Yuehua Cong

Blue phases induced by rod-shaped hydrogen-bonded supermolecules possessing no chirality or mesomorphic behaviour

A liquid crystalline compound containing (−)-menthol as a chiral centre was prepared and used as a host material, the liquid crystalline behaviour of which were investigated. The host did not exhibit any blue phases on heating and cooling. A series of conventional rod-shaped hydrogen-bonded supermolecules with different terminal chain lengths were synthesized and used as dopants. These supermolecules did not possess chirality or exhibit any mesomorphic behaviour. By adding proton acceptors, proton donors and supermolecules into the host liquid crystal, respectively, the effects of these dopants on the liquid crystalline properties of the mixtures were studied. The formation of blue phases was induced by adding supermolecules into the host liquid crystals. The widest temperature range of the blue phase was about 45 K.

Cholesteric star-shaped liquid crystals induced by a maltose core: synthesis and characteristics

Three esters of maltose (A1–A3) with 4–(4–(alkoxybenzoyloxy)phenoxy) –6–oxohexanoic acid (b1–b3) side-arms have been synthesised. All the maltose derivatives were laevo-rotationary, unlike their parent cores. The side arm b1 did not display liquid crystalline (LC) properties, and b2 and b3 displayed thermotropic nematic LC properties. The star-shaped compound (SSC) A1 with b1 side-arms did not display a mesomorphic phase. Unlike the nematic schlieren texture provided by side-arms b2 and b3, the star-shaped liquid crystals (SSLC) A2 and A3 displayed Grandjean and oily texture in the cholesteric phase. The results suggest that the LC properties of the side-arms have an important influence on the formation of LC properties in an SSC, and that the maltose core is important in determining the mesomorphic phase type. In other words, the SSC displayed LC properties only when the side-arms were also LC, and the maltose core induced a cholesteric phase in the SSLC with nematic side-arms. The mesomorphic regions for A2 and A3 were 39.1 and 53.7°C during the heating cycle and 63.8 and 107.0°C during the cooling cycle, respectively. The longer terminal chain rendered the mesomorphic region broader.

Liquid-crystalline behaviours of novel chitosan derivates containing singular and cholesteryl groups

A series of esters of chitosan with cholesteryl hexanoate and cholesteryl decanoate side chains were synthesised. These compounds had higher solubilities than chitosan itself and all formed cholesteric lyotropic liquid crystalline phases. They had enhanced mesogenic properties as compared with the parent polymer. We consider that these compounds may prove to be of value as vehicles for drug delivery.

Novel fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions

ABSTRACT Novel nematic fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions (Eu-LCI) were synthesised by the use of bis(4-(chlorocarbonyl)phenyl) decanedioate (BD), 4,4-dihydroxybiphenyl (D), 2,5-dihydroxybenzoic acid (B) and anhydrous europium chloride. The chemical structures, liquid crystalline behaviours and fluorescence properties of Eu-LCI were characterised by various experimental techniques. The introduction of small amounts of europium ions endowed the LCI with excellent luminescence properties. POM results showed that europium ions did not change the liquid crystalline texture of the LCI. Fourier transform infrared imaging showed that europium ions were evenly distributed in the matrices of ionomers. A schematic diagram of nematic fluorescent LCI was established to demonstrate the interaction and distribution of the components. Eu-LCI showed reversible mesomorphic phase transitions, wide mesophase temperature ranges and high thermal stability. The thermogravimetric analysis (TGA) results showed that decomposition temperatures (5% weight loss) were greater than 308°C in all Eu-LCI. Eu-LCI can emit red light when excited. The luminescence intensity of Eu-LCI gradually increased with increase in Eu(III) ions from 0.3 to 1.5 mol%. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase, where the fluorescence intensity of Eu-LCI decreased monotonically with increase in temperature. GRAPHICAL ABSTRACT

Synthesis and characterisation of biodegradable liquid crystal elastomer with the property of shape recovery

ABSTRACT Novel shape recovery biodegradable liquid crystal (LC) elastomer is reported here for the first time. The method of synthesis of the shape memory biodegradable LC elastomer has been explored. During the reaction, the LC molecules are added to form LC polymers, and then cross-linking agent is added to form a cross-linked LC elastomer. The LC elastomer in this work is hydrophilic. In vitro degradation of the LC elastomer films in a buffer of pH 7.4 at 37°C shows that the LC elastomer has good degradability. The biodegradable LC elastomer exhibits liquid crystalline behaviour and has shape memory ability. Its shape memory and actuating properties also have been studied. The reversible transition from liquid crystalline phase to isotropic phase is utilised as the switching mechanism for these stimuli-responsive materials. When reheating the LC elastomer to 120°C, the shape will recover. Graphical Abstract

Preparation and characterisation: PSCLC film doping with FexNiy nanoparticles

In recent years, modified liquid crystal (LC) material has been widely applied in display industry for outstanding performances by changing the prescription or adding additives. Polymer stabilised cholesteric liquid crystal (PSCLC) was designed with the aim for achieving better performance. In this study, a stable system was established by doping FexNiy nanoparticles into a PSCLC film, in which nanoparticles (NPs) were modified by organic LC molecules. The NPs composite were monodispersed evenly in PSCLC film without agglomeration. The electrical-optical performance was improved in different ways. The minimum reported response time of FeNi, FeNi3 and Ni was 3.32, 3.45 and 4.32 ms, which showed 72.33%, 71.25% and 64% reduction, respectively. However, the drive voltage of FeNi, FeNi3 and Ni was 6.92, 6.58 and 6.84 V which showed 61.56%, 63.44% and 62% reduction, respectively. The viewing angle of PSCLC was extended. Besides, as the drive frequency was raised by 5 kHz, Vth dropped from 6.58 to 1.62 V, and decreased by 75.37%, which presented the great potential in the frequency drive mode.

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, 1 H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.

Covalent modification of reduced graphene oxide by chiral side-chain liquid crystalline oligomer via Diels–Alder reaction

A effective way for covalent modification of reduced graphene oxide (RGO) by a chiral side-chain liquid crystalline oligomer (CSLCO) is firstly established. CSLCO consists chiral mesogenic units, non-mesogenic units with carboxyl groups and nematic mesogenic units with conjugated diene structure, the properties of materials should be determined by their structures. The conjugated diene structure can be grafted onto the RGO surface via Diels–Alder (DA) reaction, the chiral mesogenic units would enable CSLCO to have optical rotation and the carboxyl groups are expected to constitute coordination bonds with nano titanium oxide (TiO2) to fabricate composites. Spectroscopic tools (Raman and XRD) are used to confirm the completion of the DA reaction. Fourier transform infrared imaging system is utilized to analyze the dispersibility of RGO in the RGO–CSLCO composites. Due to the excellent thermal property of RGO and the interactions between RGO and CSLCO, the dispersed RGO can increase the glass transition and the decomposition activation energy of CSLCO. RGO can enhance the photocatalytic degradation of TiO2 due to its high electron mobility and large specific surface area. By preventing the aggregation of TiO2 and RGO, the CSLCO covalently modified RGO is better than pure RGO to enhance the photocatalytic degradation efficiency of TiO2.

Multistable polymer stabilised cholesteric liquid crystal: exceeding reflection limit in visible region

Cholesteric liquid crystal (CLC) with helically aligned molecules, demonstrates unique optical features. Conventionally, such structure reflects a maximum 50% of unpolarised light. Polymer-stabilised CLC was designed to exceed the limit by mixing liquid crystal (LC) and a photopolymerisable monomer of opposite chirality. The reflectance was carefully investigated and the result was 55.7% in the visible region at room temperature, where it exceeded the theoretical limit. Such phenomena were studied and theoretical model was discussed. Electro-optical test showed the driving voltage was of LC cell was slightly changed after polymerisation.

Synthesis and characterization of liquid crystalline epoxy and co-polymerisation with a non-mesomorphic epoxy resin

ABSTRACT A novel liquid crystalline epoxy resin based on the imine group was synthesised and structurally characterised by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The mesogenic behaviour of the monomer was measured by differential scanning calorimetry (DSC) and polarised optical microscopy (POM), and presented various textures in the extensive temperature range. Methyl nadic anhydride (MNA) was employed to cure the liquid crystalline epoxy resin and the curing process was investigated using POM and wide-angle X-ray diffraction (WAXD). Information about distribution of liquid crystalline epoxy resin in the blending system resulted from the FT-IR Imaging System, indicating that molecules of liquid crystalline epoxy resin can agglomerate to form anisotropic domains. The improvement in mechanical properties of diglycidyl ether of biphenol A (DGEBA) modified with liquid crystalline epoxy was achieved. Scanning electronic microscopy (SEM) showed that an extremely rough and highly deformed fracture surface can be obtained. DGEBA modified with liquid crystalline epoxy resin was characterised by dynamic mechanical analysis (DMA) for its thermal properties. The results indicate that the presence of the liquid crystal phase influences glass transition temperature (Tg). GRAPHICAL ABSTRACT