This paper reviews nearly $20\phantom{\rule{0.3em}{0ex}}\text{years}$ of research related to antiferroelectric liquid crystals and gives a short overview possible applications. ``Antiferroelectric crystals'' is the common name for smectic formed chiral elongated molecules that exhibit number (Sm) tilted structures with variation strong-tilt azimuthal direction from layer (i.e., nonsynclinic structures). The phases have varying crystallographic unit periodicity few...

We studied the dielectric properties of a polar nematic phase (NF) sandwiched between two gold or ITO electrodes, serving as cell surface. In bulk, NF is expected to exhibit Goldstone mode (phason), because polarisation can uniformly rotate with no energy cost. However, coupling direction director and finite, confinement, even in absence aligning surface layer, induces some cost for reorientation polarisation, relaxation frequency phason measured kHz regime. The easily quenched by bias...

Abstract In a discrete phenomenological description of tilted smectic phases, the order parameter, which describes magnitude and direction tilt molecules, is defined for each layer. The free energy expansion in terms parameter takes into account interactions between nearest next layers, allows competing interactions. By minimizing system structure frustrated Sm C*α phase obtained.

Using a high resolution optical polarimeter, we have measured the temperature dependence of birefringence and rotation in chiral smectic liquid crystals that exhibit antiferroelectric, ferroelectric, intermediate phases. The magnitude tilt angle was determined from 4-(1-methyl-heptyloxycarbonyl-phenyl) ${4}^{\ensuremath{'}}$-octylbiphenyl-4-carboxylate (MHPOBC) 4-(1-methylheptyloxycarbonyl-phenyl) ${4}^{\ensuremath{'}}$-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). Both substances...

The free energy of antiferroelectric smectic liquid crystals which takes into account polar order explicitly is presented. Steric, van der Waals, piezoelectric, and flexoelectric interactions to the nearest layers, dipolar electrostatic next-nearest induce indirect tilt with chiral achiral properties, extend third- fourth-nearest layers. Although strength microscopic changes monotonically decreasing temperature, effective interlayer change nonmonotonically give rise a nonmonotonic modulation...

Abstract We present the analysis of static properties a simple phenomenological model antiferroelectric liquid crystals, capable explaining some different sequences phase transitions found experimentally. Stability shows existence three simply modulated phases. Results are summed up in diagrams with dependence on parameters model. The doubly incommensurate phases is predicted parts diagrams.

A critical end point above which an isotropic phase continuously evolves into a polar (ferroelectric) nematic with increasing electric field is found in ferroelectric liquid crystalline material. The approximately 30 K the zero-field transition temperature from to and at of order 10 V/μm. Such systems are interesting application view because strong birefringence can be induced broad range optically phase.

We present the experimental and theoretical evidence that a new Sm X phase made of asymmetric bent-shaped molecules has layered, nontilted, optically uniaxial polarly ordered structure with random direction layer polarization. The randomness results from sign degeneracy difference in polarization directions neighboring layers, although magnitude is constant. Lifting by external fields two additional structures are possible.

The phase diagram of the prototype antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl-4'-octyloxybiphengl-4-carboxylate (MHPOBC) in dependence enantiomeric excess was measured. It shown that Sm-C*beta very pure samples is Sm-C*(FI2) with a four-layer structure, and only after small racemization it transforms into ferroelectric Sm-C* phase. theoretically explained by taking account longer range bilinear short biquadratic interlayer interactions, lead to distorted clock...

The behaviour of polar, broken-layer-type columnar phases made bent molecules (B(1Rev) and B(1RevTilted)) was studied under an applied electric field. There are two competing mechanisms ferroelectric switching in the polar B(1RevTilted) phase: collective rotation around long molecular axis tilt cone. proposed model shows that main factor discriminating type is width column cross-section.

We present a continuum theoretical model describing the impact of chirality on nematic systems with large flexoelectricity. As opposed to achiral materials, where only one type modulated structure can exist in given material, predicts that stabilize several phases, which have already been observed experimentally [A. Zep et al., J. Mater. Chem. C 1, 46 (2013)].

Within the new phenomenological model of antiferroelectric liquid crystals, structures two phases, Sm CFI2* and CFI1* that appear in temperature range between C* CA* phase, are found. The structure phases is consistent with extensive optical, electro-optic, dielectric measurements performed on crystal R-10OTBBB1M7, for which resonant x-ray scattering studies have previously proven these three-layer (Sm CFI1*) four-layer CFI2*) periodic structure, respectively. biaxiality phase directly...

Ferroelectric behavior in the recently reported orthogonal ferroelectric Sm-A(d)P(F) phase an unsymmetric bent-core molecule with a carbosilane terminal group was studied. The ferroelectricity of unambiguously confirmed by optical second-harmonic generation activity absence electric field, response, and high dielectric strength. long-range polar order is consequence weakened interlayer coupling due to formation sublayers, which allows for parallel dipole moments molecules neighboring layers....

We show that the flexoelectric model of chiral and achiral modulated nematics predicts compression modulus is by orders magnitude lower than measured values. The discrepancy much larger in nematic phase, which value same order as nematics, even though heliconical pitch an larger. relaxation a one-constant approximation biaxial elastic used for does not solve problem. Therefore, we propose structural consistent with current experimental evidence can also explain large modulus: structure...

Structurally similar bent-core compounds were studied by the X-ray diffraction method. Modulated bilayer structures observed in lamellar and columnar B1Rev-type phases. Their formation is explained a general tilt SmCG structure. In case of phases modulations found to be incommensurate with block structure phase.

The ferroelectric (Sm C*)-antiferroelectric C*A)-reentrant (re Sm C*) phase temperature sequence was observed for systems with competing synclinic-anticlinic interactions. basic properties of this system are as follows: (i) the C* is metastable in range C*A; (ii) helix handedness inverts at both C*-Sm C*A and C*A-re-Sm transitions; (iii) threshold electric field that necessary to induce synclinic ordering decreases near C*A-Sm boundaries. All these properly described by a simple Landau model...

Abstract A phenomenological model of helicoidal antiferroelectric liquid crystals is analysed and the relaxational eigenfrequencies ferroelectric modes are evaluated in smectic phase, C* phase phase. In intermediate ferrielectric eigenmodes mixtures fluctuations.

It is generally accepted that the doping of chiral materials with achiral molecules diminishes chirality system. Here we report opposite phenomenon. was found structural smectic phases made rodlike molecules, Sm-C(*) or Sm-C(*)(A) phases, measured as reverse length helical pitch, enhanced by adding small amount bent-shaped molecules. The effect due to transfer between host and guest systems. Achiral become structurally interactions induces tilt polar order This induced then transferred back host.

Critical freezing of molecular rotation in an achiral smectic phase, which leads to polar ordering through the second order paraelectric-antiferroelectric (Sm-A-->Sm-APA) phase transition is studied theoretically and experimentally. Strong softening mode Sm-A highly intensive dielectric Sm-APA are observed due weak antiferroelectric interactions system. In response behaves critically upon biasing by a dc electric field. Such behavior found general for with significant quadrupolar interlayer coupling.

Material with the phase sequence $\mathrm{Sm}A\text{\ensuremath{-}}\mathrm{Sm}AP\text{\ensuremath{-}}\mathrm{Sm}CP$ is studied as an example of a system in which spontaneous electric polarization and molecular tilt develop independently at $\mathrm{Sm}A\text{\ensuremath{-}}\mathrm{Sm}AP$ $\mathrm{Sm}AP\text{\ensuremath{-}}\mathrm{Sm}CP$ transition, respectively. The temperature dependence clearly shows strong coupling between tilt. exhibits also very precritical fluctuations. Experimental...

A reentrant orthogonal smectic-$A$ (Sm$A$) phase below the tilted smectic-$C$ is established in a chiral liquid crystalline compound. The temperature evolution of layer spacing confirms monolayer structure both Sm$A$ phases, upper as well phase. reentrancy explained on basis mean field free energy taking into account nonmonotoneous dependence lowest term coefficient.

The paper presents a teaching module about liquid crystals. Since crystals are linked to everyday student experiences and also topic of current scientific research, they an excellent candidate modern be introduced into education. We show that can provide file rouge through several fields physics such as thermodynamics, optics electromagnetism. discuss what students should learn physical concepts know before considering them. In the presentation consists lecture experimental work in chemistry...

Non-symmetrical dimers have been synthesised, in which bent- and rod-shaped mesogenic molecules are linked by a flexible polymethylene spacer –(CH2) n –. It has shown that compounds = 5, 6 or 7 exhibit one (nematic), two (nematic smectic), no phases, respectively. These variety of anchoring transition behaviours depending on the (n 5 6) surfaces (polyimide for homeotropic planar alignment, perfluoropolymer surface). Discontinuous continuous planar-to-homeotropic orientational changes take...