A discrete phenomenological model of antiferroelectric liquid crystals is used to study the structures and phase transitions in bulk samples thin films. An important ingredient our investigations minimization free energy with respect modulus order parameter. simple version energy, which contains only nearest-neighbor next-nearest-neighbor layer interactions gives a complete diagram all observed smectic-${\mathrm{C}}^{*}$ $(\mathrm{Sm}{C}^{*})$ variant phases. In free-standing films, surface...

Freestanding smectic films give a unique possibility to study two-dimensional coalescence. We report experimental investigations in freestanding and detailed analysis of coalescence islands, circular regions larger thickness than the surrounding film. The driving force island is dislocation tension on boundary between obtained results enable one perform complex Stokes regime compare it theoretical predictions. applicability scaling arguments for description peculiarities domain dynamics...

Using optical microscopy, phase shifting interferometry and atomic force we demonstrate the existence of undulated structures in meniscus ferroelectric smectic-C* films. The is characterized by a periodic undulation smectic-air interface, which manifests itself striped pattern. instability disappears untilted smectic-A phase. modulation amplitude wavelength both depend on thickness. We study temperature evolution structure propose simple model that accounts for observed undulations.

Density of photonic states ρ(ω), group v(g), and phase v(ph) velocity light, the dispersion relation between wave vector k, frequency ω(k) were determined in a cholesteric crystal. A highly sensitive method (measurement rotation plane polarization light) was used to determine ρ(ω) samples different quality. In high-quality drastic increase near boundaries stop band oscillations related Pendellösung beatings are observed. low-quality properties strongly modified. The maximal value is...

Striped patterns in the meniscus of smectic membranes: free surface is distorted and forms wrinkles, bumps dimples.

In this article we review interactions and collective behavior of inclusions in free-standing smectic films with in-plane orientational ordering. The interact on large distances can form various self-organised structures. Topological defects the director field play a key role self-organization. Various types interaction are realized, including dipolar, quadrupolar mixed type. We describe different approaches which be used to modify inclusions. Effects polarity chirality host medium, external...

We report experiments on a ferroelectric membrane and droplets with tunable surface properties. In smectic membranes the configuration of c -director field near inclusions may be rearranged drastically temperature. The transformation results from competition between elastic polar properties membranes. demonstrate that anchoring conditions inclusion boundary are not fixed but depend A dipolar can evolve to mixed quadrupolar one. These modifications lead change interaction inclusions, their...

Transmission spectra and rotation of the plane polarization light were measured on perfect samples cholesteric liquid crystal. We found peculiarities spectral dependence related to Pendell\"osung oscillations that predicted theoretically but never observed experimentally. The experimental data are well described by expressions based an analytical solution Maxwell equations. An approach fundamental Kramers-Kronig relations is used describe optical properties photonic It shown rotatory power...

Photooptical properties of a new cholesteric mixture containing azobenzene-based chiral dopant were investigated. Presence photosensitive in the investigated liquid crystal enabled to effectively manipulate optical characteristics photonic band upon temperature change and illumination. Temperature dependence anisotropy orientational order parameter determined. The obtained results are compared with existing theories. Discrete multistable spectral position on illumination is realized.

We found that the nematic droplets in smectic membranes and configuration of c-director field near may rearrange drastically with droplet size temperature. Investigations were made quadrupolar droplets. Large are nearly circular, whereas small become elongated. The elongation increases decreasing size. At high temperature to be spindlelike two cusps on their boundary. observed transformations explained by competition between elastic energy director surface tension interface membrane.

We observed the formation of small satellite droplets from bridge at droplet coalescence. Investigations were made using a Hele-Shaw cell in two-phase region nematic-isotropic phase transition. In previous works on coalescence it was considered that before start there exists between outer fluid connecting regions two sides (outer bridge). After coalescence, appears (droplet bridge) and is broken. have shown are processes where after both can exist. This cardinally changes process. During...

The behavior of isolated inclusions (nematic droplets, smectic islands) and formation chains clusters from in oriented membranes have been studied. Investigations were performed which the molecular ordering was by an external magnetic field. At planar boundary conditions on interface between membrane different configurations c-director field observed: Coulombic, dipolar, quadrupolar, mixed. observed orientation their interactions self-organization correlate with predictions theory based...

Our experiments reveal that breaking of chiral symmetry in smectic membranes leads to a dramatic modification the collective behavior inclusions. We investigated nematic and cholesteric droplets, respectively, nonpolar formed by racemic mixture ferroelectric ones isomer. Inclusions polar induce substantially different elastic deformation c-director field: quadrupolar dipolar symmetry, respectively. Interaction between inclusions related with field self-organization into linear chains...

Recently Wang et al. [Phys. Rev. Lett. 104, 027801 (2010)] discovered a novel smectic-${C}^{\ensuremath{\ast}}$ liquid-crystal commensurate structure with six-layer period. Challenged by this discovery, we show that the observed and unusual sequence of polar phases can be explained in framework discrete Landau model phase transitions two-component order parameter. Peculiarities influence short-range long-range interactions on formation different sequences are discussed.

We revisit a theoretical approach based on the discrete Landau model of polar smectic liquid crystals. Treating equilibrium structures many length scales, we have analyzed different periodically modulated phases. Besides already known structures, obtained number other phases which are stable in narrow range (that is why can be termed as microphases) parameters and thermodynamic conditions. The sequence microphases represents so-called ``harmless staircase'' with oscillating periods....

In this paper we review various amazing features of polar smectic structures and phase transitions between them. a series experimental theoretical studies over the last decades, lot new unexpected have been observed described theoretically in realm liquid crystals. Not all these were correctly identified experimentally and/or interpreted theoretically. At least part, problem is uncertainty about which model can provide an adequate minimal description available data. The approach are...

We investigate in free-standing smectic films coalescence of holes (circular regions with thickness smaller than the surrounding film). This process can be considered as a two-dimensional analog bubbles three-dimensional fluid. A high speed video camera was used to study evolution domains at different stages coalescence. Special attention given investigations dependence size bridge between two initial stage coalescence, which numerous theoretical works and bears information on mechanism. It...

Droplets in smectic free-standing films interact due to elastic distortion of the c-director field and formation topological defects. Our experiments show that chirality liquid-crystal medium plays a key role interaction between droplets. We find configuration near droplets position defects on droplet boundary depend size film polarity. An intermediate dipolar quadrupolar is formed competition elasticity chirality. observed distance self-organized structures depends significantly changes...

Recently Wang et al. [Phys. Rev. Lett. 104, 027801 (2010)] reported the discovery of a novel multilayer phase in polar liquid crystals. The was unambiguously assigned to six-layer antiferroelectric structure (Sm-${C}_{d6}^{*}$) by resonant x-ray diffraction. This lead essential progress understanding nature phases. However, more recently, Chandani [Liq. Cryst. 38, 663 (2011)] same material clearly identified as ferrielectric five-layer (Sm-${C}_{d5}^{*}$) electric-field-induced...

We report measurements of the interaction between surfaces presmectic membrane above temperature transition to phase without layer ordering. Investigations were performed employing cholesteric droplets embedded in range thinning transitions. Upon heating, difference tension and surface bulk sample decreases sufficiently, which leads instability. After transition, returns a stable state with larger value interaction.

We study the topology of c-director field near topological defects with point core and a droplet in defect nonpolar smectic-C ferroelectric smectic-C* freestanding films using polarized optical microscopy. Free confined geometry droplets strong outer boundary condition are compared. The can be remarkably different around same charge S=+1. In films, splay deformation transforms into bend after nucleation. Heating film an S=+1 leads to dramatic change from splay. we found spiral structures...