All Structures Great and Small: Nanoscale Modulations in Nematic Liquid Crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• The nanoscale structural organization in modulated nematic phases is a key area in liquid crystal research.
• Current understanding is incomplete, with macroscopic continuum elasticity models mistakenly applied to explain nanoscale phenomena.
• Previous work misidentified the low-temperature nematic phase (N) in CB-n-CB dimers as a twist-bend nematic.

Purpose of the Study:

• To elucidate the molecular organization and physical origins of nanoscale modulations in the N phase.
• To differentiate the N phase from theoretically predicted elastically modulated nematic phases.
• To propose a new classification for the observed nanoscale-modulated nematic phases.

Main Methods:

• Utilizing molecular theory and computer simulations.
• Applying Frank-Oseen elasticity theory for a theoretical formulation of one-dimensionally modulated nematics.
• Comparing experimental observations with theoretical models.

Main Results:

• The N phase is unrelated to the elastic deformations (bend, splay, twist) of continuum elasticity theory.
• The N phase exhibits spontaneous chirality and local polarity.
• Nanoscale modulations in the N phase originate from packing constraints of nonlinear molecules.

Conclusions:

• The N phase represents a new type of nematic phase, distinct from elastically modulated nematics.
• Its structure is dictated by molecular packing, leading to a chiral, locally polar organization.
• Further research into nonlinear molecular architectures is crucial for understanding novel liquid crystal phases.