arXiv subjects

Jan P. F. Lagerwall

Publications and source records attributed to Jan P. F. Lagerwall.

4 recordsLinked to original sources

arXiv2026

Exotic topological defects and director fields in free-floating spherical ferroelectric nematic liquid crystal shells

Ferroelectric nematic (NF) liquid crystals exhibit polar symmetry and large polarization, giving rise to phenomena absent in conventional apolar nematics. We investigate NF liquid crystals confined to free-floating spherical shells with tangential boundary conditions, enforcing a total topological defect charge of +2. We conjecture that ferroelectric nematics avoid splayed configurations with half-integer defects, common in apolar nematic shells, instead concentrating the topological charge into escaped azimuthal +1 defects requiring only bend and twist. Indeed, at room temperature in the NF phase, our thin RM734+DIO shells with inner and outer aqueous poly(vinyl alcohol) solutions develop an azimuthal director field around two antipodal +1 bend-twist defects. The non-centrosymmetric nature and the azimuthal director configuration of the shells in the NF phase are confirmed also through second-harmonic generation microscopy. At intermediate temperature the antiferroelectric Nx phase generates a new exotic texture rife in zigzag lines in the shells. In the regular N phase at high temperature, the shells develop the usual four +1/2 disclinations located near the thinnest point. Our study highlights the rich platform offered by spherical shells to study the behavior of exotic liquid crystals subject to topological constraints, possibly opening new paths to apply the highly responsive ferroelectric nematic phase

cond-mat.soft↗

arXiv2022

Embedding Intelligence in Materials for Responsive Built Environment: A Topical Review on Liquid Crystal Elastomer Actuators and Sensors

Liquid Crystal Elastomers (LCEs) are an exciting category of material that has tremendous application potential across a variety of fields, owing to their unique properties that enable both sensing and actuation. To some, LCEs are simply another type of Shape Memory Polymer, while to others they are an interesting on-going scientific experiment. In this visionary article, we bring an interdisciplinary discussion around creative and impactful ways that LCEs can be applied in the Built Environment to support kinematic and kinetic buildings and situational awareness. We focus particularly on the autonomy made possible by using LCEs, potentially removing needs for motors, wiring and tubing, and even enabling fully independent operation in response to natural environment variations, requiring no power sources. To illustrate the potential, we propose a number of concrete application scenarios where LCEs could offer innovative solutions to problems of great societal importance, such as autonomous active ventilation, heliotropic solar panel systems which can also remove snow or sand autonomously, and invisible coatings with strain mapping functionality, alerting residents in case of dangerous (static or dynamic) loads on roofs or windows, as well as assisting building safety inspection teams after earthquakes.

cond-mat.soft↗

arXiv2020

Dynamic tuning of the director field in liquid crystal shells using block copolymers

When a nematic liquid crystal (LC) is confined on a self-closing spherical shell, topological constraints arise with intriguing consequences that depend critically on how the LC is aligned in the shell. We demonstrate reversible dynamic tuning of the alignment, and thereby the topology, of nematic LC shells stabilized by the nonionic amphiphilic block copolymer Pluronic F127. Deep in the nematic phase, the director is tangential to the interface, but upon approaching the temperature TNI of the nematic-isotropic transition, the director realigns to normal. We link this to a delicate interplay between an interfacial tension that is nearly independent of director orientation, and the configuration-dependent elastic deformation energy of an LC confined in a shell. The process is primarily triggered by the heating-induced reduction of the nematic order parameter, hence realignment temperatures differ by several tens of degrees between LCs with high and low TNI, respectively. The temperature of realignment is always lower on the positive-curved shell outside than at the negative-curved inside, yielding a complex topological reconfiguration on heating. Complementing experimental investigations with mathematical modeling and computer simulations, we identify and investigate three different trajectories, distinguished by their configurations of topological defects in the initial tangential-aligned shell. Our results uncover a new aspect of the complex response of LCs to curved confinement, demonstrating that the order of the LC itself can influence the alignment and thereby the topology of the system. They also reveal the potential of amphiphilic block copolymer stabilizers for enabling continuous tunability of LC shell configuration, opening doors for in-depth studies of topological dynamics as well as novel applications in, e.g., sensing and programmed soft actuators.

cond-mat.soft↗

arXiv2020

High-contrast imaging of 180° ferroelectric domains by optical microscopy using ferroelectric liquid crystals

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an electric field gives rise to an immediate and lasting optical response when an appropriately aligned FLC is observed between crossed polarizers, with one field direction yielding a dark image, and the opposite direction yielding a bright image. Here this peculiar electro-optic response is used to image, with high optical contrast, 180° ferroelectric domains in a crystalline substrate of magnesium-doped lithium niobate. The lithium niobate substrate contains a few domains with upwards electric polarization surrounded by regions with downward electric polarization. In contrast to a reference non-chiral liquid crystal that is unable to show ferroelectric behavior due to its high symmetry, the FLC, which is used as a thin film confined between the lithium niobate substrate and an inert aligning substrate, reveals ferroelectric domains as well as their boundaries, with strong black and white contrast. The results show that FLCs can be used for non-destructive read-out of domains in underlying ferroelectrics, with potential applications in e.g. photonic devices and non-volatile ferroelectric memories.

cond-mat.mtrl-sci↗