Qingbin Xue

Central metal effect on the organization of porphyrin LB films

Monolayers and Langmuir–Blodgett (LB) films of 5,10,15,20-tetra-4-oxy (2-stearic acid) phenylporphyrin (TSPP) and its complexes TSPPCu(II) and TSPPMn(III)Cl have been studied. π–A isotherms show that the molecular areas of the three molecules are similar to one another, while the polarized UV-vis spectra of the transferred films show different tilt angles of macrocycles with respect to the substrates: TSPP, 31°; TSPPCu(II), 0°; TSPPMn(III)Cl, 52°. The UV-vis spectra show that the π–π interactions between porphyrin macrocycles in monolayers of these three porphyrins are different. The Brewster angle microscopy (BAM) observations suggest that the monolayer behavior is also dependent on the central metal ions. These results indicate that the central metal ions have great influence on the organization of the films.

Synthesis and assembly of ordered nanostructures of ZnS, ZnxCd1−xS and CdS nanoparticles at the air/water interface

Parallel nanochains of ZnS and ZnxCd1−xS alloys, and polygonal nanoplates of CdS were prepared at the air/water interface under Langmuir monolayers of 5,10,15,20-tetra-4-oxy(2-stearic acid) phenyl porphyrin (TSPP) at room temperature and characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selective-area electron diffractometry (SAED), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and UV–vis spectroscopy. The results indicate that all the nanostructures are composed of tiny metal sulfide nanoparticles. The formed ZnS and ZnxCd1−xS alloy nanoparticles are cubic zinc blende, and CdS nanoparticles are hexagonal wurtzite nanocrystals, respectively. The formation of the nanochains should be attributed to the self-assembly and aggregation of the cubic zinc blende ZnS or ZnxCd1−xS nanoparticles under the direction of the linear porphyrin supramolecular arrays; while the formation of the nanoplates of CdS should be ascribed to oriented attachment of wurtzite CdS nanoparticles at the interfaces, indicating the large influences of crystal structures on the organization of the nanoparticles and the final nanostructures. After treatment at higher temperature, the nanochains of ZnS and ZnxCd1−xS were preserved with improved crystallinity, while hexagonal and round nanorings composed of CdS nanoparticles appeared.

Monolayers of europium complex mixed with stearic acid and fluorescence properties in Langmuir–Blodgett films

Abstract Monolayers of bis(tri-n-octylphosphine oxide) europium (III) tri(thienyltrifluoro-acetonate) and its mixtures with stearic acid (SA) have been investigated on pure water and a europium complex subphase surfaces. By the observation of Brewster angle microscopy, it was found that homogeneous monolayers were formed by the complex alone and the mixtures with low concentrations of SA, and the complex was squeezed out of the matrix of SA when the molar fractions of SA up to 1:8. Mixed monolayers were successfully deposited onto solid substrate by Langmuir–Blodgett method. The emissions of the complex in the monolayer assemblies mixed with SA indicated that the relative intensity of 5 D 0 → 7 F 2 vs. 5 D 0 → 7 F 1 become higher with the molar fractions of SA, due to the slightly distortion for the complex in the closely packed structure.

Monolayer behaviors for the photochromic liquid crystalline copolymers with azobenzene and cholesterol side groups

Abstract Monolayer behaviors for a series of newly synthesized photochromic liquid crystalline copolymers were studied. Results showed that the azo-homopolymer would aggregate heavily after spreading and its monolayer was not suitable for deposition of the reversible photochromic LB film. However, the liquid crystallinity, which resulted by introducing mesogenic cholesteric side chains, could reduce monolayer aggregation and improve reversible photoinduced structural change in LB films.

Mesogenic structural effects on monolayer behaviors of the liquid crystalline polysiloxanes at the air/water interface

Abstract The monolayer behavior of three newly synthesized side-chain liquid crystalline polysiloxanes and corresponding monomers have been investigated at the air/water interface. The surface pressure-area isotherms and Brewster angle microscopy (BAM) were used to study the influence by different mesogenic units in the side chains. The results indicate that difference in mesogenic unit structure, such as linkage bond and mesogen length, have marked effects on the liquid crystallinity and self-aggregation tendency of the molecular chains which determine the properties of the monolayers.

Studies on the aggregation behaviour of a side-chain liquid crystalline polymer in Langmuir-Blodgett films

Abstract The aggregation behaviour of a newly synthesized ferroelectric side-chain liquid-crystalline polysiloxane (denoted as PSLC) in Langmuir-Blodgett (LB) films has been investigaated. The surface pressure (π)-area ( A ) isotherm and hysteresis experiments for arachidic acid (AA)/PSLC mixed monolayer confirm existence of aggregation or phase-separation during compression. From the UV-Vis spectra, we can clearly see H-aggregate formation. To study the aggregate structure and molecular packing of PSLC, cyclic voltammetry combined with transmission electron microscopy and scanning electron microscopy morphology observations was used. The exciton model previously advanced by Kasha and coworkers is successfully introduced for a qualitative explanation of the spectra observed in the LB films.

Direct observation of 2-D phase transitions of Chiral liquid crystals at the air/water interface

Monolayer morphology of phase transitions and melting process of three low mass weight chiral liquid crystals have been studied and observed in situ by Brewster angle microscopy (BAM). The liquid crystals (LCs) have benzoate benzoyl or biphenyl groups as mesogens and undecenoyloxy as spacer and 2-methylbutyloxy as chiral end group. Their mesogens have different ester bonds in the chemical structure which lead to different bulk phase transition temperatures and gradual change of monolayer phase transition behaviors at the air/water interface due to the strong anchoring effect of the ester bonds with the water surface. Their phase transition behaviors have been discussed according to classical nucleation theory (CNT). Two-dimensional phase transitions for the molecules with multiple ester bonds via two growth process after initial nuclei is initiated: homogenous growth of single domains and coalescence of adjacent domains. Different sizes of the nucleus also indicates the progressive nucleation. MIII with the biphenyl mesogen has the highest transition temperature and the molecules formed aggregates even initially spread at zero surface pressure, the domains accumulated together to form a condensed monolayer during compressing. Melting process of the monolayers of MII and MIII have also been observed at constant surface concentration of molecules.

Monolayer behavior and BAM observaion of biphenyl liquid crystalline polysiloxane at the A/W interface

Monolayers of a chiral biphenyl liquid crystalline polysiloxane and its monomer have been studied by π–A isotherms and hysteresis measurements. Both of them can form monolayers at different temperatures. The molecular packing in the monolayers are temperature-dependent for the monomer but not for the polymer. The molecular orderings are dominated by the packing of the biphenyl mesogens. Metastable monolayers with different ordering and thickness of domains have been directly observed by Brewster Angle Microscopy (BAM) in monomer monolayers. Both of them show characteristics of rigid monolayers. A broken process of the monolayers can be observed during expansion.

Characterizton on the Structure and Ferroelectricity for the LB Film of a Chiral Liquid Crystalline Polysiloxane

Abstract LB films of an newly synthesized chiral SCLC polysiloxane with biphenyl mesogens is prepared to form unique Y-type layer structure. The ferroelectricity of these LB films are measured in sandwich type electrode pattern by Sawyer-Tower method.

Synthesis, characterization of a chiral liquid crystalline polysiloxane and its monomer

Abstract A liquid crystalline polysiloxane and its monomer have been synthesized and characterized by FT-IR and 1HNMR spectra. Their bulk phase liquid crystallinity were studied. The mesomorphic transition behaviors and the mesophases were observed by Differential Scanning Calorimeter (DSC), Polarized Optical Microscopy (POM) and Wide Angle X-ray Diffraction (WAXD) measurements. The monomer showed SmB and SmA phases which are assured by the corresponding broken fan-shaped or mosaic textures and fan-shaped textures by POM observation and WAXD patterns. The polymer had only one mesophase, SmC phase, which showed characteristic of fan-shaped or Schlieren textures by POM and sharp peaks in low angle region and a diffused peak wide angle region from WAXD.