Small angle X-ray scattering study of chiral side chain liquid crystalline polymers in 5CB and 8CB solvents

Small angle X-ray scattering was used to examine the new chiral side chain liquid crystalline polyacrylates (P_4M and P_11M) and their mixtures (2 wt %) in the low molar mass nematogenics 4'-n-pentyl-4-cyanobiphenyl (5CB) and 4'-octyl-4-cyanobiphenyl (8CB). Complementary data were obtained by polarizing optical microscopy. In agreement with previous studies, the mesophases of the bulk polymers show a dependence on the aliphatic spacers linking the mesogenic units to the polymer backbone. Chiral nematic and smectic A₁ phases were observed for the polyacrylates with four (P_4M) and eleven (P_11M) methylene units as spacers, respectively. In solution with 5CB and 8CB, P_4M exhibits an injected smectic phase, whereas P_11M maintains the smectic arrangement already observed in the bulk, with swollen smectic layers. In all the mixtures, layer stability was found to depend on the liquid crystal used as solvent, as well as on the temperature. At temperatures corresponding to the nematic 5CB and 8CB, the coexistence of two mesophases was observed in the mixtures. Moreover, with the liquid crystal solvents in the isotropic phase, microstructures suspended in the solvent matrix containing the liquid crystalline polymer in the smectic arrangement were detected.     

Computer simulation of interactions between liquid crystal molecules and polymer surfaces I. Alignment of nematic and smectic A phases

Results are presented from computer simulations of liquid crystal molecules in contact with polymeric surfaces. These form part of a study of the complex alignment interactions which operate in liquid crystal displays. The liquid crystal molecules considered are 4-n-pentyl-4'-cyanobiphenyl (5CB) and 4-n-octyl-4'-cyanobiphenyl (8CB); the polymeric surfaces simulated were crystalline polyethylene, polypropylene, poly(vinyl alcohol) and Nylon 6. Additional simulations were performed using graphite as a substrate. Polyethylene, poly(vinyl alcohol) and Nylon 6 were all found to induce orientation of the 5CB and 8CB molecules parallel to the polymer chain axes, as would be expected from experimental studies. On the other hand, polypropylene induces many different orientations with no clear preference for either. No evidence was found for the alignment of 8CB molecules on graphite substrates, in disagreement both with experimental findings and the results from previous simulations. The nature of the alignment interactions and possible reasons for the observed discrepancies are discussed.     

Small angle X-ray scattering study of chiral side chain liquid crystalline polymers in 5CB and 8CB solvents

Small angle X-ray scattering was used to examine the new chiral side chain liquid crystalline polyacrylates (P_4M and P_11M) and their mixtures (2?wt?%) in the low molar mass nematogenics 4′-n-pentyl-4-cyanobiphenyl (5CB) and 4′-octyl-4-cyanobiphenyl (8CB). Complementary data were obtained by polarizing optical microscopy. In agreement with previous studies, the mesophases of the bulk polymers show a dependence on the aliphatic spacers linking the mesogenic units to the polymer backbone. Chiral nematic and smectic A₁ phases were observed for the polyacrylates with four (P_4M) and eleven (P_11M) methylene units as spacers, respectively. In solution with 5CB and 8CB, P_4M exhibits an injected smectic phase, whereas P_11M maintains the smectic arrangement already observed in the bulk, with swollen smectic layers. In all the mixtures, layer stability was found to depend on the liquid crystal used as solvent, as well as on the temperature. At temperatures corresponding to the nematic 5CB and 8CB, the coexistence of two mesophases was observed in the mixtures. Moreover, with the liquid crystal solvents in the isotropic phase, microstructures suspended in the solvent matrix containing the liquid crystalline polymer in the smectic arrangement were detected.     

FTIR study of E7 liquid crystal orientations confined to cylindrical cavities of Anodisc membranes

The orientation of E7 liquid crystal (LC) confined within 200 nm diameter cylindrical cavities of Anodisc membranes was investigated by FTIR dichroism techniques. The cavity walls of the confining pores were chemically modified with different length aliphatic acids (C_nH_2n+1COOH, n=5, 6, 7, 9) at 2 and 4% concentrations. From the FTIR spectra of the aliphatic acid-treated alumina Anodsic membranes, we found salt formation between the -COOH group of the aliphatic acids and the Anodisc membranes. From the FTIR spectra of LC-filled Anodisc membranes, we found an abrupt alignment direction change, from parallel to perpendicular, of the LC molecules along the long axis of the cavities between n=6 and n=7 for the 2% concentration of aliphatic acid. However for the 4% concentration of aliphatic acid the parallel to perpendicular alignment direction of LC molecules changed between n=5 and n=6. The same trend was previously observed for ²H NMR measurements by other researchers.     

The effect of polymer chain length on the thermodynamics of acrylate/cyanobiphenyl mixtures

The effect of polymer molecular mass on the phase behaviour and solubility limits of polymer/liquid crystal mixtures is studied for blends of poly(methyl methacrylate) (PMMA) and the small-molecule liquid crystal, 4'-octyl-4-biphenylcarbonitrile (8CB). The phase diagrams from optical microscopy show a limit to the effect of increasing polymer molecular mass. The Flory-Huggins theory (FH) for polymer solutions is used to extract the interaction parameter, χ, from the phase diagrams. The initial FH fits are performed with the assumption that χ is independent of polymer molecular mass, but result in poor correlation to the microscopy data. When χ is allowed to scale with M _w, however, the FH fits are consistent with the limiting molecular mass behaviour. This result represents, to our knowledge, the first time that this scaling behaviour has been observed in polymer/liquid crystal blends. The solubility limit, β, of 8CB in PMMA for each polymer molecular mass is also determined and, when compared with the results of previous studies, support the concept that β is independent of both polymer composition and molecular masses when the polymer molecular mass exceeds ca. 5×10⁵ g mol^-1.     

Discotic Liquid Crystals of Transition Metal Complexes VI. Monotropic Lamella Mesomorphism of Tetrakis(N-Alkyldithiolato)Dinickel(II) and Bis(N-Alkylxanthato)Nickel(II) Complexes

It was found that each of the tetrakis(n-alkyldithiolato)dinickel(II), (C_n-DTA)₄-Ni₂, complexes where n-alkyl is n-pentyl through n-dodecyl, exhibits a broken-fan texture on cooling from an isotropic liquid, and that the phase gave a characteristic lamella structure X-ray diffraction powder pattern. Furthermore, the infrared spectrum of this phase is more similar to that of the isotropic liquid than that of the crystal. Therefore, the phase can be described as a monotropic lamella mesophase. Interestingly, each of the complexes of bis(n-alkylxanthato)nickel(II), (C_n-Xan)₂Ni, (n = 5, 7, 9, 11) exhibits double (triple) melting behavior via the isotropic liquid, whereas each of the complexes of (C_n-Xan)₂Ni (n = 4, 6, 8, 10, 12) shows ordinary single melting behavior. Such unique double melting accompanied by an even-odd effect appears to be the first example of this in the long chain substituted compounds. Each of the complexes of (C_n-Xan)₂ Ni (n = 9, 11, 12) has a monotropic lamella mesophase exhibiting a large broken fan texture.     

The nematic-isotropic two phase region in mixtures of quasi-spherical solutes in alkylcyanobiphenyls: An E.S.R. study using tempone as probe

The transitional behaviour of binary mixtures, each containing a non-mesomorphic quasi-spherical solute at a low mole fraction in a nematogenic solvent, has been investigated by E.S.R. spectroscopy using 4-oxo-2,2,6,6-tetramethyl-4-piperidinyl-1-oxy (tempone) as a spin probe. This approach makes use of the smaller coupling constant obtained for the spin probe in the orientationally ordered nematic phase relative to that obtained in the isotropic phase. The solutes included Et₄C (tetraethylmethane) and R₄Sn (R = C^b2bH₅, n-C_3H7 and nC_b4H₉). The solvents were 4-n-pentyl-4'-cyanobiphenyl (5CB) 4-n-hexyl-4'-cyanobiphenyl (6CB) and 4-n-heptyl-4'-cyanobiphenyl (7CB). This fast approach compares favourably with other studies. In addition it provides the tempone spectral parameter, f, which is a relative measure of the fraction of the nematic phase at different temperatures within the two phase region.     

Investigation of the crystal structure of two amphiphilic diols

The crystal and molecular structures of (R)-4'-(2,3-dihydroxypropyloxy)-4-cyanobiphenyl, 1 and 4'-(cis-cis-3,5-dihydroxycyclohexyloxy)-4-cyanobiphenyl, 5 have been determined. The packing of compound 1 occurs in sheets, with a dense hydrogen bonding network within the layer of one sheet and to the next sheet, whereby the cyano groups are incorporated into the hydrogen bonding network. The hydrogen bonding scheme of compound 5 involves a water molecule; there is some disorder with regard to the hydrogen atoms bound to the water molecules.     

Characterisation of polymerisation-induced phase separation process in polymer-dispersed liquid crystals based on hydroxyalkyl-methacrylate matrices

Hydroxyalkyl-methacrylates are very well-known hydrogel-forming biocompatible polymers. In this work, polymer-dispersed liquid crystals (LCs) based on hydroxyethyl- and hydroxypropyl-methacrylate (HEMA and HPMA) matrices are synthesised and characterised. Two different LCs from the cyano-biphenyl family (4?-pentyl-4-cyanobiphenyl [5CB] and 4?-octyl-4-cyanobiphenyl [8CB]) are used. Polymerisation kinetics, phase transitions, and morphologies generated during the polymerisation-induced phase separation process are analysed. Phase separation is observed at very low conversions, where a polymer-rich phase is initially segregated and this produces an increase in the low-conversion polymerisation rate (ascribed to the auto-acceleration effect of free-radical polymerisations in the polymer-rich phase). The liquid crystalline transition temperature decreases as the concentration of LC decreases, indicating that this phase is impurified. The liquid crystal 8CB is found to be less miscible than 5CB with the polymer matrices, so the LC-rich phase for 5CB is more impurified and its total volume in the material is smaller.     

2H-N.M.R. studies of flexibility and orientational order in nematic liquid crystals

Deuteron magnetic resonance spectroscopy (²H-N.M.R.) has been used to investigate the effect of the nematic environment on the flexibility and orientational order of two perdeuteriated cyanobiphenyl homologues: 4-methyl-4'-cyanobiphenyl (1CB-d₁₁) and 4-n-pentyl-4'-cyanobiphenyl (5CB-d₁₉). The systems studied were low concentrations of 1CB-d₁₁ and 5CB-d₁₉ dissolved in the nematic phases of 5CB, N-(-4-ethoxybenzylidene)-4'-n-butylaniline (EBBA), Merck ZLI-1132 (1132) and a 55wt% mixture of 1132: EBBA. The spectra are dramatically different in these environments. Previous studies on small solutes have suggested that in the 55wt% 1132: EBBA mixture (at 301.4 K) the dominant orienting mechanism depends on the size and shape of the molecule which suggests that it is a short range repulsive interaction. This interaction has been modelled by treating the liquid crystal as an elastic continuum and the solute as a collection of van der Waals spheres which stretch the liquid crystal in the two dimensions perpendicular to the director. The distortion of the liquid crystal depends on the dimensions of the solute, and the elastic energy is described in terms of a Hooke's law force constant, k. The model is extended to include flexible liquid crystal molecules and quadrupolar couplings are calculated for each conformation of the 5CB chain. Statistical averaging over all conformations gives an excellent fit to the experimental spectrum. The results for 1CB and 5CB show that in the other nematic phases contributions from additional mechanisms must be included. Previous studies of ²H₂ and other solutes indicate that the additional mechanism is the interaction between the solute molecular quadrupole moment and the mean electric field gradient of the liquid crystal.     

Synthesis and mesogenic properties of a novel family of oligothiophene derivatives

With the aim of developing new oligothiophene-based liquid crystals involving hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-distearyl-2,2' : 5',2"-terthiophene-5,5"-dicarboxamide (DNC₁₈3T) and N,N'-dialkyl-5,5"-dibromo-2,2' : 5',2"-terthiophene-4,4"-dicarboxamides (DNC_nDBr3T, n = 5, 8, 16, 18), were designed and synthesized, and their thermal behaviour examined. While DNC₁₈3T did not exhibit liquid crystallinity, DNC_nDBr3T compounds with n = 8, 16, 18 were found to form smectic A phases. In addition to liquid crystal behaviour, crystal polymorphism was also observed for DNC₁₆DBr3T. It is shown that both the position of the amido group and the alkyl chain length greatly affect liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of liquid crystal phases in the DNC_nDBr3T system.     

Investigation on lanthanide binuclear complexes of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione and 2,2′-bipyridine

The coordination of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione (BPMPPD) and 2,2′-bipyridine (bipy) with lanthanide ions in water-alcohol solution has been studied. Binuclear complexes of the types : Ln₂(BPMPPD)₃(bipy)₂·nH₂O (n = 2 for Y, n = 4 for Eu, Gd, Dy, Ho, Er, Tm and Yb); Ln₂(BPMPPD)₃bipy·nH₂O (n = 10 for La, n = 3 for Pr, Nd, Sm and Tb) were formed. The compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H NMR spectroscopy, thermogravimetric analysis and fluorescence spectra.     

Sulphur containing mesogens. The mesophasic behaviour of di(4-alkyloxybenzoates) of 4,4'-dimercaptobiphenyl

A homologous series of di(4-alkyloxybenzoates) of 4,4'-dimercaptobiphenyl: CH₃(CH₂)_n-1O-C₆H₄-COS-C₆H₄-C₆H₄-SOC-C₆H₄-O(CH₂)_n-1CH₃,n=1-7, has been synthesized and the thermotropic liquid-crystalline behaviour investigated. All compounds exhibit enantiotropic mesomorphism over a remarkable temperature range. While the mesophase thermal stability is moderately higher than that found for the corresponding oxygenated analogues, the smectic stability is definitely lower. In fact, all the compounds are nematic but smectic mesomorphism (S_C) is observed for n = 7. Compounds with n = 6 or 7 exhibit enantiotropic highly ordered smectic (or disordered crystal) phases, probably S_G in type.     

Hydrogen bonds in the crystal packings of mesalazine and mesalazine hydrochloride

The crystal structures of pharmaceutical product mesalazine (marketed also under different proprietary names as Salofalk, Asacol, Asacolitin, and Claversal) and its hydrochloride are reported. In the crystal mesalazine is in zwitterion form as 5-ammoniosalicylate (1) whereas mesalazine hydrochloride crystallizes in an ionized form as 5-ammoniosalicylium chloride (2). Compound 1 (C₇H₇O₃N) crystallizes in the monoclinic space group P2₁/n with a = 3.769(1) Å, b = 7.353(2) Å, c = 23.475(5) Å, β = 94.38(2)°, V = 648.7(8) ų, Z = 4, D_c = 1.568 g cm⁻³ and μ(MoK) = 1.2 cm⁻¹. Compound 2 (C₇H₈O₃NCl) crystallizes in the triclinic space group P with a = 4.4839(2) Å, b = 5.7936(2) Å, c = 15.6819(5) Å, = 81.329(3)°, β = 88.026(3)°, γ = 79.317(4)°, V = 395.74(3) ų, Z = 2, D_c = 1.591 g cm⁻³ and μ(CuK) = 40.8 cm⁻¹. The crystal structures were solved by direct methods and refined to R = 0.041 for 1 and 0.028 for 2, using 607 and 1374 observed reflections, respectively. The configuration of both molecules, with the ortho hydroxyl to a carboxyl group, favours the intramolecular hydrogen bonds. Very complex systems of intermolecular hydrogen bonds were observed in both crystal packings. They are discussed in terms of graph-set notation. The mesalazine crystal structure is characterized by two-dimensional network of hydrogen bonds in the ab plane. The crystal structure pattern of mesalazine hydrochloride is a three-dimensional network significantly supported by N⁺---HCl⁻ interactions.     

Temperature-driven luminescence switching of europium(III) in a glass dispersed liquid crystal film

Glass dispersed liquid crystal films doped with the tris(β-diketonato)europium(III) complex [Eu(dbm)₃(gly)] (Hdbm=dibenzoylmethane, gly=1,2-dimethoxyethane) were prepared. The liquid crystal host was 4-pentyl-4′-cyanobiphenyl (5CB); a mixed silica–titania glass with a refractive index close to that of 5 CB was chosen as the glass matrix. The photoluminescence intensity was measured as a function of temperature. A strong intensity change was observed at the nematic-to-isotropic transition.     

[C5H5Fe(CO)2]LnCl2·nTHF和[C5H5Fe(CO)2][C5H4(SiMe3)]LnCl·nTHF双核配合物的合成

合成了稀土铁双核配合物:(C₅H₅Fe(CO)₂)LnCl₂·nTHF(Ln=Nd,Sm,Gd;n=1,2)和(C₅H₅Fe(CO)₂)(C₅H₄(SiMe₃))·LnCl·nTHF(Ln=Nd,Sm,Gd;n=0,1,2)。元素分析,热分析,红外光谱和质谱分析确认了这两种配合物。红外光谱数据表明铁与稀土原子是以羰基桥连接。晶体结构分析表明((C₅H₅Fe(CO)₂)Na·4THF是(C₅H₅Fe(CO)₂)LnCl₂·nTHF合成的中间体。     

Synthesis, characterization and antitumor activity of some arylantimony triphenylgermanylpropionates and crystal structures of Ph3GeCH(Ph)CH2CO2SbPh4 and [Ph3GeCH2CH(CH3)CO2]2Sb(4-ClC6H4)3

A series of novel arylantimony(V) triphenylgermanylpropionates with the formula (Ph₃GeCHR¹CHR²CO₂)_nSbAr_(5−n) (R¹=H, Ph; R²=H, CH₃; n=1, 2) were synthesized and characterized by elemental analysis, IR, ¹H-NMR, ¹³C-NMR and mass spectroscopy. The crystal structures of Ph₃GeCH(Ph)CH₂CO₂SbPh₄ and [Ph₃GeCH₂CH(CH₃)CO₂]₂Sb(4-ClC₆H₄)₃ were determined by X-ray diffraction. The in vitro antitumor activities of some selected compounds against five cancer cells are reported.     

Effects of surface chemical properties of activated carbon modified by amino-fluorination for electric double-layer capacitor

We report the synthesis of colloidal nanoparticles with an internal structure forming a gel-like matrix. These nanoparticles are composed of low molecular weight liquid crystal (LC) 4-pentyl-4-cyanobiphenyl (5CB) encapsulated in an LC-based polymer network. Using nanoscopic mechanical analysis, we demonstrate the ability to independently tune the shape anisotropy and stiffness by varying, respectively, the 5CB concentration and the extent of the polymer cross-linking. Based on these data, a model is introduced to account for the effect of the polymer network on the mechanical properties, thus providing novel insight into the nanomechanics of these soft particles.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Structural and spectral studies on N-(4-chloro)benzoyl-N′-(4-tolyl)thiourea

The crystal and molecular structure of the N-(4-chloro)benzoyl-N′-(4-tolyl)thiourea (C₁₅H₁₃N₂OSCl, M_r=304.79) is determined by X-ray diffraction. The crystal structure is monoclinic, space group: P2₁/n, a=16.097(6), b=4.5989(2), c=19.388(7) Å and β=89.299(6)° V=1434.7(9)ų, Z=4. FTIR and NMR spectra have been characterized. The interactions of intramolecular and intermolecular hydrogen bonds have been discussed. Density functional theory (DFT) (B3LYP) methods have been used to determine the structure and energies of stable conformers. Minimum energy conformations are calculated as a function of the torsion angle θ (C13–N1–C14–N2) varied every 30°. The optimized geometry corresponding to crystal structure is the most stable conformation. This has partly been attributed to intramolecular hydrogen bonds. With the basis sets of the 6-311G* quality, the DFT calculated bond parameters and harmonic vibrations are predicted in a very good agreement with experimental data.