# Chiral Chromonics Confined in Spherical Geometries
## 5 Induced Chiral Chromonics in Microspheres
### Chiral Induction in DSCG  
The chirality was successfully induced in DSCG using three different types of chiral amino acids, i.e., L-alanine, L-lysine and trans-Hyp (Figure 12) with different helical twisting powers [47]. The optical properties of the chiral chromonics were studied as a function of three different types of confining matrices. It is known that paraffin induces a planar alignment at the interface. When L-alanine 10 wt% was dissolved in DSCG 13 wt%, the water solution and microspheres were produced, and interesting textures were observed. Concentric periodic rings were visible at the borders of the microsphere and did not cover the entire area (Figure 13a). The measured periodicity was 8.6 \(\pm\) 0.5 \(\upmu\)m. The main problem with the use of paraffin is that the chiral textures or textures connected to chirality induction are not always observable in the microspheres. Additionally, there are problems related to the coalescence and quick water evaporation. The use of silicon oil (49.3 cSt, [PERSON], Merck KGaA, Darmstadt, Germany) did not help in preventing the coalescence and the concentric rings were less defined than in the previous case (Figure 13b). The periodicity of the rings was approx. 7.0 \(\pm\) 0.5 \(\upmu\)m. The best-defined optical configurations were obtained through the use of polydimethylsiloxane (PDMS). The microspheres exhibited a well-defined chiral texture with concentric circles. The Frank-Pryce texture, which propagates from the borders to the central core, was already observed for native chiral chromonics (Figure 13c). In addition, the presence of radial disclinations was clearly visible, resembling what was observed in the thermotropic liquid crystals. The possibility of obtaining this kind of texture in the chiral chromonic liquid crystal microspheres was not obvious, because it was a three-component system composed mainly of water, whose temporal stability was a delicate thermodynamical equilibrium. Nevertheless, the chiral texture was well-defined, and the pitch was homogeneous. For example, as shown in Figure 13c, the diameter of the microsphere was approx. 89 \(\upmu\)m with a pitch of 10.7 \(\pm\) 0.5 \(\upmu\)m. Additionally, the use of PDMS as matrix was extremely efficient in preventing the coalescence and water evaporation. Not all the chiral dopants were effective in inducing the chirality in DSCG. Figure 14a shows the typical texture observed in a microsphere containing DSCG 13 wt% and L-lysine 10 wt% in paraffin, while Figure 14b shows the texture of a microsphere containing DSCG 13 wt% with 26 wt% of trans-Hyp, whose value was very close to the solubility limit of this dopant. L-lysine was less effective than trans-Hyp for inducing the chirality, with the latter allowing researchers to obtain a perfect Frank-Pryce texture showing a well-defined Maltese cross when observed between crossed polarizers. The average measured half-pitch was 1.65 \(\pm\) 0.10 \(\upmu\)m.  
Figure 12: Molecular structure of (**a**) L-alanine, (**b**) L-lysine and (**c**) trans-4-hydroxy-L-proline. Figure 13: DSCG 13 wt% and L-alanine 10 wt% in (**a**) paraffin, (**b**) silicon oil and (**c**) PDMS. To understand the role of chiral amino acids and to investigate their position with respect to the supramolecular aggregates, X-ray diffraction measurements were carried out. The best performing amino acids--L-alanine and trans-Hyp--were used to prepare the chiral DSCG samples. The analysis was performed on chiral chromonic dried thin films deposited on thin solid films of PDMS. A slow drying procedure was carried out in controlled humidity and temperature conditions in order to allow the supramolecular aggregates to self-assemble in well-ordered phases. As visible in Figure 15, the DSCG nematic phase, drying slowly, turned into the hexagonal phase that was observed at a small angle. When L-alanine was added, it favored a pair molecule interaction (supramolecular diffraction peaks visible in the XRD pattern).