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Natasa Vaupotic

Publications and source records attributed to Natasa Vaupotic.

6 recordsLinked to original sources
arXiv2025

Interplay of polar order and positional order in liquid crystals -- observation of re-entrant ferroelectric nematic phase

We show that development of polar order may spontaneously destroy the lamellar structure of a liquid crystal. This results in an unusual sequence of phases with the ferroelectric nematic phase appearing below a non-polar smectic phase. The effect is related to unfavourable dipole interactions within the smectic layers and can be explained by Landau theory in which the temperature dependent term is non-monotonic as it is renormalized by spontaneous electric polarization.

cond-mat.soft↗
arXiv2012

Liquid crystals: a new topic in physics for undergraduates

The paper presents a teaching module about liquid crystals. Since liquid crystals are linked to everyday student experiences and are also a topic of a current scientific research, they are an excellent candidate of a modern topic to be introduced into education. We show that liquid crystals can provide a file rouge through several fields of physics such as thermodynamics, optics and electromagnetism. We discuss what students should learn about liquid crystals and what physical concepts they should know before considering them. In the presentation of the teaching module that consists of a lecture and experimental work in a chemistry and physics lab, we focus on experiments on phase transitions, polarization of light, double refraction and colours. A pilot evaluation of the module was performed among pre-service primary school teachers who have no special preference for natural sciences. The evaluation shows that the module is very efficient in transferring knowledge. A prior study showed that the informally obtained pre-knowledge on liquid crystals of the first year students on several different study fields is negligible. Since the social science students are the ones that are the least interested in natural sciences it can be expected that students in any study programme will on average achieve at least as good conceptual understanding of phenomena related to liquid crystals as the group involved in the pilot study.

physics.ed-ph↗
arXiv2005

Polarization modulation instability in liquid crystals with spontaneous chiral symmetry breaking

We present a theoretical model which describes the polarization modulated and layer undulated structure of the B7 phase and gives the phase transition from the synclinic ferroelectric B2 phase to the B7 phase as observed experimentally. The system is driven into the modulated phase due to the coupling between the polarization splay and the tilt of the molecules with respect to the smectic layer normal. The modulation wavelength and the width of the wall between two domains of opposite chirality are estimated.

physics.comp-ph↗
arXiv2004

Effect of optical purity on phase sequence in antiferroelectric liquid crystals

We use the discrete phenomenological model to study theoretically the phase diagrams in antiferroelectric liquid crystals (AFLCs) as a function of optical purity and temperature. Recent experiments have shown that in some systems the number of phases is reduced if the optical purity is extremely high. In some materials the SmC$_{A}^{\star}$ phase is the only stable tilted smectic phase in the pure sample. In the scope of the presented model this high sensitivity of the phase sequence in the AFLCs to optical purity is attributed to the piezoelectric coupling which is reduced if optical purity is reduced. We limit our study to three topologically equal phases - SmC$^{*}$, SmC$_α^{*}$ and SmC$_{A}^{*}$ and show that the reduction of optical purity forces the system from the antiferroelectric to the ferroelectric phase with a possible SmC$_α^{\star}$ between them. The effect of the flexoelectric and quadrupolar coupling is considered as well. If the phase diagram includes only two phases, SmC$^{\star}$ and SmC$%_{A}^{\star}$, the flexoelectric coupling is very small. The materials which exhibit the SmC$_α^{\star}$ in a certain range of optical purity and temperature, can be expected to have a significant flexoelectric coupling that is comparable with the piezoelectric coupling. And finally, when temperature is lowered the phase sequence SmA $\to $ SmC$%_α^{\star}$ $\to $ SmC$^{\star}$ $\to $ SmC$%_{A}^{\star}$ is possible only in materials in which quadrupolar coupling is very strong.

cond-mat.soft↗
arXiv2004

Switching mechanism in polar columnar mesophases made of bent-core molecules

The behavior of polar columnar phases made of bent shaped molecules (B_1Rev and B_1RevTilted) was studied under applied electric field. There are two competing mechanisms of switching in polar B_1RevTilted columnar phase: the collective rotation around the long molecular axis and the collective rotation around the tilt cone. Respectively monostable and bistable optical switching is observed for antiferroelectric B_1RevTilted phase. The main factor discriminating the type of the switching is a width of the column cross-section.

cond-mat.soft↗