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Optimizing strategies used for improving the stability and properties of blue phase (BP) liquid crystals directly impact device performance. Various factors ranging from molecular structure to sample size and substrate conditions can influence selective reflection and electro-optics of BPs. More recently, the technique of incorporating colloidal nanoparticle (NP) assemblies has been used to enhance BP ranges. In cubic BPs, disclination networks can act as trapping centers for NPs, reducing the high elastic energy cost of these regions, favoring BP stability. Organization of NPs in the defect regions can sustain stable 3D colloidal structures, widening the scope and applicability of BPs as photonic materials. Physical and chemical properties, size, and shape of the NPs can also determine the utilization of BPs for advanced applications like lasers and high quality displays. In view of this, a mixture of two calamitic chiral compounds in which all three BPs, viz., BPI, BPII, and BPIII, were induced was combined with rod-shaped CdSe/CdS quantum rods (QRs) and spherical CdSe quantum dots (QDs), which were specifically chosen due to their exceptional optical properties. This also provided an opportunity to investigate the effect of the shape of the NPs on the preferential stabilization of the BPs and on the electro-optic Kerr effect. QRs were found to be more efficient in enhancing the overall BP range, with an almost twofold increase of ∼27 °C with ∼0.5 wt. %. On the other hand, with QDs, the BP range showed an initial increase of 20 °C for ∼0.3 wt. %, which, however, decreased with a further increase in QDs. Another major difference is that the Kerr effect was active only in the BPIII in the case of QDs but is measurable in both cubic BPI and BPII in the case of QRs. The results have been described in terms of the organization of the nanocrystals within the defect lines and the lattice orientations imposed by the substrates. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) substrates are chemically modified with bent-shaped molecules and influence of these surface immobilised molecules on the alignment of bulk liquid crystal (LC) samples has been investigated. Bent-core (BC) compounds containing a dimethylchlorosilane moiety at the end of a terminal alkyl chain and a lateral alkyl chain are successfully attached to transparent conducting ITO substrates in an end-on (ITO-BC-t) and side-on (ITO-BC-l) oriented fashion to create stable permanent self-assembled BC layers on the substrates. Surface functionalization is thoroughly characterised and aligning ability of these BC-modified ITO substrates for orientation of bulk LC sample is evaluated for nematic phase of both rod-like and BCLC samples. The BC-modified substrates are effective in aligning the rod-like compounds in vertical (ITO-BC-t), planar orientations (ITO-BC-l) and the BC compounds in homeotropic (ITO-BC-t) alignment. [ABSTRACT FROM AUTHOR]

Bent-core liquid crystals have set the first example of forming polar superstructures from achiral molecules. Polar switching studies in smectic phases have revealed several exciting sub-phases which have never been observed in rod-like liquid crystals. In this study, mesomorphic and polar switching properties of three bent-core compounds belonging to a homologous series have been investigated using polarizing optical microscopy (POM), differential scanning calorimetry, XRD studies, electro-optics, and dielectric spectroscopy. These achiral, unsymmetrical four-ring bentcore liquid crystals with a polar fluoro substituent at one end and n-alkoxy chain at the other terminal end possess azo, ester, and imine linkages between the four phenyl rings and different lateral substituents. The compounds 16-F and 18-F exhibit orthogonal smectic phase with antiferroelectric polar order, and additionally, the compound 16-F exhibits a short range nematic phase with a polar order. The compound 7-F exhibits broad enantiotropic nematic mesomorphism without appearance of any smectic ordering at low temperature. The smectic and nematic phases were identified by their optical textures observed by POM. Distinct polarization current peaks under triangular wave voltage are observed for all the compounds in the entire mesophase range. Relaxation phenomena corresponding to polar associations of the molecules are observed in dielectric spectroscopy. The cybotactic nature of the nematic phase is established by the XRD and electro-optic studies of 16-F. Although it is rather difficult to form mesophase when the number of aromatic rings is reduced from five, we have successfully demonstrated the bent-core compounds with four-ring which exhibit orthogonal smectic phases as well as nematic mesomorphism with unusual cybotactic signature. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (SWCNTs) are dispersed in (4’-fluoro phenyl azo) phenyl-4-yl 3-[N-(4’-n-hecyloxy 2-hydroxybenzylidene)amino]-2-methylbenzoate (6–2M-F) a bent-core nematic (BCN) liquid crystalline medium composed of bent-shaped molecules with short core, reduced bend angle possessing polar fluoro substituent in longitudinal direction and methyl group in bent direction. Such molecules are at the borderline of typical bent-core and rod-like molecules resembling hockey stick shape with intermediate properties. The elastic anisotropy is negative for 6–2M-F (bend elastic constantK33< splay elastic constantK11); similar to other BCNs reported earlier with smectic-like clusters; but turns to high positive (K33>K11) value by insertion of SWCNT (concentration ≥0.05 wt.%) in 6–2 M-F. The ratio ofK33/K11becomes comparable to the calamitic liquid crystals (LCs) in doped system. Dielectric anisotropy increases in the nanocomposite implying enhanced nematic ordering due toπ–πelectron interaction between CNTs and the LC molecules. Threshold voltage at first increases and then decreases with increasing CNT concentration owing to the respective variations in splay viscosity of the system. The present study demonstrated the interaction of SWCNTs with BCN molecules and reveals significant modifications in viscoelastic, dielectric and ionic properties of the host. [ABSTRACT FROM AUTHOR]

This review article mainly delves into the comprehensive development, thermal stabilization, characteristics, and applications of Blue Phase III (BPIII) derived from non-calamitic, mainly T-shaped and bent-core liquid crystals (BCLC). The discussion begins with discovering and characterizing various liquid crystal (LC) phases of BCLCs, emphasizing the significance of the nematic (N) phase in three and four-ring BCLCs. Following this, the focus shifts to the stabilization, properties, and potential applications of BPIII, particularly those derived from non-conventional (T-shaped and BCLCs) liquid crystals. The review highlights the exceptional electro-optical (E-O) properties of BPIII, including high Kerr constants and distinct phase transitions. Studies reveal the impact of chirality on thermal behavior, microscopic observations, and the influence of molecular structures on mesophase formation. Investigations into asymmetrical chiral liquid crystal diads and hydrogen-bonded complexes underscore the importance of molecular design in expanding BPIII ranges. Furthermore, achiral unsymmetrical BCLC designs reveal significant insights into the interplay between molecular structure, phase transitions, and E-O behavior. Experimental data propose that BPIII operates as a topologically protected liquid featuring skyrmion filaments, highlighting its potential in technological applications. Additionally, the structural transformation and E-O properties of highly polar BCLCs are examined to stabilize BPIII at room temperature, achieving notable Kerr constants and low voltage requirements. These collective studies provide a thorough understanding of BPIII and its promising applications in materials science and technology., (© 2024 Wiley-VCH GmbH.)