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Polarized light microscopy image of an optical cell containing the chiral mixture infiltrated with nitric acid from the right side. The concentration of acid molecules increases from left to right.
Source publication
In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal insid...
Contexts in source publication
Context 1
... expected, the optical properties of the cholesteric mixture were influenced by the presence of acid molecules. Figure 2 shows a polarized light optical microscopic image of the optical cell, the acid was infiltrated from the right. The red color on the left is the one shown by the cell prior to the nitric acid infiltration. ...
Context 2
... the liquid crystal mixture may lead to both a variation of the microdroplets interface conditions and to a change of free ions density. In this case, electrostatic effects could shield van der Waals forces, that align the liquid crystal molecules, varying the liquid crystal order parameter and hence the birefringence properties, as shown in Fig.2 and in Fig.4. Moreover, the acid molecules are responsible for the shift of the fluorescence: this effect, know as solvatochromism, is due mainly to the dielectric constant and hydrogen bonding of the solvent. In this case, the increasing of the acid concentration inside the emulsion implies a polarity growth, and this is reflected by the ...
Citations
... If the pitch of the helix is comparable with the wavelength of visible light, Bragg type reflection is observed from microspheres. This optical feature can be exploited in applications in photonics [1], sensing [2] and anti-counterfeiting [3]. ...
Induced or spontaneous chirality in natural systems is an intriguing issue. In recent years, a lot of attention has been focused on chirality of chromonic liquid crystals, a class of materials that is able to self-assemble in columnar structures. However, the mechanism involved in the arising of chirality in these materials, that starts at the molecular level and controls the supramolecular structure, is poorly understood; however, it is certainly affected by ionic strength. In this work we present the results obtained doping Cromolyn, a chromonic material, with a strong helical-twisting-power peptide, and confining it in a spherical geometry. We demonstrate, by means of optical polarized microscopy and structural analysis, that both the geometrical constraint and the presence of the chiral dopant enhance the chiral effect; we also demonstrate that they favor the rise of a highly ordered helical superstructure, that may be optimized upon adding an ionic dye to the system. Finally, we report a procedure for the preparation of free-standing polymeric films, embedding and preserving the microspheres, and paving the way for the creation of biocompatible and eco-friendly optical devices to be used in the sensor and anticounterfeiting fields.
Chromonic liquid crystals have recently received a lot of attention due to their spontaneous self-assembly in supramolecular columnar structures that, depending on their concentration in water, align to form a nematic liquid crystalline phase. The chirality may be induced in chromonics by adding chiral moieties to the nematic phase or enhanced by confining them in curved geometrical constraints. This review summarizes the recent research developments on chiral chromonic liquid crystals confined in spherical geometry, relating the results to what was observed for thermotropic liquid crystals in the same conditions. The review focuses on the studies carried out on commercially available nematic chromonics, investigating the effects on their topologies in different anchoring conditions and different chiral dopants and suggesting an application in the sensor field.
Chirality emergence in biological systems is common but the chiral expression from the molecular to macroscopic level in water‐based systems is poorly understood. Among water‐based systems, chromonic liquid crystals have recently received a lot of attention due to the spontaneous chirality they show when confined in curved geometries. Confinement of chiral‐induced chromonics is not trivial since they are three component systems whose time stability is a delicate thermodynamic balance. In this work, a well‐defined periodic Frank–Pryce texture, typical of chiral thermotropic liquid crystals, is observed in microspheres of a chiral induced chromonic embedded in a poly(dimethylsiloxane) matrix. This texture slowly degrades in time and a possible mechanism behind the degradation process is suggested via X‐ray diffraction and atomic force microscopy measurements on thin chromonic films. To stabilize this texture and to control the structure periodicity, cations are added to the three components system in an attempt to tune the non‐covalent interactions between molecules and supramolecular stacks. The study of the effects of this addition allows for better insight into the molecular interactions that occur in the chiral induced mesophase. This is a crucial point in view of possible biocompatible technological applications.
