Polymorphism and mesomorphism of oligomeric surfactants: effect of the degree of oligomerization

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.     

Effect of 1,1,5-trihydroperfluoropentanol and formulations based on it on the structure of oriented polycaproamide fibers

Russian Journal of Applied Chemistry - Polycaproamide fibers, unmodified and modified with 1,1,5-trihydroperfluoropentanol and its formulations with copper diacetate bis(?-caprolactamate) or...     

Effect of electrospinning on the ferroelectric phase content of polyvinylidene difluoride fibers

Polyvinylidene difluoride (PVDF) fibers were prepared by electrospinning from dimethyl formamide (DMF) solutions. The effects of the electrospinning processing conditions on the formation of the alpha and beta phases of PVDF were studied using infrared spectroscopy and differential scanning calorimetry. We have shown that beta-phase PVDF fibers can be electrospun directly from a dimethyl formamide (DMF) solution with a maximum fraction of beta phase, F(beta)max, of 0.75. The fraction of beta phase is found to be greater for smaller-diameter fibers and those spun at an increased voltage.     

Effect of urea on the phase composition and strength of phosphogypsum grains

The effect of urea addition on the composition and strength of grains produced by pelletization of wet phosphogypsum and its subsequent drying was studied experimentally.     

Effect of stationary phase hydrophobicity and mobile phase composition on the separation of carboxylic acids in ion chromatography

In a previous work, we studied the retention behavior of monovalent and divalent carboxylic acids on a highly cross-linked polystryene-divinylbenzene anion-exchange column (IonPac AS4A-SC) using a carbonate-based buffer, and a retention model was applied to the chromatographic data obtained. In this work we characterized the retention of carboxylates (formic, acetic, propionic, lactic, pyruvic, oxalic, malonic, succinic, fumaric, maleic, tartaric, glutaric, adipic, malic, mucic, trans-beta-hydromuconic, trans,trans-muconic acids) on a column with higher hydrophilicity (IonPac AS11) according to analyte and stationary phase properties, using previously investigated eluent compositions and comparing the retention data obtained. Moreover, the effect of organic modifiers (CH3OH and CH3CN) in the eluent on the retention factors was also evaluated. The chromatographic data obtained on the IonPac AS11 column were fitted by the retention model and allowed one to obtain and to compare ion-specific selectivity constants (parameters of the model) with the ones obtained with the previous column.     

Effect of alkoxy terminal chain length on mesomorphism of 1,6-disubstituted pyrene-based hexacatenar liquid crystals: columnar phase control

Synthesis and mesophase-transition behaviors of six 1,6-disubstituted pyrene-based hexacatenar liquid crystals 1_n (n=8–18) are reported here. They were synthesized by the Sonogashira coupling between 1,6-diethynylpyrene and 2-bromothiophene bearing a trialkoxybenzoyl group. The phase-transition behavior was studied by differential scanning calorimetry and polarized optical microscopy; a few mesophase progressions, I–Col/I–X–Col and Col–Sm, were observed, where X was an optically isotropic but unidentified phase. The structures of Col_r, Col_h, and Sm phases were analyzed by the X-ray crystallography, and the effect of the terminal alkoxy chain length on the mesomorphism was evaluated.     

Effect of heat treatment on the properties and structure of TiO2 nanotubes: phase composition and chemical composition

Titanium oxide (TiO₂) nanotubes prepared by electrolytic anodisation of a titanium electrode have been systematically heat treated to control the conversion of the as‐prepared amorphous structure to nanocrystalline anatase and rutile. Raman spectroscopy revealed that the temperature of calcination is critical in determining the structure and crystallinity of the titania. X‐ray Photoelectron Spectroscopy analysis shows the as‐prepared film to consist mainly of oxide, although a small amount of fluoride contamination remains from the electrolyte. Organic components from post‐anodising cleaning treatments were also present. Fluorine ions are gradually ejected from the anodic layer during annealing and the fluorine concentration is negligible in samples that are heat treated above 400 °C. Choosing the appropriate annealing temperature allows the structure to be made up of defined proportions of anatase and rutile with a reduced contamination of species from the electrolyte or organic solvents. Copyright © 2010 John Wiley & Sons, Ltd.     

Templating effect of silk fibers in the oriented deposition of aragonite

Controlled deposition of calcium carbonate crystals can be obtained on degummed Bombyx mori silk fibers through the use of a silk fibroin solution; aragonite crystallites are found on the surface of the fiber with consistent orientation along the longitudinal axis; the results indicate that the combination of the ordered surface structure on the silk fiber and the directing-effect of silk fibroin solution are the key factors in the orientative deposition process of the mineral.     

Effect of degree of saponification on structural and property change of poly(Vinyl alcohol) fibers

To improve the drawability and finally the mechanical properties, poly(vinyl alcohol)s (PVA₈₆, PVA₉₃, and PVA₉₉) with respective degrees of saponification of 86, 93, and 99% were synthesized using solution polymerization. Following the synthesis dimethylsulfoxide (DMSO) solutions of the PVAs were gel-spun into methanol. After extraction of DMSO from the as-spun fibers the dried fibers were first drawn at 120 °C then at 180 °C. An analysis of the structure and properties of the fibers was performed using FT-IR, differential scanning calorimetry (DSC) and a fiber strength tester. The degree of saponification had an effect on the formation and intensity of the intermolecular hydrogen bonds, melting, drawability and strength of the PVA fibers. Low degrees of saponification weakened the intermolecular hydrogen bonds and interfered with the formation of crystallites, causing low melting points and low heat of fusion. Generally, drawing was easier to carry out at lower temperature, and higher draw ratios could be obtained, leading to higher fiber strengths. Copyright © 2003 John Wiley & Sons, Ltd.     

NMR spectrum of phenylacetylene oriented in the nematic phase

The NMR spectrum of phenylacetylene has been studied in the nematic phase of a mixture of 50% 4-methoxy benzylidene 4-amino-α-methyl cinnamic acid-n-propyl ester and 50% anisole-p-azophenyl-n-capronate at 30°C. Ratios of interproton distances have been derived.     

Effect of the mobile phase composition on the retention behaviour of diphenylsilica pre-coated plates

The retention of some rifamycins and steroids on diphenyl bonded pre-coated silica gel plates, in relation to the mobile phase used, was examined by thin-layer chromatography. Neat organic solvents, non-aqueous and aqueous binary mixtures were tested as eluents. By comparison of retention data for rifamycins and steroids, respectively, under non-aqueous and aqueous conditions, a dual retention mechanism on this diphenyl phase was found. Interactions with the residual silanol groups seemed to prevail when employing as mobile phase the more lipophilic solvents tested, such as chloroform or dichloromethane, whereas interactions with the aryl groups of the bonded phase prevailed when using high polarity alcohols or aqueous mixtures. As a consequence, by changing the mobile phase, a large variation in selectivity with a concomitant change in retention order of the test compounds was observed.     

Effect of thermal treatment conditions on the phase composition and structural characteristics of V-Mo-Nb-O catalysts

The formation of an active phase in V-Mo-Nb oxide catalysts for the selective oxidation and ammoxidation of ethane during thermal treatment in air and in helium was studied using high-temperature in situ and ex situ X-ray diffraction analysis, transmission electron microscopy, IR spectroscopy, and the differential dissolution method. It was found that, in thermal treatment below 500°C, the formation occurred through the same irreversible steps with the formation of a unidimensionally ordered layered compound with structure elements like Mo₅O₁₄ regardless of the calcination atmosphere. Above 500°C, the formation of crystalline phases took place; the composition and structure of these phases depended on the atmosphere of thermal treatment. The unidimensionally ordered V-Nb-Mo oxide with structure elements like Mo₅O₁₄ exhibited the best catalytic properties.     

Effect of the mobile phase composition on the adsorption behavior of tryptophan in reversed-phase liquid chromatography

Single-component adsorption isotherm data of l-tryptophan on a C18-bonded silica column were acquired by frontal analysis (FA), with aqueous mobile phases containing 2.5, 5, and 7.5% of acetonitrile (ACN) or 7, 10, 15, and 20% of methanol (MeOH). Most of these isotherms have two inflection points and three different parts. The low and the high concentration parts exhibit langmuirian behavior. The intermediate part exhibits anti-langmuirian behavior. The inflection points shift toward higher concentrations with increasing mobile phase concentration in ACN or MeOH, which causes the differences in the isotherm profiles. The nature of the organic modifier and its concentration affect only the isotherm profile and the numerical values of its parameters, not the nature of the best model, which is the bi-Moreau model in all cases. The isotherm profiles depend on the experimental conditions because they affect the intensity of the adsorbate-adsorbate interactions. Overloaded band profiles of tryptophan were recorded with the seven mobile phase compositions. They were used to determine the best values of the isotherm coefficients by the inverse method (IM) of chromatography. There is an excellent agreement between the values of these parameters obtained by FA and by IM. Increasing the concentration of either ACN or MeOH in the mobile phase causes a slight decrease in the saturation capacities of the low and the high energy sites, and in the adsorption constant of the low energy sites. The adsorption constant of the high energy sites increases with increasing concentration of either solvent or is little affected. The adsorbate-adsorbate interaction constants of both low and high energy sites increase for both solvents. Saturation capacities of the high energy sites are higher for ACN than for MeOH.     

Intrinsic crazing and anisotropy of maximum recoverable extension in oriented glassy polycarbonate

The critical draw ratio for initiation of intrinsic crazing in polycarbonate below the glass transition temperature has been determined after preorientation in the melt. Even when referred to the isotropic state, this ratio is found to depend not only on the extent of preorientation but also to be distinctly anisotropic. Under the assumption that intrinsic crazing occurs at the maximum extension of the entanglement network, these results are incompatible with a strain dependent but homogeneous breakdown of the entanglement network, but can be interpreted in terms of departure from affine transformation of the radius of gyration of an entangled length.     

Modification effects of short carbon fibers on mechanical properties and fretting wear behavior of UHMWPE composites

The present work comparatively studied the modification effects of short carbon fiber (CF) on the mechanical properties and fretting wear behavior of ultra‐high molecular weight polyethylene (UHMWPE)/CF composites. The interactions between CFs and UHMWPE interface were also investigated in detail. The results showed that, with the increase in fiber content, the compressive modulus and hardness of the composites increased, while its impact strength decreased. It was found that filling of CF can reduce the friction and wear of UHMWPE. In addition, the UHMWPE‐based composites reinforced with nitric acid‐treated CF exhibited better mechanical properties, lower friction coefficient, and higher wear resistance than those of untreated UHMWPE/CF composites. This was attributed to the improvement of interfacial adhesion and compatibility between CF and UHMWPE matrix caused by surface chemical modification of CF. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of yttrium oxide on the formation of the phase composition and porous structure of titanium dioxide

The formation of the structure of TiO₂ (anatase) doped with 1–5 mol % Y₂O₃ is reported. The dopant changes the anatase structure from regular to nanocrystalline. The nanocruystalline structure consists of incoherently intergrown 5- to 7-nm anatase crystallites (500°C) separated by interblock boundaries accommodating yttrium ions. The formation of the nanocrystalline anatase structure stabilizes small anatase crystallites and raises the anatase-to-rutile phase transition temperature above 900°C. Owing to this structure, the developed specific surface area and fine porous texture of yttrium oxide-doped titanium dioxide survive up to higher temperatures than those of undoped titanium dioxide.     

Effect of chemically bonded stationary phases and mobile phase composition on beta-blockers retention in RP-HPLC

The effects of stationary and mobile phase on retention of 18 beta-adrenolytic drugs (beta-blockers) have been studied. Four 'deactivated surface' stationary phases (polar-embedded or end-capped) were examined. Special attention was drawn to the cholesterolic (SG-CHOL) and alkylamide (SG-AP) stationary phases, and their application for analysis of the compounds. The retention of analyzed substances was also examined in terms of mobile phase composition. Sixteen different configurations of mobile phases were prepared, all based on methanol and acetonitrile with ammonium acetate and ammonium formate. The difference in retention between ammonium formate and acetate water solutions, and peak shape changes related to the addition of triethylamine (TEA), were investigated. Principal component analysis was used to find the similarities between stationary phases. Polar-embedded phases synthesized on the same sorbent possess very similar properties. All phases based on silica gel compared with the monolithic column also showed similarities in retention of beta-blockers. The addition of TEA to the mobile phase did not influence strongly the retention, and analysis of asymmetry factors showed only a little peak broadening for a few compounds on the monolithic column.     

Proton NMR spectrum of indene oriented in the nematic phase

The proton NMR spectrum of the 8-spin system of indene has been studied in the nematic phase of N-(p-ethoxybenzylidene)-p-n-butylaniline. Orientation parameters and ratios of interproton distances have been derived and are compared with the results of an electron diffraction study.     

The NMR-spectrum of benzaldehyde partially oriented in the nematic phase

The NMR spectrum of benzaldehyde oriented in the nematic phase of a mixture of p-(p-ethoxyphenylazo)phenylheptanoate and p-(p-ethoxyphenylazo)phenylundecylenate is analysed. It is demonstrated that the data are inconsistent with models in which the aldehyde group freely rotates or has minimum energy when it is perpendicular to the ring plane. The barrier height to rotation, however, cannot be obtained, nor is it possible to discriminate between the two possible solutions in which the averaging planar forms do or do not reorient in the liquid crystal between successive internal rotations.