Abstract
Collective excitations and field influence are investigated in tilted or orthogonal layered liquid crystal smectic (Sm) phases in a chiral hydrogen bonded (HB) calamitic dimer 10OBA:M*SA:10OBA by low-frequency dielectric spectroscopy. Phase transition temperatures, hysteresis, and phase thermal ranges are determined. The hysteresis in SmC* reveals the storage device suitability. The magnitude of the tilt angle in SmC* infers moderate viewing angle. The growth of primary order parameter tilt angle θ(T) infers long range interaction in SmC*. The growth of ferroelectric (FE) relevant secondary order parameter polarization Ps(T) infers strong layer-over-layer helical coupling of transverse dipole moment μt. Dispersion (loss vs permittivity) in 1D SmC*, 3D orthogonal SmBcryst, and 3D hexagonal tilted SmG crystal phases infers two distinct collective modes, viz., high frequency soft mode (SM) and low frequency Goldstone mode (GM). The dielectric strength of the SM in the SmC* phase confirms the FE Curie–Weiss behavior. The GM persists down to low temperature 3D LC phases. The AF order in SmC* is smeared by high temperature thermal fluctuations. A bias field resolves the GM in SmC* to reveal antiferroelectric (AF) modes. AF order manifested as GM1 and GM2 is explained by distinct Ps helices with different relaxation frequencies fR1 and fR2. GM1 and GM2 in 3D SmBcryst and SmG phases are explained by quenching by crystal field. HB LC dimer with a just shifted chiral center promoted the occurrence of field induced AF modes. AF P-switching in SmC* infers the gray scale mode. Trends of dielectric parameters, relaxation frequency, loss maximum, activation energy, dielectric strength, distribution parameter, etc., are discussed with respect to utility in appliances.
Highlights
Liquid crystal (LC) phase structures represent uniquely referred rare systems1,2 used to verify the melting transition theories in systems of 1, 2, or quasi-2-dimensional crystals and topological insulators
hydrogen bonded (HB) LC dimer with a just shifted chiral center promoted the occurrence of field induced AF modes
● Phase transitions can be detected by capacity and loss factor measurements
Summary
Liquid crystal (LC) phase structures represent uniquely referred rare systems used to verify the melting transition theories in systems of 1-, 2-, or quasi-2-dimensional crystals and topological insulators. The ferroelectric (FE) smectic-C∗ phase with chiral molecules in surface stabilized geometry (SSFLC) is reported to exhibit a faster micro-second response. Sub-micro (or nano)-second response is sparingly reported for electro-clinic (EC) effects in SmC∗ phases, its utility remained untapped in devices due to the paucity of data. If the sample thickness is less than the pitch of the polarization helix, the P-vector switches OFF and ON toward the substrate as per the direction of the ac field. If antiferroelectric (AF) response is realized in FE LCs, P-switching can be harnessed in gray scale mode devices. Field response investigations for collective excitations in ferroelectric liquid crystals (FLCs) are expected to reveal the mechanism and strength of the scitation.org/journal/adv cooperative domain response in terms of the molecular architecture. As calamitic LCs possess macromolecular dimensions (∼100 μm), collective response in FLCs is preferentially investigated, analyzed, and optimized by low-frequency (LF) dielectric relaxation studies
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