ABSTRACT
We show how the inclusions of the nanoparticles or the clusters of nanoparticles in the liquid-crystalline smectic-A phase lead to layer deformations and may create a tilt in their vicinity, thus inducing locally a smectic-A-smectic-C transition. We have studied a freestanding film of "de Vries" compound, which exhibits the smectic-A-smectic-C transition without layer shrinkage, mixed with functionalized gold nanoparticles. The tilt induced by nanoparticle clusters, which decorate the edge dislocations, has been observed in the smectic-A phase. The tilt of liquid-crystal molecules near nanoparticles is a consequence of interaction of liquid-crystalline molecules with the surface of nanoparticles. The observed tilt may prove the concept of existence of a disordered tilt in the smectic-A phase of de Vries compounds. The tilt distribution near nanoparticles is discussed using both the smectic-A elasticity and local smectic-A-smectic-C transition.
Subject(s)
Gold/chemistry , Liquid Crystals/chemistry , Metal Nanoparticles/chemistry , Metal Nanoparticles/ultrastructure , Models, Chemical , Models, Molecular , Computer Simulation , Materials Testing , Molecular Conformation , Particle Size , Phase TransitionABSTRACT
A theory of the phase transition from the smectic-C* to the hexatic phase based on the free energy with the two different Lifshitz terms is presented. Competition between the elastic energies of the tilt angle and of the hexatic order leads either to the single helicoidal structure, or to the double modulated solitonlike structure, and the transformation between both can occur. The bond order and the tilt angle suppress each other and at the transition to the low-temperature hexatic phase a decrease of the tilt angle and an anomaly in the helical pitch occur. Approaching the hexatic phase transition the dielectric response is contributed mainly by the bond-order phason or (and) the tilt angle phason. While the bond-order phason frequency decreases the tilt angle frequency increases in the hexatic phase. Both situations are treated being observed in experiment.
ABSTRACT
Binary mixtures of two successive homologues from a series of 4-(4(')-alkoxy-biphenyl-4-yloxymethyl)benzoic acid 2-octanol esters exhibit a polar phase that differs from both ferroelectric (FE) and antiferroelectric (AF) phases, which exist in the pure compounds. When the concentration of the FE component is increased, this phase gradually changes its polar character from AF-like to FE-like, which is confirmed by the study of dielectric properties. Sample boundaries as well as the dc electric field introduce the FE phase, which remains stable after the field is switched off. Dielectric study confirms that this phase is composed of FE and AF clusters. The clusters arise due to frustration of FE and AF molecular order, which occurs as a result of the lowering of interlayer interactions.
ABSTRACT
We report an ellipsometric study of freely suspended films of a chiral liquid-crystal compound possessing the phase sequence smectic-C-smectic-A-isotropic with a very broad (67 K) smectic-A phase range. We observe a smectic-C-smectic-A surface transition which is situated more than 60 K above the bulk smectic-C-smectic-A transition temperature. Possible reasons for this unusually large temperature shift are discussed.
ABSTRACT
The smectic layer spacing of a nonfluorinated ferroelectric liquid crystal (FLC) compound with almost no shrinkage and only minor tendency to form zigzag defects was characterized by small angle x-ray diffraction. The material lacks a nematic phase. The smectic-A*-smectic-C* phase transition was studied by measuring the thermal and electric field response of the optical tilt and the electric polarization. These properties are described very well by a Landau expansion even without introduction of a higher-order Theta(6) term. This result suggests a pure second-order phase transition far from tricriticality and differs considerably from the typical behavior of the A*-C* transition in most FLC materials.
