Effect of degree of acetylation and solvent on the chiroptical properties of lyotropic (acetyl) (ethyl) cellulose solutions

(Acetyl) (ethyl) cellulose (AEC) polymers with an ethyl degree of substitution (DS) of 2.5 and acetyl DS ranging from 0 to 0.5 dissolve readily in a wide range of organic solvents and form chiral nematic liquid crystalline phases in concentrated solution. The chiroptical properties of these liquid crystals are strongly influenced by the acetyl content and solvent. In dichloromethane, dibromomethane, chloroform, bromoform, m-cresol, acetic acid, and aqueous phenol, the AEC lyotropic mesophases all show a handedness inversion as the acetyl DS of the polymers is increased, changing from left- to right-handed supermolecular helicoidal structures. The temperature dependence of the pitch for these mesophases is also reversed from negative to positive with increasing acetyl DS in all the above solvents except aqueous phenol, in which the corresponding AEC mesophases change from positive to negative. The optical microscopic, optical diffraction, and ORD evidence provide a unique indication that the reversal of the handedness and temperature dependence for the AEC mesophases occurs at a compensated degree of acetylation, DA^*. The corresponding compensated mesophases show an infinite pitch and behave optically like nematic mesophases. The value of the DA^* is dependent on solvent. In dichloroacetic acid, AEC liquid crystals remain right-handed, independent of the acetyl DS. At given concentration and temperature, the long pitch samples flow much more readily than short pitch samples. © 1994 John Wiley & Sons, Inc.     

The liquid-crystalline properties of selected cellulose derivatives

The liquid-crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4-methoxyphenylacetoxy cellulose (4MPAC), and p-tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t-butyldimethylsilyl cellulose (TBDMSC), are reported. Hot-stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH₂Cl₂. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid-crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.     

The chiroptical properties of a new liquid-crystalline polymer: (trityl)(pentyl)cellulose

The chiroptical properties of a new liquid crystalline polymer, trityl pentyl cellulose (TPeC), are discussed. This polymer forms lyotropic liquid-crystalline phases in tetrahydrofuran and chloroform. The cholesteric twist sense is right handed in both solvents. The dilute solution optical activity of the phenyl chromophores, measured by circular dichroism (CD), showed no evidence of the exciton splitting expected for a helical arrangement of chromophores. The sign and magnitude of the CD signals were found to change considerably upon mesophase formation.     

The thermotropic and lyotropic liquid-crystalline properties of acetoacetoxypropyl cellulose

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid-crystalline phases. DSC and hot-stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ₀ of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x-ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ₀ for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.     

Mesomorphic and luminescent properties of side chain nematic liquid-crystalline polymers containing Ir(III)

Iridium-containing liquid-crystalline polymers were obtained by graft copolymerisation using poly(methylhydrogeno)siloxane, 1-methyl-4-(4-(4-vinylcyclohexyl)cyclohexyl)benzene (M₁) and an iridium complexes monomer (Ir-M₂). The series of polymers contained different molecular fractions of Ir-M₂ from 0% to 1.2%. All of these polymers showed mesomorphic behaviours. The introduction of small amount of iridium ions endowed liquid-crystalline polymers with luminescent properties. The chemical structures were characterised by IR and ¹H NMR. The mesomorphic properties and phase behaviour were investigated by differential scanning calorimetry, thermal gravimetric analysis, polarising optical microscopy and X-ray diffraction. With an increase of iridium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) decreased. All polymers showed typical nematic marble textures, which was confirmed by X-ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of iridium complexes units did not change the liquid-crystalline state of polymer systems. With Ir³⁺ ion contents ranging between 0.6 and 2.4 mol%, luminescent intensity of polymers gradually increased.     

Effect of chain length and asymmetry on material properties of bilayer membranes

Dissipative particle dynamics is used to extract the material parameters (bending and area stretch moduli) of a bilayer membrane patch. Some experiments indicate that the area stretch modulus of lipid vesicles varies little as the chain length of the lipids composing the bilayer increases. Here we show that making the interactions between the hydrophilic head groups of the model amphiphiles proportional to the hydrophobic tail length reproduces the above result for the area stretch modulus. We also show that the area stretch modulus of bilayers composed of amphiphiles with the same number of tail beads but with asymmetric chains is less than that of bilayers with symmetric chains. The effects on the bilayer density and lateral stress profiles of changes to the amphiphile architecture are also presented.     

Effect of chain length on transfection properties of spermine-based gemini surfactants

The synthesis and associated structure-activity relationships for gene transfection of a series of spermine-derived cationic gemini surfactants incorporating diamino acid headgroups and either identical (symmetrical) or different (unsymmetrical) lipophilic tailgroups is described. Transfection activity is found to depend critically upon the structural elements present.     

Thermotropic liquid-crystalline polymers. XXVII. Reentrant nematic phase of side chain liquid-crystalline polymers and their optical properties

The phase diagrams of side chain liquid-crystalline acrylic copolymers with cyanobiphenyl mesogenic groups are described. These copolymers are shown to form a reentrant nematic phase. The main regularities of the reentrant behaviour of polymer systems are studied. Certain peculiarities of the electric field induced orientation phenomena are discussed.     

Volume shrinkage and abrasive wear properties of crosslinked Poly(ester-urethane-acrylate)/MMA copolymer: Effect of chain length

The current study deals with the preparation of novel crosslink transparent poly(ester-urethane-acrylate)/methyl methacrylate (TPEUMA) copolymers and the effect of hydroxyl terminated aromatic polyester (PEs) was also investigated. The properties of TPEUMA were investigated in terms of double bond concentration, polymerization shrinkage, abrasive wear analysis and chemical resistance. The volume shrinkage decreased due to the significant reduction in the concentration of double bonds. The first two effects reflect in lowering the abrasive wear resistance properties at room temperature, while the larger chain length between crosslink decreases the hardness. Decrease in polymerization shrinkage shows more condensed microstructure which was revealed by the abrasive wear rate of TPEUMAs due to hydrogen bonding near to crosslink point. Increase in the chain length of PEs, decreases the glass transition temperature of TPEUMA copolymer which results in loose microstructure. Worn surface were studied using scanning electron microscope to give insight on the wear mechanism of TPEUMA crosslink. It can be suggested from the present study that this copolymer can be used for a broad range of optical applications.     

Solution properties and chain conformation characteristics of cellulose tricarbanilate

Fractions of two cellulose tricarbanilate samples were characterized by light-scattering (weight-average molecular weight, second virial coefficient, mean-square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ^?1, chain diameter d, and shift factor M_L) were evaluated. The molecular-weight dependence of the mean-square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second virial coefficients.     

Accurate determination of the degree of substitution of long chain cellulose esters

The determination of the degree of substitution (DS) of fatty acid cellulose esters with alkyl chain lengths from C8 to C18 was performed by direct transesterification with trimethylsulphonium hydroxide (TMSH) using tert-butyl methyl ether (MTBE) as a solvent. Transesterification was demonstrated to be quantitative at 75 °C in 60 min. The quantification of the formed fatty acid methyl esters was performed by gas chromatography (GC). After the optimization of the method, long chain cellulose esters (LCCE) could be analyzed in a wide range of DS. The obtained values were compared to those given by other existing protocols. LCCE with DS-values in a range of 5 × 10⁻⁵ to 3 were analyzed with high accuracy. Reproducibility is weakened for high DS values if the sample has a compact aspect limiting the accessibility of TMSH to the ester functions. This method can also be suitable for the analysis of mixed cellulose esters.     

Thermotropic liquid-crystalline properties of extended viologen bis(triflimide) salts

A series of extended, symmetric viologen triflimides were synthesised by the metathesis reaction of lithium triflimide with the respective viologen tosyalates in methanol. Their chemical structures were characterised by Fourier Transform Infrared, ¹H and ¹³C Nuclear Magnetic Resonance spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and variable temperature X-ray diffraction. The viologen salts containing alkyl chain of two carbon and three carbon atoms were relatively low melting salts. Those of alkyl chains of four carbon and five carbon atoms formed ionic liquids at 88 and 42°C, respectively. Those of alkyl chain of 9, 10 and 11 carbon atoms were high melting salts, as high as 166°C. Those of higher alkyl chains of 16, 18 and 20 carbon atoms showed thermotropic LC phases forming SmC, SmA and an unidentified smectic (SmX) phases, and showed SmA to isotropic transitions at high temperatures. As expected, all the viologen triflimides had excellent stabilities in the temperature range of 338–365°C.     

外缘烷基链长对共轭有机小分子聚集行为及光电性质影响

改变分子化学结构和调控分子结构聚集态行为从而影响或改变材料的化学和物理性质, 是开发新型高效有机光电功能材料的重要手段. 在共轭有机分子外缘引入烷基链一般是为了改进材料溶解性能, 但近来的一些研究表明, 烷基链长对一些共轭有机小分子固态聚集行为和光电性质具有重要影响, 烷基链扮演着显著调控材料光电性质的“功能基团”作用. 本文以聚集诱导发光（aggregation-induced emission, AIE）/聚集强化荧光（aggregation enhanced emission, AEE）发射共轭有机小分子为重点, 对近年来有关烷基链长对共轭有机分子聚集形态和光电性质影响的一些典型事例进行评述, 旨在使人们在进行共轭有机分子设计合成及其结构与性能关系研究中能够关注烷基链的因素, 使烷基链变化作为功能导向晶态共轭有机材料设计合成及其可控制备的一种手段.     

Kinetics of polyesterification: Effect of diol chain length

Kinetics of polyesterification of maleic anhydride with polyethylene glycol (PEG) of varying molecular weights have been evaluated. The investigations have been carried out by employing heating cycles comparable to those employed in industrial processes and under nonisothermal conditions. The rate of reaction was found to decrease with increase in the chain length of the polyether. The energy of activation was estimated as 26.91, 40.25, and 47.30 Kcal/mol for PEG of molecular weights 200, 300, and 400, respectively. © 1994 John Wiley & Sons, Inc.     

Critical influence of the alkane length in surface and liquid-crystalline properties of perfluorodecyl-n-alkanes

Differential scanning calorimetry (DSC) measurements together with texture observation with polarizing microscope revealed the presence of a smectic phase for shorter homologues. Film forming properties of all the perfluorodecyl-n-alkanes synthesized here at the air-water interface were thoroughly investigated. Nearly all the compounds investigated were found to be capable of Langmuir monolayer formation when spread at the water-air interface, apart from semifluorinated alkanes (SFA) containing short hydrogenated moiety (n < 10), which partially dissolve in the water subphase. The investigated homologous series of SFA can be divided into four groups, regarding their liquid-crystalline and surface properties. The first group includes molecules with n = 6-10, which form smectic phases in the bulk and do not form stable monolayers at the free water surface. SFA containing 11 or 12 hydrogenated carbons belong to the second group, forming smectic phases at elevated temperatures, which transform into 3D ordering upon cooling. These molecules are found to form Langmuir monolayers of intermediate stability. The remaining groups contain perfluorodecylalkanes with n > 12, which differ in their calorimetric properties; however, both form very stable films on the water surface and do not exhibit liquid-crystalline properties.     

Microemulsions: Effect of alkyl chain length of alcohol and alkane

In microemulsions consisting of four components, i.e. detergent — water — oil — cosurfactant, the free energy of transfer from the continuous oil phase to the interfacial region for the cosurfactant is reported. From the effect of temperature on the free energy, the entropy and the enthalpy values are also reported. The effect of chain length of the alcohol (cosurfactant) is also described. It is further shown, that if the oil phase consists of hexadecane, then the free energy changes as a linear function of the number of carbon atoms in the cosurfactant. On the other hand, if the oil phase is benzene, the cosurfactant chain length has very little effect. These data are analyzed with respect to the microemulsion structure and stability.     

Effect of the chain length on the thermal and analytical properties of laterally biforked nematogens

Three laterally substituted liquid crystals were synthesized in order to investigate the effect of a lateral biforked chain on the thermal and analytical properties. The mesogenic molecules have the same core containing four aromatic rings connected by two ester and one diazo linkages, they differ by the length of one chain within the lateral biforked substituent. The phase transition temperatures were obtained by polarized light microscopy and differential scanning calorimetry (DSC). The clearing temperature and the nematic range decrease with increasing length of the lateral biforked chain. The stationary phases derived from these nematogens provide excellent resolution of various classes of compounds, including aromatic hydrocarbons (AH), substituted benzenes, polycyclic aromatic hydrocarbons (PAH), phenols and volatile organic compounds (VOC) present in the essential oils. The selectivities of the stationary phases were found to decrease according to the length of the side chain.     

Synthesis and liquid-crystalline properties of 4-(heptyloxy)-n-(aryl)benzaldimin-2-ols

The synthesis and liquid-crystalline properties of 4-(heptyloxy)-N-(aryl)benzaldimin-2-ols have been described. The compounds obtained have smectic and nematic mesomorphism. Alternation of the bleaching temperatures (T_bl) with variation of the length of the alkyl radical in the N-aryl fragment has been noted. The dependence of T_bl on the contribution of the substituent to the polarizability of the molecule ² is expressed by the equation T_bl=9.7+1.7².Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1997–2001, September, 1989.