liquid crystals predominantly display synclinic (Sm-C) ordering, characterized by a uniform tilt direction across layers.
• Anticlinic (Sm-C(A)) ordering, where tilt direction alternates between layers, is less common.

Purpose of the Study:

• To propose and provide evidence for a general entropic mechanism favoring synclinic ordering in tilted smectic liquid crystals.
• To investigate the role of molecular-scale fluctuations at smectic layer interfaces.

Main Methods:

• Computer simulations of the hard spherocylinder system (L/D=5).
• Analysis of entropy differences between synclinic and anticlinic states.
• Tracing entropy differences to molecular-scale interface fluctuations.

Main Results:

• The synclinic state exhibits higher entropy than the anticlinic state for large tilt angles in the simulated system.
• This entropy difference is directly attributable to molecular-scale fluctuations at the layer interface.
• Bent molecular conformations in anticlinic materials can suppress interface fluctuations, hindering synclinic preference.

Conclusions:

• Polar molecular-scale fluctuations at smectic layer interfaces provide a general entropic mechanism favoring synclinic ordering.
• This mechanism explains the prevalence of Sm-C over Sm-C(A) phases.
• The suppression of interface fluctuations by molecular shape can lead to anticlinic ordering.