Ying-Gang Jia

Synthesis and phase behaviour of chiral liquid crystalline monomers based on menthyl groups, smectic polymers and cholesteric elastomers

The synthesis of new chiral liquid crystal monomers (M1 −M4 ) derived from menthyl groups, the corresponding smectic polymers (P1 −P4 ), and cholesteric elastomers (E1 −E4 ) based on M2 and crosslinking agent (CA ) is presented. The chemical structures and purity were characterised by Fourier transform infrared, 1H nuclear magnetic and elemental analyses. The phase behaviour and mesomorphism were investigated by differential scanning calorimetry, polarising optical microscopy, thermal gravimetric analysis and X-ray diffraction. The selective reflection of light for M1 −M4 was characterised with ultraviolet/visible/near infrared. The structure–property relationships of M1 −M4 and P1 −P4 were studied. The effect of the content of mesogenic crosslinking units on phase behaviour and mesomorphism of E1 −E4 was discussed. By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, M1 −M4 all showed strong mesomorphism and exhibited an oily streak and focal conic textures of the cholesteric phase, or the broken fan-shaped texture of the smectic C* phase and the platelet texture of a cubic blue phase. P1 −P4 exhibited batonnet textures of the smectic A phase, indicating that the liquid crystal polymers with siloxane chains tended to form a lower order smectic phase. For M1 −M4 or P1 −P4 , the melting temperature Tm , the isotropic temperature Ti and the glass transition temperature Tg increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic units or decreasing spacer length. E1 −E4 exhibited a cholesteric texture because of the introduction of the nematic crosslinking unit. By increasing the content of the crosslinking unit, the general tendency is toward increased Tg and decreased Ti .

Effect of ionic aggregates of sulphonate groups on the liquid crystalline behaviours of liquid crystalline elastomers

A series of siloxane‐based liquid crystalline elastomers containing biphenyl benzoate mesogenic units and ionic Brilliant Yellow moieties was synthesized. The chemical structures and liquid crystalline properties of the samples were characterized by FTIR, 1H NMR, DSC, POM and XRD. The effective crosslink density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. All the polymers displayed a smectic mesophase. It was shown that the glass transition and melting point temperatures of the polymers increased slightly with increasing content of ionic and mesogenic groups in the polymers, while the liquid crystal mesophase region decrease slightly.

Mesomorphic properties of liquid crystalline polysiloxanes and elastomers based on a tri-vinyl crosslinker

A series of crosslinked liquid crystalline polymers and the corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization; their liquid crystalline properties were characterized by DSC, POM and X-ray measurements. The results show that the crosslinking obtained in the isotropic state leads to a reduction of the clearing point (T ) of the crosslinked polymers, as compared with the corresponding uncrosslinked polymers. The crosslinked polymers with low crosslinking density (P–P) exhibit nematic mesogenic phases, as do the uncrosslinked polymers. In contrast, a high crosslinking density leads to the crosslinked polymers P and P losing their thermotropic liquid crystalline phases; they instead exhibit stress-induced orientation.

Synthesis and properties of new (−)-menthol-derived chiral liquid crystal compounds with alkyl or alkoxy terminal groups

ABSTRACT Two series of chiral mesogenic compounds derived from (−)-menthol with varying length of alkyl or alkoxy terminal groups respectively were designed and synthesised. Their chemical structures were characterised by FT-IR and 1H-NMR spectra. The thermal properties and optical textures were investigated by differential scanning calorimetry and polarising optical microscopy. Bragg selective reflection spectra of the compounds with the alkoxy chain in the N* phase were measured by ultraviolet/visible spectrometer. The results showed that the alkyl series homologues melt directly to the isotropic phase on heating and display cubic blue phase and focal conic textures of chiral nematic phase on cooling, whereas the alkoxy series displayed oily streak textures with iridescent colours on heating, and platelet textures of blue phase and focal conic textures were observed on cooling cycles. The chain structure and length of the terminal groups have profound influence on the isotropic temperature and a large odd–even effect is observed for the compounds. The selective reflection colours of alkoxy series shifted to longer wavelength with the increasing of temperature. GRAPHICAL ABSTRACT

The effect of chain length in terminal groups on the mesomorphic behavior of novel (−)-menthol-based chiral liquid crystal compounds with a blue phase

In this study, two series of novel chiral liquid crystal compounds derived from (−)-menthol with different lengths of alkyl or alkoxy as terminal groups were successfully synthesized. Their chemical structure and liquid crystal properties were investigated by various experimental techniques. Series I, except for compound If, exhibits monotropic properties and the whole series II shows enantiotropic mesogenic properties. Both series I and series II display a platelet texture of a BP and a focal conic texture of an N* phase upon cooling. In addition, series II displays an iridescent oily streak texture along with selective reflection upon heating. The selective reflection wavelengths of series II shift to a shorter wavelength region with increasing temperature in the N* phase. For both series I and series II, a pronounced odd–even effect on the clearing temperature is observed when the parity of the terminal chain is varied. Series I with an odd number of terminal chains and series II with an even number have better order.

The effect of terminal alkoxy chain on mesophase behaviour, optical property and structure of chiral liquid crystal compounds derived from (−)-menthol

ABSTRACT Herein, we present the results of our extensive investigations on the synthesis and phase behaviour of nine novel (−)-menthol-based chiral liquid crystal compounds. They possess three phenyl rings and substituted with (−)-menthyl and varying length of n-alkoxy chains at one end. With the aim of exploring the fundamental relationships between molecular structural features and thermal properties, nine terminal n-alkoxy groups from ethoxy to n-octadecaneloxy group in even numbers have been used. A detailed characterisation of their properties was carried out. The characterisation results clearly illustrate that all the series compounds show the thermodynamically stable phases; the shorter chain homologues display only the BPI and N* phases, and the middle ones exhibit BPI, N* and SA* phases while the longer chain members show the BPI, N* and SC* phases. Besides, the BPI appeared in a narrow temperature range because of their thermodynamic disruption. Temperature range of the N* phase narrows when the length of the n-alkoxy tail increases. The reflection peak is shifted towards short wavelength region with increasing temperature due to the winding of the chiral nematic helix in the N* phase. Furthermore, their inherent reflection peak intensities of reflections were gradually weakened. Graphical Abstract

Effect of spacer length on mesomorphic behaviours of chiral liquid crystal compounds containing (-)-menthyl

ABSTRACT A homologous series of new chiral liquid crystal compounds, MnBEB (n = 4–10), was prepared by covalently linking a chiral (–)-menthyl with biphenyl-benzoate via a dicarboxylic spacer of varying length and parity. A combination of analysis methods, such as FT-IR, 1H NMR spectra, differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length and parity of the flexible spacers has a profound influence on the Tm and Tc and a modest odd-even effect is observed for the chiral liquid crystal compounds MnBEB. Only compound M4BEB developed an N* phase with selectively reflection on heating and a blue phase on cooling process. In addition, increasing the length of the flexible spacers tends to narrow the temperature range of the N* phase and widen the smectic phase, moreover, the pitch becomes longer with the spacer increases. GRAPHICAL ABSTRACT

Synthesis and properties of (−)-menthol-derived chiral liquid crystals by introducing adipoyloxy spacer between mesogenic core and chiral menthyl

ABSTRACT A homologous series of new chiral liquid crystal compounds, M6BnB (n = 2, 4, 6, 8, 10, 12, 14, 16, 18), with varying length of n-alkoxy chains at one end, was formed by covalently linking a chiral (−)-menthyl with biphenyl-benzoate via adipoyloxy spacer group. A combination of analysis methods such as Fourier transform infrared, 1H NMR spectra, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length of the flexible terminal alkoxy group has a profound influence on the clearing points (Tiso) and Tiso decrease with the increase of alkoxy chain (n). In addition, increasing the length of the terminal alkoxy group tends to narrow the temperature range of the N* phase and favour the development of chiral smectic C phase. Graphical Abstract