New patterns of twist-bend liquid crystal phase behaviour: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4'-yl)-10-(4-alkylaniline-benzylidene-4'-oxy)decanes (CB10O·m)

Nematic lyotropic liquid crystalline ordering in rhizome powder of Curcuma species and water mixtures: rheological properties and antioxidant applications

This study focuses on developing a self-assembled lyotropic phase in four Curcuma species viz. Curcuma amada (CA), Curcuma caesia (CC), Curcuma Longa (CL), and Curcuma Zedoaria (CZ) using their rhizome powder in an aqueous environment. Polarizing optical microscopy (POM) depicts the maltese cross textures with twisted thread and fractional topological charge of +1/2, which confirms the formation of nematic phases in CA, CC, CL, and CZ/water mixtures along with orientation order parameters 0.34, 0.44, 0.54, and 0.46, respectively. X-ray diffraction (XRD) analysis shows a broad diffraction peak at 2θ ≅ 20°, which further validates the nematic ordering in these mixtures. Fourier transform infrared (FTIR) spectroscopy analysis confirms the inter- and intramolecular hydrogen bonding among keto/enol forms of curcumin and starch molecules with water. Rheological studies demonstrate the shear-thinning behaviour with negative values of power-law exponent n, and strong elastic properties of nematic phases in all the cases. The viscosity of these species varies according to their molecular alignment. Specifically, CL exhibited the highest molecular alignment and viscosity. Nematic lyotropic mixtures are further explored for antioxidant potential through DPPH and phosphomolybdenum assays. The lowest IC50 (25.3 and 26.6, respectively) values for CL-based nematic lyotropic phases are noted for both assays, predicting their best antioxidant potential. The biodegradable and non-toxic nature of Curcuma-based nematic lyotropic liquid crystals (LLCs) offers their potential for advanced material formulations, therapeutic delivery systems, cosmetic applications, and anti-aging formulations, aligning with global trends toward sustainable and green product development.

Mapping the local ambidextrous chirality in thin films of NTB phase by circular dichroism spectra

Circular dichroism mapping (CDM) method was introduced by utilizing the highly collimated light beam of synchrotron radiation (SR) available at Diamond Light Source B23 beamline for scanning the thin films of the NTB phase. We apply SR-CDM to two achiral dimeric materials exhibiting the NTB phase: symmetric DTC5C9 and dissymmetric DTC5C9CB. The SR-CDM measurements directly capture the chiral information in the local NTB domains, providing the ultimate complement to the theoretical predictions of the helical structures: the spontaneous symmetry breaking in NTB phase is ambidextrous. The macroscopic chirality of the NTB phase is determined by the combination of doubly degenerate locally chiral domains in the illuminated area. Additionally, we investigate the temperature dependence, as well as the dynamic nature of the local chirality in the NTB phase by in-situ SR-CDM, confirming a chiral conversion influenced by the state of enantiomeric aggregation and a progressive unwinding of the helical structure in left-handed domains as the crystallization temperature is approached.

Sulfur-linked cyanoterphenyl-based liquid crystal dimers and the twist-bend nematic phase

The synthesis and characterisation of two series of cyanoterphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 34-{ω-[(4'-cyano-[1,1'-biphenyl]-4-yl)thio]alkyl}-[11,21:24,31-terphenyl]-14-carbonitriles (CBSnCT), and the 34-({ω-[(4'-cyano-[1,1'-biphenyl]-4-yl)thio]alkyl}oxy)-[11,21:24,31-terphenyl]-14-carbonitriles (CBSnOCT) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. This is consistent with the widely held view that molecular curvature is a prerequisite for the observation of the twist-bend nematic phase. The nematic-isotropic and twist-bend nematic-nematic transition temperatures are higher for the dimers containing cyanoterphenyl groups than for the corresponding cyanobiphenyl-based dimers. This change is more pronounced for the nematic-isotropic transition temperatures and is attributed to the enhanced interaction strength parameter associated with the cyanoterphenyl fragment whereas the molecular shapes, as governed by the spacer, are rather similar. The behaviour of CBS2CT appears somewhat anomalous and exhibits a higher value of the twist-bend nematic-nematic transition temperature than expected, and this is attributed to the presence of highly bent molecular conformations.

Twist-bend liquid crystal phases and molecular structure: the role of methoxybiphenyl

The synthesis and characterisation of the 4-[{[4-({6-[4-(4-methoxyphenyl)phenyl]hexyl}oxy)phenyl]methylidene}amino]phenyl 4-alkyloxybenzoates is reported. These are referred to using the acronym MeOB6OIBeOm in which m denotes the number of carbon atoms in the terminal alkyloxy chain and is varied from one to ten. All ten members exhibit an enantiotropic conventional nematic (N) phase. In addition, for m = 1-9, the twist-bend nematic (NTB) phase was observed on cooling the N phase. The N-isotropic (I) and NTB-N transition temperatures decrease on increasing the length of the terminal chain and this is more pronounced for the former. This supports the view that the NTB-N transition is predominantly shape driven and this depends largely on the length and parity of the flexible spacer. The transitional behaviour of the MeOB6OIBeOm series is compared with that of the corresponding dimers based instead on a cyanobiphenyl fragment, the CB6OIBeOm series. The rich smectic polymorphism exhibited by the CB6OIBeOm series is extinguished for the MeOB6OIBeOm series. The CB6OIBeOm series shows higher values of the N-I transition temperature than the corresponding members of the MeOB6OIBeOm series whereas the values of the NTB-N transition temperatures are rather similar for corresponding members of the two series. This again suggests that the NTB-N transition is largely shape driven whereas the mixed core interaction plays a more distinct role in driving N phase formation. The promotion of smectic behaviour in the CB6OIBeOm series is attributed to the strong tendency of the cyanobiphenyl fragment to adopt anti-parallel associations.

Liquid Crystal Dimers and the Twist-Bend Phases: Non-Symmetric Dimers Consisting of Mesogenic Units of Differing Lengths

The syntheses and characterisation of the 4-[{[4-({n-[4-(4-cyanophenyl)phenyl]-n-yl}oxy)phenyl]-methylidene}amino]phenyl-4-alkoxybenzoates (CBnOIBeOm) are reported with n=8 and 10 and m=1-10. The two series display fascinating liquid crystal polymorphism. All twenty reported homologues display an enantiotropic nematic (N) phase at high temperature. When the length of the spacer (n) is greater than that of the terminal chain (m), the twist-bend nematic (NTB) phase is observed at temperatures below the N phase. As the length of the terminal chain is increased and extends beyond the length of the spacer up to three smectic phases are observed on cooling the N phase. One of these smectic phases has been assigned as the rare twist-bend smectic C subphase, the SmCTB-α phase. In all the smectic phases, a monolayer packing arrangement is seen, and this is attributed to the anti-parallel associations of the like mesogenic units.