Lyotropic effect in surface charge,electrokinetics, and coagulation of a rutile dispersion

Potentiometric, electrokinetic, and coagulation experiments with a rutile dispersion in the pH region above the point of zero charge exhibit an inverse lyotropic sequence for counterions: Li⁺>K⁺>Cs⁺. The potentiometric and electrokinetic data were interpreted by a surface complexation model assuming the Stern-Gouy-Chapman structure of the interfacial layer, which yielded the values of inner layer capacitances,C, and the intrinsic equilibrium constants,K _ass ⁰ , characterizing the specificity of each counterion. These parameters were used to explain the order of lyotropic sequences in the adsorption, coagulation, and electrokinetic phenomena.     

Structural,thermal, dielectric and optical behaviour investigations of water-free ZnO/lyotropic liquid crystal nanocolloids

ABSTRACT

Zinc oxide (ZnO) nanoparticles of spherical symmetry (average size of ≈ 20 nm) have been synthesised via a non-aqueous lyotropic liquid crystalline (LLC) templating process. Lyotropic liquid crystalline nanocolloids are prepared via dispersing 0.05, 0.1 and 0.5 wt.% ZnO nanoparticles in non-aqueous lyotropic phase. No structural phase change has been seen with the doping of nanoparticles as stable lamellar phases are observed in all the cases. Stability of the lamellar structure and orientation of the ZnO nanoparticles in the liquid crystalline matrix may be attributed to the interfacial surface charge interactions. A significant increase and pronounced dispersion in dielectric permittivity of the ZnO/LLC nanocolloids could be the result of parallel coupling among guest/host, higher dipole- moment of the ZnO nanoparticles and Maxwell-Wagner polarisation. The variation of relaxation parameters has also been discussed and correlated with the dielectric and structural parameters. ZnO/lyotropic nanocolloids devices exhibit dc conductivity of the order of 10^?5S/m owing to the increase in the number of ions (of the order of 10¹⁹m^?3) in the doped systems. Nanocolloids exhibits, the refractive index of range 1.40 to 1.45 and the wide bandgap of the range 4.1–4.5 eV.     

Structural,dielectric and conductivity behaviours of cetyltrimethylammonium bromide/ethylene glycol-based quenched lyotropic mesophases

The present study highlights the effect of quenching on the structural, textural and dielectric dynamics of cetyltrimethylammonium bromide/ethylene glycol binary mixtures of varying concentrations 30:70, 50:50 and 75:25 wt.%. No mesomorphism is seen in the as-prepared binary mixtures as X-ray diffraction and polarisation optical microscopy studies reveal the crystalline-like structures for the studied concentrations. With the effect of quenching, lyotropic hexagonal phase is obtained at 30:70, 50:50 wt.% concentration; however, mixture with higher 75:25 wt.% concentrations exhibit crystalline-like phase. The obtained hexagonal lyotropic phases restrain the mesomorphism up to ≈340 K and then show crystalline-like structures with the further increase in the temperature. Dielectric and relaxation behaviours of hexagonal lyotropic phases are presented in this study. The relaxation parameters of lyotropic phases are also discussed. Interestingly, the hexagonal lyotropic phases obtained for 30:70 and 50:50 wt.% concentrations exhibit ac conductivity of the order of 10^–5 S/m, which can be seen as a significant result of this study.     

The H2-phase of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)benzoate

The phase behaviour of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)-benzoate was investigated by small angle X-ray scattering. The water content of the lyotropic liquid crystal phase was varied between 8 and 20wt% and the investigations were performed in a temperature range up to 70^oC. A reversed hexagonal structure (H₂-phase) as well as the isotropic phase were observed. The lattice constant of the H₂-phase was found to be independent of the water content. An extremely small dependence on temperature could be found. Based on the shape of the molecules and the observed structural properties, a model for the arrangement of the molecules within the H₂-phase is given. The transition temperature from the H₂-phase to the isotropic phase decreases significantly from 60^oC for the sample with 8wt% water content to 30^oC for the sample with 20wt% water content.     

直接模板法合成三维立方介孔氧化硅HOM-5

0引言自1992年Mobil公司制备出M41S系列[1,2](包括MCM-41、MCM-48和MCM-50)介孔氧化硅以来,介孔材料以其有序度高、比表面积大、孔径可调等优异特性,引起了材料科学界的关注。不同类型的系列介孔材料,如SBA[3]、HMS[4]、MSU[5]等相继见诸报道。其中,空间群为Ia3d的MCM-48型三维立方介孔氧化硅具有完全相同,但互不相连的两套孔道[6],贯通性好,对称性高,对物料的传输优于二维孔道结构,在吸附、分离及催化等领域应用前景广泛。但这种结构对应的是溶致液晶相图的V1区域,对于多数表面活性剂来说,此相区较小,因此这种结构较难合成[7]。…     

Determination of the electrochemical diffusion coefficient of methylene blue in SDS/n-C5H11OH/H2O system by non-probe microelectrode voltammetry

The diffusion coefficient of methylene blue (MB) is determined by the method of non-probe microelectrode voltammetry in sodium dodecyl sulfate (SDS)/n-C₅H₁₁OH/H₂O lyotropic liquid crystal system. The results obtained show that the diffusion coefficient of MB increases with water and n-pentanol contents in the microemulsions and the lyotropic liquid crystal but decreases with SDS content. The diffusion coefficient of SDS droplet in the microemulsions and the diffusion coefficient of SDS molecule in the lyotropic liquid crystal with MB all are less than those without MB. The magnitude order of the diffusion coefficient of MB is as follows: the coefficient in the oil-in-water (O/W) microemulsion is greater than the coefficient in the water-in-oil (W/O) microemulsion which is greater than the coefficient in the lamellar liquid crystal (LLC), which is also greater than the coefficient in the Hex.     

Orientational ordering in the nematic phase of 4-alkyl-4'-cyanobicyclohexanes

The orientational ordering of three liquid crystals (trans,trans-4-n-alkyl-4'-cyanobicyclohexanes) has been investigated using ¹³C NMR. 2D proton-encoded local field spectroscopy was used to determine the ¹³C-¹H dipolar coupling constants, from which the order parameters were calculated. Semi-empirical linear relations between the obtained order parameters and anisotropic ¹³C chemical shifts were established. It was found that the order parameters of the major axis of the cyclohexane rings are smaller than those of liquid crystals with phenyl rings, and the order parameters of the C-H bonds in the aliphatic chains also behave differently.     

New liquid-crystalline complex C12DMAO/LaIII with the nematic phase

The results of the synthesis and characteristics of the new lyotropic lanthanide-containing liquid-crystalline systems possessing the nematic phase based on the zwitterionic surfactant, N,N-dimethyldodecylamine oxide (C₁₂DMAO), in the aqueous-decanol environment are presented. The phase diagrams are constructed. The formation of the La-O coordination bonds in the liquid-crystalline complex C₁₂DMAO/La^III is confirmed by IR spectroscopy.     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

Prediction of ternary excess enthalpy data by the UNIFAC Group Contribution method

The UNIFAC Group Contribution method is applied to predict ternary excess enthalpies H ^E . In order to improve previous predictions, values for the group interaction parameters are determined from binary excess enthalpy data. These parameters are used to estimate sixty-four sets of ternary H ^E data which are compared with data from the literature. Results are also compared with those obtained using methods to predict ternary excess enthalpies from the binary H ^E data for the three binary system involved.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Spontaneous formation of hierarchical proton‐conductive structures in sulfonated poly(p‐phenylene terephthalamide) copolymer films

Two partially sulfonated copolymers of poly(p‐phenylene terephthalamide) were studied; the sulfonated diamine to nonsulfonated diamine ratios were x = 1 and x = 2. Polymer solutions in water demonstrated lyotropic liquid‐crystalline behavior, with the critical concentration for nematic phase formation being around 0.7 wt %. Films of these copolymers could be considered for fuel‐cell applications. The in‐plane proton conductivities were of the order of 10^?3 to 10^?2 S cm^?1 between 20 and 90 °C. Increasing the sulfonation level resulted in a more conductive material. Spontaneous alignment of the polymer occurred during film formation, as revealed by X‐ray diffraction. Scattering along the polymer backbone was observed perpendicular to the film, implying that the polymer chains were homeotropically aligned with respect to the film. The average degree of alignment was determined to be 0.66 and 0.77 for x = 1 and x = 2, respectively. Evidence of secondary layering within the plane of the film was seen in SEM images. These layers could provide a pathway for proton conduction to occur within the plane of the film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 666–676, 2007     

Relaxation dispersion and zero-field spectroscopy of thermotropic and lyotropic liquid crystals by fast field-cycling N.M.R.

Abstract

Systematic field-cycling measurements of the T ₁ relaxation dispersion in numerous nematic liquid crystals (azoxybenzenes, Schiff's bases, biphenyls, phenyl-cyclohexanes, cyclo-cyclo-hexanes) confirm our previous observations obtained for PAA and MBBA that order fluctuations of the nematic director are a significant relaxation contribution only at low Lamor frequencies v, i.e. far below the usual megahertz range. Their significance is demonstrated most convincingly by the characteristic square-root dispersion law, T ₁ ～ v ^1/2, which occurs in the kilohertz range and which completely disappears above the nematic–isotropic phase transition. The strength of the collective relaxation mechanism varies by more than two orders of magnitude in the sequence (selection) PAA-d ₈ PAA, PAA-d ₆ PAB, OCB7, MBBA, CB7, PCH7, MBBA-d ₆ MBBA-d ₁₃ and CCH7. This finding can be understood almost quantitatively by the widely differing separations and orientations of proton pairs on the molecules, together with the different viscoelastic parameters of the nematogens. In addition, the underlying slow molecular reorientations have been observed in MBBA and PAA by intensity changes of the zero-field spectra, which are absent for high-field measurements. Similarly, smectic type order fluctuations in layered liquid crystal structures prove to be an effective relaxation mechanism only at low Lamor frequencies. This has been verified by the related linear relaxation dispersion profile, T ₁ ～ v ¹, for both thermotropic systems (TBBA, C₁₂-AA) and lamellar lyotropic mixtures (e.g. potassium laurate in water and phospholipids in water). Our results concerning the time scale of the T ₁ ～ v ^1/2 and T ₁ ~ v ¹ regime do not agree with conclusions drawn from conventional high-field techniques.     

Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by 13C NMR

Abstract

The orientational ordering of three 4′-cyanophenyl-4-alkylbenzoates (with number of carbons in the alkyl chain, n = 6,7 and 8; hereafter abbreviated as n-CPBs) has been investigated by ¹³C NMR. The order parameters of different molecular segments in the nematic phase of the n-CPBs were determined by the two-dimensional technique of separated local field (SLF) spectroscopy combined with off-magic-axis, variable-angle spinning (VAS) of the sample. The carbon-13 chemical shifts for each carbon nucleus in these compounds were determined by slowly spinning the sample parallel to the applied magnetic field. The order parameters obtained from SLF/VAS studies are linearly related to the corresponding anisotropic carbon-13 chemical shifts. These results provide a convenient way to obtain the order parameters for other homologous members of this liquid crystal series by direct measurement of only their carbon-13 chemical shifts in conjunction with the observed linear relationship between order parameters and chemical shifts.     

New lyotropic nematics of double chain surfactants

The phase behaviour of N,N-dialkyl-N,N-dimethyl ammonium bromide double chain surfactants was investigated by polarization microscopy, ²H-N.M.R. spectroscopy, and surface and magnetic field alignment in order to find new lyotropic nematic systems. Decanol was utilized to cause a rod to disc transition in the nematic phase. The sign of the anisotropy of the diamagnetic susceptibility Δx was inverted by substituting the bromide counter-ion with the benzenesulphonate ion. The phase behaviour was modified within a wide range by varying the length of the two alkyl chains. Using these tools we were able to prepare any of the four kinds of uniaxial nematic phases: rod-like and disc-like aggregates with both negative and positive anisotropy of the diamagnetic susceptibility. Several new binary, ternary and quaternary systems of these double chain surfactants and some experiments are described to classify the different nematic phases.     

The use of a lyotropic liquid-crystalline medium and residual dipolar coupling constants for determination of the spatial structure of thiacalix[4]arenes in solutions

The possibility of using an approach for the elucidation of the spatial structure of functionalized thiacalix[4]arenes based on the determination the residual dipolar coupling constants between the ¹H and ¹³C nuclei separated by one chemical bond (¹ D _CH) in lyotropic liquid-crystalline media (poly--benzyl-L-glutamate and CDCl₃) is demonstrated for the first time. This approach was used to distinguish between the cone and 1,3-alternate conformations of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-oxopropyloxy)-2,8,14,20-tetrathiacalix[4]arene. The results were confirmed by the data from 2D NMR (¹H—¹H) NOESY experiments for these compounds in an isotropic solvent (CDCl₃).     

Main‐chain viologen polymers with triflimide counterion exhibiting lyotropic liquid‐crystalline properties in polar organic solvents

The solution‐phase behavior of three main‐chain viologen polymers, which are composed of isomeric xylyl units and triflimide as a counterion, was studied in methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide as solvents microscopically under crossed polarizers. Each of them exhibited a lyotropic lamellar phase in both polar protic and aprotic solvents. Their C^* for the formation of biphasic solutions (1–5 wt %) and concentrations (20–30 wt %) for the lyotropic solutions in methanol was much lower than those in polar aprotic solvents (20–71 and 60–81 wt %, respectively). Their high solubility, high C^* for the formation of biphasic solutions, and high concentrations for the formation of lyotropic solutions in polar aprotic solvents were related to the significant reduction of strong ionic interactions between triflimide and 4,4′‐bipyridinium ions in each of these viologen polymers. They were the first examples of viologen polymers that exhibited a lyotropic phase in polar aprotic solvents. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2015–2024, 2002     

NMR spectra of molecules oriented in a lyotropic mesophase. III—The Spectrum of γ-Hydroxypyridine

Analysis of the ¹H NMR spectrum of γ-hydroxypyridine dissolved in the lyotropic mesophase formed by a 14 : 1 : 1 : 20 mixture (by weight) of sodium dodecyl sulphate, decanol, sodium sulphate and D₂O provides all the spectral parameters with reasonable precision. The chemical shift, the indirect and the direct proton–proton coupling constants are derived. The direct dipolar couplings thus determined are utilised to obtain the relative interproton distances. Information about the molecular orientation and the solvent solute interactions is deduced.     

Lyotropic smectic layering of side-on polysoaps in water

 The synthesis and characterization of lyotropic smectic amphiphilic side-on polymers are described. The amphiphile consists of a rigid, aromatic core with two terminal ethyleneoxide chains of various lengths and is laterally attached to a polysiloxane backbone; the length of the spacer has also been varied. The phase behavior of the monomeric amphiphiles and side-on polymers are determined by polarizing microscopy and ²H-NMR measurements. In water, most of the low molecular weight surfactants show restricted lyotropic properties, namely lyotropic smectic phases. The packing restriction of the amphiphiles is due to their geometric anisometry. All side-on polymers exhibit only lyotropic smectic phases. The phase regime of the polymer mesophase with respect to the monomers depends on the spacer length. In contrast to surfactants having a flexible hydrophobic group, these amphiphiles align spontaneously parallel to an external magnetic field, leading to perfect lyotropic smectic monodomains. Received: 21 May 2001 Accepted: 27 August 2001     

Synthesis and optical properties of triangular gold nanoplates with controllable edge length

Gold triangular nanoplates with a uniform size were synthesized by a simple seeds-growth method in a lamellar lyotropic liquid crystal (LLC) medium consisting of F127, n-C₄H₉OH and H₂O. The edge length of gold nanoplates can be adjusted from tens to several hundreds nanometers (and even a few micrometers) by varying the concentration of Au³⁺ and the seeds solution volume. The optical properties of the synthesized gold nanoplates were studied. The vis-NIR spectra of the synthesized gold nanoplates exhibited a good linear correlation between the in-plane plasmon resonance λ_max and the average edge length of the corresponding nanoplates.

     

Parametric study of the nonisothermal <Emphasis Type="Italic">n</Emphasis><Superscript>th</Superscript>-order distributed activation energy model involved the Weibull distribution for biomass pyrolysis

This paper describes the influences of some parameters relevant to biomass pyrolysis on the numerical solutions of the nonisothermal n ^th-order distributed activation energy model (DAEM) involved the Weibull distribution. Investigated parameters are the integral upper limit, the frequency factor, heating rate, the reaction order and the shape, scale and location parameters of the Weibull distribution. Those influences can be used for the determination of the kinetic parameters of the nonisothermal n ^th-order Weibull DAEM from thermoanalytical data of biomass pyrolysis.