Preparation and characterization of mixed alkyl amido complexes of gallium

A series of primary amido gallium alkyl complexes that includes a base free dimer, [^tBu₂Ga(μ-N(H)^tBu)]₂ (1), Lewis base stabilized monomeric complexes, ⁿBu₂Ga(N(H)^tBu)(THF) (2) and ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]py (3) and an anionic complex, ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]₂[Li(Et₂O)] (4) is reported. Complex 1 crystallizes in the triclinic space group P-1 (a = 10.265(5) Å, B = 15.752(6) Å, C = 8.932(4) Å, = 90.32(3)°, β = 105.61(3)°, γ = 88.24(4)°) with two molecules, each residing on an inversion center, in the asymmetric unit. Structural analysis revealed a planar Ga₂N₂ core with both the bridging N and the Ga centers in distorted tetrahedral environments (Ga---C distances 2.052(3)-2.065(3) Å and Ga---N distances 2.060(3)-2.069(3) Å). The use of excess amido ligand allowed the isolation and crystallization of 4. Complex 4 crystallized in the monoclinic space group P21/n (a = 8.666(2) Å, B = 22.305(3) Å, C = 15.570(3) Å, β = 103.47(2)) with Z = 4. The pseudotetrahedral gallium center has a coordination sphere composed of two amido ligands (Ga---N1 = 2.011(8) Å, Ga---N2 = 2.006(7) Å), and two ⁿBu ligands (Ga---C17 = 2.002(9) Å Ga---C21 = 1.985(12) Å). A bridging interaction of the lithium cation with the lone pair of electrons on each of amido nitrogen atoms generates a molecular core which is made up of a planar Ga---N1---Li---N2 distorted square (N1---Gal---N2 94.4°, Gal---N2---Lil 86.2°, N1---Li1---N2 92.2°, Gal---N1---Li1 87.1°).     

Preparation and characterization of a carbon nanotube-lyotropic liquid crystal composite

We present a detailed study on the integration of individual single-walled carbon nanotubes (SWNTs) within a lyotropic hexagonal liquid crystal (LC) for the first time. Two systems are studied in this work; in the first, the same surfactant is used for both the dispersion of the SWNTs and the formation of the LC. In the second system, we use different surfactants for the dispersion of SWNTs and LC formation. Light microscopy imaging combined with small-angle X-ray scattering (SAXS) indicates that the nanotubes (NTs) are well dispersed and aligned along the LC director. The macroscopic property, namely, the viscosity, is strongly enhanced by the presence of the NTs.     

Preparation and characterization of side chain cholesteric liquid crystalline polysiloxanes containing two chiral groups

A series of liquid crystalline (LC) polysiloxanes containing diosgeninyl and menthyl groups (from monomers M ₁ and M ₂, respectively) were synthesized. The chemical structures of the monomers and polymers obtained were confirmed by elemental analysis, Fourier transform infrared spectroscopy, proton NMR and carbon‐13 NMR. The LC properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. Monomer M ₁ showed cholesteric oily‐streak and spiral textures. Copolymers P ₂–P ₅ exhibited cholesteric phases. With increasing concentration of M ₂ units, the glass transition and clearing temperatures decreased. Experimental results demonstrated that a flexible polymer backbone and a long flexible spacer tended to favour a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.     

Preparation and characterization of side chain cholesteric liquid crystalline polysiloxanes containing two chiral groups

A series of liquid crystalline (LC) polysiloxanes containing diosgeninyl and menthyl groups (from monomers M₁ and M₂, respectively) were synthesized. The chemical structures of the monomers and polymers obtained were confirmed by elemental analysis, Fourier transform infrared spectroscopy, proton NMR and carbon-13 NMR. The LC properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. Monomer M₁ showed cholesteric oily-streak and spiral textures. Copolymers P₂-P₅ exhibited cholesteric phases. With increasing concentration of M₂ units, the glass transition and clearing temperatures decreased. Experimental results demonstrated that a flexible polymer backbone and a long flexible spacer tended to favour a lower glass transition temperature, higher thermal stability, and wider mesophase temperature range.     

Determination of the molecular orientation of very thin films on solid substrates: surface liquid crystal layers and rubbed polyimide films

The molecular orientation of very thin films on solid substrates can be determined quantitatively by measuring the polarized infrared (IR) absorption spectra of samples as a function of angle of incidence. The quantitative molecular orientation is derived by fitting the incident angle dependence and the dichroic ratio with theoretical calculations. We applied this method to a technologically important system: liquid crystal (LC)/rubbed polyimide film. To understand the alignment mechanism of LC molecules in contact with rubbed polyimide films, we have quantitatively determined the molecular orientation of rubbed polyimide films and a surface LC layer in contact with a rubbed polyimide film. In this paper two relations are discussed: (1) correlation between the inclination angle of polyimide backbone structures in rubbed films and the pretilt angle of bulk LC in contact with them, and (2) relation among the molecular orientation of a rubbed polyimide film and those of surface and bulk LC layers in contact with it.     

Preparation and characterization of plasma-polymerized styrene thin films

Plasma-polymerized styrene (PPS) thin films (several hundred to several thousand Å thick) have been prepared under a variety of discharge conditions in a tubular reactor inductively coupled to a radio frequency (13.56 MHz) power supply. Studies have focussed on the correlation of deposited polymer structure, evidenced both at the film surface (via XPS analysis) and in the bulk polymer (via transmission FT–IR analysis) with controllable plasma parameters (coupled rf power, monomer flow rate, monomer pressure). It has been determined that the relative number of phenyl rings incorporated into the film intact is an inverse function of the power per styrene molecule ratio. Polymer deposition rate was found to be a strong function of styrene flow rate and substrate temperature. Plausible elements of the styrene plasma polymerization mechanism will be considered.     

Preparation and characterization of a novel polyimide liquid crystal vertical alignment layer

A series of diamines with a side chain containing rigid biphenyl unit and nonpolar alkoxy side end group [4-alkoxy-biphenol-3′,5′-diaminobenzoate] (Cm-BBDA, m = 4, 6, 12) were synthesized and their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and nuclear magetic resonance spectroscopy (¹H NMR). Then three polyimides (PIs) were prepared by copolymerization of pyromellitic dianhydride (PMDA), 4,4′-methylenedianiline (MDA) and Cm-BBDA in N-methyl-2-pyrrolodone (NMP), and chemical structures of all PIs were confirmed by FT-IR. Structural identification of all poly(amic acid)s (PAA) was performed by ¹H NMR. Liquid crystal (LC) cells were fabricated using these PIs as the alignment layer for characterization of the alignment properties of LCs. It was found that the planar alignment was obtained when PI with side chain containing alkoxy side end group of 4 carbon atoms was employed and the vertical alignment was observed when alkoxy side end groups of 6 or 12 carbon atoms were included. A uniform vertical alignment was validated by polarizing microscopy. It was testified that LC vertical alignment possessed high thermal stability.     

Simultaneous calorimetric and optical reflectivity measurements of extremely thin liquid crystal films

Abstract

An extremely sensitive measuring system has been developed to obtain simultaneously heat capacity and optical reflectivity data from thin free-standing liquid crystal films. Results from 3(10)OBC near the smectic A to hexatic B transition will be reported and discussed in the context of recent theory regarding phase transitions in two dimensions.     

Preparation and characterization of mesoporous silica thin films from polyethoxysiloxanes

Tetraethoxysilane (TEOS) and polyethoxysiloxanes (PEOSs; prepared by the acid‐catalyzed hydrolytic polycondensation of TEOS) were subjected to the sol–gel process in the presence of cetyltrimethylammonium bromide (CTAB), respectively. The PEOSs with M_w 700–26,000, as prepared by sol–gel coating of TEOS and PEOS under various conditions, were used. Uniform and crack‐free thin films of thickness 276–613 nm were prepared by spin‐coating of a PEOS solution containing CTAB. When the coating films were sintered at 400 °C, the combustion of ethoxy groups and CTAB took place to provide porous silica thin films. The structure of the thin films was found to be dependent on the molecular weight of PEOS and the molar ratio of CTAB/Si: lamellar or hexagonal phase was observed for M_w less than 15,000 and for CTAB/Si molar ratios greater than 0.10. Honeycomb structures were observed for M_w less than 5000 and for CTAB/Si molar ratios of 0.15. The honeycomb structure was also observed by atomic force microscopy and transmission electron microscope. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2542–2550, 2006     

Preparation and characterization of anthracenecarboxylic acid doped polyaniline thin films

Doped polyaniline films were prepared with electrochemistry method. A small conjugated molecule, anthracenecarboxylic acid(2-ACA), was used as the dopant, considering its electrical activeness due to the conjugated π-π* structure. Film morphology of doped and undoped polyaniline samples was investigated. The corresponding changes in optical and electrical properties after ACA doping were discussed. By measuring and calculating their energy level distribution, a promising application of polyaniline thin films as buffer layer in optic-electric devices is expectable.     

Photoinduced reorientation processes in thin films of photochromic LC polymers on substrates with a photocontrollable command surface

Orientation and reorientation processes that occur in nematic and cholesteric LC polymer systems under irradiation with plane-polarized light are studied. A copolyacrylate containing phenyl benzoate and azobenzene side groups is synthesized as a nematic polymer; the cholesteric mixture is prepared via doping of the nematic copolymer with the chiral dopant, the derivative of D-isosorbide. Thin layers of the azobenzene-containing photoorientant SD-1 are first used as orienting substrates for polymer liquid crystals. Thin layers of the copolymer and of the mixture are spin-coated on the substrate after irradiation of the photoorientant layer with polarized light. It is shown that after annealing phenyl benzoate and azobenzene side groups of the nematic copolymer orient strictly along the direction of orientation of surface molecules, whereas in the case of the cholesteric mixture, a partial formation of the helical structure is observed. It is demonstrated that all the systems under examination can experience the repeated cyclic reorientation of the cooperative type under irradiation and subsequent annealing of the films.     

Preparation and characterization of thin films of SiO(x) on gold substrates for surface plasmon resonance studies

We report here on the fabrication and characterization of stable thin films of amorphous silica (SiO(x)) deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using the plasma-enhanced chemical vapor deposition (PECVD) technique. The resulting surfaces were characterized using atomic force microscopy (AFM), ellipsometry, contact angle measurements, and surface plasmon resonance (SPR). AFM analysis indicates that homogeneous films of silica with low roughness were formed on the gold surface. The deposited silica films showed excellent stability in different solvents and in piranha solution. There was no significant variation in the thickness or in the SPR signal after these harsh treatments. The Au/SiO(x) interfaces were investigated for their potential applications as new surface plasmon resonance sensor chips. Silica films with thicknesses up to 40 nm allowed visualization of the surface plasmon effect, while thicker films resulted in the loss of the SPR characteristics. SPR allowed further the determination of the silica thickness and was compared to ellipsometric results. Chemical treatment of the SiO(x) film with piranha solution led to the generation of silanol surface groups that have been coupled with a trichlorosilane.     

Synthesis and characterization of a metal chelate-bridged quasi-ladder main chain discotic liquid crystal polymer

A metal chelate-bridged quasi-ladder discotic liquid crystal polymer (DLCP) has been prepared by a controlled chelation reaction of cupric ions with β-diketone groups on two adjacent poly(AADK-HMM) chains, synthesized by the hydrosilylation of a bis-allyl groupterminated β-diketone monomer and 1,1,3,3-tetramethylhydrodisiloxane (HMM). X-ray diffraction patterns of the samples annealed in the mesomorphic state or cooled from the isotropic phase demonstrated the existence of an ordered columnar structure on short or long range scales, respectively. The fact that the molecular weight of the cupric complex is approximately twice that of the parent polymer indicates that the quasi-ladder double chain polymer is the predominant product although some terminal defects are present.     

Preparation and characterization of thin films of monomeric and polymeric octacyanophthalocyanines

Thin films were prepared on substrates, cleavage surface of KCl single crystal, and metallic copper, by reaction of 1,2,4,5-tetracyanobenzene with the substrate at various temperatures. The films were characterized by elemental analysis, IR, and UV/VIS spectroscopies. The films were observed by scanning electron microscopy. The films produced on copper at temperatures between 300 and 400°C consisted of copper octacyanophthalocyanine and its polymer with ladder structure. The ratio of polymer to monomer increased with elevating the reaction temperature. The films were composed of ribbon-like crystals. The film produced on copper above 450°C was composed of an amorphous and continuous layer of polymeric copper phthalocyanine. The film produced on KCl at temperatures between 250 and 350°C consisted of potassium octacyanophthalocyanine and its polymer with ladder structure. The film produced on KCl above 450°C was polymeric potassium phthalocyanine. Those films contained more metal content than that required stoichiometrical.     

UV-driven switching of chain orientation and liquid crystal alignment in nanoscale thin films of a novel polyimide bearing stilbene moieties in the backbone

A novel photosensitive polyimide, poly(4,4'-stilbenylene 4,4'-oxidiphthalimide) (ODPA-Stilbene PSPI) was newly synthesized. The most surprising feature of this PSPI is that the PSPI films irradiated with linear polarized ultraviolet light (LPUVL) can favorably induce a unidirectional alignment of liquid crystals (LCs) in contact with the film surface and further switch the director of the unidirectionally aligned LCs from a perpendicular direction to a parallel direction with respect to the polarization direction of LPUVL by simply controlling the exposure dose in the irradiation process. These LPUVL-irradiated films were found to provide high anchoring energy to LCs, always giving very stable, homogeneous cells with unidirectionally aligned LCs regardless of the LC alignment directions. In the films, the PSPI polymer chains were found to undergo favorably unidirectional orientation via a specific orientation sequence of the polymer chain segments led by the directionally selective trans-cis photoisomerization of the stilbene chromophore units in the backbone induced by LPUVL exposure. Such unidirectionally oriented polymer chains of the films induce alignment of the LCs along the orientation direction of the polymer chains via favorable anisotropic molecular interactions between the oriented polymer chain segments and the LC molecules. In addition, the PSPI has an excellent film formation processibility; good quality PSPI thin films with a smooth surface are easily produced by simple spin-coating of the soluble poly(amic acid) precursor and subsequent thermal imidization process. In summary, this new PSPI is the promising LC alignment layer candidate with rubbing-free processing for the production of advanced LC display devices, including LC display televisions with large display areas.     

Synthesis, characterization and crystal structure of 1-ferrocenesulfonyl-2-long carbon chain alkyl benzimidazole

Six new 1-ferrocenesulfonyl-2-benzimidazole derivatives were prepared by the reaction of ferrocenesulfonyl chloride with benzimidazole derivatives in the presence of dichloromethane and n-tetrabutylammonia bromide. The yields of these six new ferrocenesulfonyl benzimidazole derivatives were about 80%. The structures characteristic were confirmed by IR, ¹H-NMR, Elemental analysis and MS. The crystal structure of compound a₂ was determined via X-ray single crystal diffraction and it belongs to monoclinic system with space group C2/c, and the unit cell parameters are α = 2.8252(2) nm, b = 0.97696(7) nm, c = 1.64828(12) nm, α = 90°, β = 92.053(2)°, γ = 90°, V = 4.5466(6) nm³, Z = 8, F (000) = 2024, Mr = 481.40, Dc = 1.407 g/cm³, μ = 0.784 mm⁻¹, R ₁= 0.0495, wR ₂= 0.1517. The results show that the reactions of 2-alkylbenzimidazoles containing active hydrogen with ferrocenesulfonyl chloride gave 1- ferrocenesulfonyl-2-alkylbenzimidazoles in good yields. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(11) (in Chinese)     

Malonate complexes of dysprosium: synthesis, characterization and application for LI-MOCVD of dysprosium containing thin films

A series of malonate complexes of dysprosium were synthesized as potential metalorganic precursors for Dy containing oxide thin films using chemical vapor deposition (CVD) related techniques. The steric bulkiness of the dialkylmalonato ligand employed was systematically varied and its influence on the resulting structural and physico-chemical properties that is relevant for MOCVD was studied. Single crystal X-ray diffraction analysis revealed that the five homoleptic tris-malonato Dy complexes (1-5) are dimers with distorted square-face bicapped trigonal-prismatic geometry and a coordination number of eight. In an attempt to decrease the nuclearity and increase the solubility of the complexes in various solvents, the focus was to react these dimeric complexes with Lewis bases such as 2,2'-biypridyl and pyridine (6-9). This resulted in monomeric tris-malonato mono Lewis base adduct complexes with improved thermal properties. Finally considering the ease of synthesis, the monomeric nature and promising thermal characteristics, the silymalonate adduct complex [Dy(dsml)(3)bipy] (8) was selected as single source precursor for growing DySi(x)O(y) thin films by liquid injection metalorganic chemical vapor deposition (LI-MOCVD) process. The as-deposited films were analyzed for their morphology and composition by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Rutherford backscattering (RBS) analysis and X-ray photoelectron spectroscopy.     

Plasma surface modification and characterization of POSS-based nanocomposite polymeric thin films

The effect of a remote oxygen plasma on nanocomposite hybrid polymer thin films of poly[(propylmethacryl-heptaisobutyl-polyhedral oligomeric silsequioxane)-co-(methylmethacrylate)] (POSS-MA) has been examined by advancing contact angle, X-ray photoelectron spectroscopy (XPS), and variable-angle spectroscopic ellipsometry (VASE). Exposure to a 25 W remote oxygen-containing plasma was found to convert the surface of POSS-MA films from hydrophobic to hydrophilic within 20 s. The exposure time needed for this conversion to occur decreased as the O2/N2 ratio in the plasma environment increased, indicating a positive correlation between the hydrophilicity and the presence of oxygen in the plasma. Local bonding information inferred from high-resolution XPS data showed that the isobutyl bonding to the POSS moiety is replaced with oxygen as a result of plasma exposure. Finally, VASE data demonstrates that increasing the weight percent of POSS in the copolymer significantly impedes the oxygen plasma degradation of POSS-MA films. On the basis of these results, a model is presented in which the oxygen plasma removes isobutyl groups from the POSS cages and leaves a SiO2-like surface that is correspondingly more hydrophilic than the surface of the untreated samples and is more resistant to oxidation by the plasma. The ability to modify surfaces in this manner may impact the utility of this material for biomedical applications such as microfluidic devices in which the ability to control surface chemistry is critical.