Solid state polymorphism of liquid crystals in confined geometries

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Solid polymorphism in 4-alkyl-4'-cyanobiphenyl (nCB) compounds is typically investigated concerning thermal history.
• Confined systems offer unique environments for studying phase behavior distinct from bulk materials.

Purpose of the Study:

• To investigate the formation and structure of metastable solid phases of 4-octyl-4'-cyanobiphenyl (8CB) within porous silica matrices.
• To characterize these confined solid phases using advanced spectroscopic and diffraction techniques.
• To correlate the structural features of metastable solid phases with those of mesophase structures.

Main Methods:

• Neutron diffraction: Utilized to probe the structural arrangement of atoms within the confined 8CB phases.
• Raman spectroscopy: Employed to analyze molecular vibrations and identify different solid-state structures.
• Confinement in porous silica matrices: A key experimental approach to induce and stabilize metastable phases.

Main Results:

• Identification of three distinct metastable solid states of 8CB within silica matrices.
• Characterization of one crystalline phase (K') and two frozen-in smectic-like phases (K(s) and K'(s)).
• Structural analysis provides insights into the influence of confinement on molecular ordering.

Conclusions:

• Porous silica matrices induce the formation of metastable solid phases in 8CB, beyond those observed under thermal history variations.
• The identified solid phases (K', K(s), K'(s)) exhibit unique structures influenced by the confining environment.
• Understanding these confined solid phases is crucial for their potential applications in advanced materials and devices.