Barbara Rovšek

Possible stable structures of chiral polar smectics with significant interactions between next nearest layers

Abstract We analyse stable structures in the model where interactions between the nearest and the next nearest layers are taken into acount. Interactions can be noncompeting or competing. We find five different stable structures stable at different values of model parameters. Three of them are already known: the ferroelectric SmC*, the antiferroelectric SmCA* phase and by recent experiments confirmed helicoidal short-pitch SmCα* structure. Aditionally we find two structures, the structure with a primitive cell which extends over 2 smectic layers SmC2* and SmC4* the primitive cell cosists of 4 smectic layers.

Anticlinic Surfaces in Freely Suspended Smectic Films Stabilized by Electrostatic Interactions

Abstract Electrostatic dipolar interactions between transversal polarizations of the finite and parallel surface smectic layers are shown to stabilize the anticlinic smectic-C surfaces in freely suspended smectic films formed from (anti)ferroelectric liquid crystals.

Making a cat's eye in a classroom

Three plain mirrors, perpendicular to each other, reflect a beam of light back into the direction it came from. An activity is suggested where pupils can employ this feature of perpendicular mirrors and make their own corner cube retroreflector—a kind of cats eye.

Surface transitions in free standing films of antiferroelectric liquid crystals within the discrete phenomenological model

Abstract Within the discrete phenomenological model of antiferroelectric liquid crystals we study phase transitions in free standing films. Commonly observed rise as well as recently reported lowering of the temperature of the transition from the SmA to the tilted phase, compared to the bulk transition temperature, can be explained in view of the excess surface order in the first case or missing inter-layer interactions at the surfaces in the second case. We also expose the possibility of forming non-planar SmCα phase in a narrow temperature region near the bulk SmA ⟷ SmC transition temperature, although the particular compound exhibits only SmA and SmC (or SmC*, if chiral) phases in the bulk sample.

SmCα phase in free standing films

Abstract Within the discrete phenomenological model of antiferroelectric liquid crystals we calculate the structure of the SmCαphase in free standing film consisting of N smectic layers. A temperature evolution of the structure is determined for an example of the bulk SmA ⇄ SmCα ⇄ SmC phase sequence.

Flexoelectrically induced polarization in polar smectic films

Abstract Phenomenological model of racemic ferroelectric and antiferroelectric liquid crystals, which considers both the tilt and the polarization order parameters explicitly, is presented. Free-standing films with few layers are analyzed within the model. Due to the flexoelectric coupling between the tilt and the polarization, a polarization appears in the tilt plane. Results of the theoretical analysis are compared with experimental observations.

The SmA ⟷ SmC* (SmC) phase transition in a planar cell with a polar surface coupling

Abstract The phase transition from the SmA to the lower-temperature SmC* or SmC phase in a restricted geometry of a planar cell is studied theoretically, considering a polar coupling of the ferroelectric liquid crystal to the surfaces. The λ-line in a (2L, T) phase diagram, where T is the temperature and 2L is the cell thickness, is determined numerically. The critical temperature Tc of the SmA ⟷ SmC* (SmC) phase transition exibits nonmonotonic dependence on the cell thickness 2L. Two tricritical points are found on the λ-line, which could be candidates for the Lifshitz points.

Short Pitch Smectic Structures in Electric Field

ABSTRACT When an external electric field is applied to short pitch polar smectics, their helical structures distort and unwind. The final transition to completely unwound structure can be continuous or discontinuous. Within the discrete phenomenological model the nature of the transition depends on the existence of the next-nearest neighboring layers interactions. If they are present, the transition is discontinuous. We try to elucidate this phenomenon.

Short Pitch Structures in Smectics with Interactions over More Than Two Layers

Abstract Phenomenological model of chiral polar smectics is introduced with interactions up to the fourth neighboring layers. The minimization of the free energy gives three stable structures: the ferroelectric Sm C* phase, the antiferroelectric Sm C A * phase and the hellicoidally modulated structure of the Sm C H * phase. The Sm C H * phase can be recognized as the Sm Cα* phase below Sm A phase and as the Sm C FI1* phase or as the Sm C FI1 phase when appearing between the Sm C* phase and the Sm CA* phase. Stability of these phases is analyzed and the phase diagram in the space of model parameters is presented.

Structures, transition temperatures, and macroscopic polarization of antiferroelectric liquid crystals in free-standing films

Within the framework of the phenomenological model that takes into account the interactions between the smectic layers explicitly, we analyze the structure, the transition temperatures and the macroscopic polarization of the free standing film formed by an antiferroelectric liquid crystal. Outer layers of the film interact only with the interior of the film and are therefore less tilted. Consequently, the transition temperatures from the tilted phase to the untilted smectic. A phase are lower than for bulk samples. Due to the chiral interactions the film possesses the macroscopic polarization which is for even lower than for bulk samples. Due to the chiral interactions the film possesses the macroscopic polarization which is for even number of layers parallel to the plane of the tilt, while for odd number of layers it is nearly perpendicular to the plane of the tilt.