Study of Liquid‐Crystalline Phase Changes during Evaporation in Vegetable Oil Emulsions

During evaporation, the rate between volatile and nonvolatile components in an emulsion changes. In this study, emulsions of marigold and canola oil were made according to a phase diagram, simulating the decreasing water amount that happens when the water evaporates from an emulsion. In addition, two basic emulsions were submitted to evaporation and then to microscopic analysis to compare the results of both tests. It was observed that when the water rate decreases, the liquid‐crystalline phase changes its organization, reaching a proportion that it is not hydrated anymore, having a solid aspect. Moreover, these emulsions submitted to evaporation remained to show lamellar phase even when there was no water in the formulation. This is interesting to understand the behavior of an emulsion after it is applied under the skin.     

The Influences of Polymers and Temperature on the Foam Properties of 3‐Dodecylalkoxyl‐2‐hydroxylpropyl Trimethylammonium Chloride

The foam performances of 3‐dodecoxy‐2‐hydroxypropyl trimethylammonium chloride (C₁₂TAC) have been determined in the existence of different relative amount of polymer. The experimental results show that the foaming ability of the mixture systems of the C₁₂TAC/PEG and C₁₂TAC/PVP is stronger than that of the surfactant solutions in the absence of polymer, and with the increase of relative amount of polymer both foaming efficiency and foam stability of the surfactant solutions are evidently enhanced. For the aqueous solution of the surfactant, effect of temperature on foaming properties has also been examined. The results show that both the foaming ability and stability of the foams of the surfactant solutions are highest (or strongest) at 30°C.     

Synthesis and Characterization of Polyimide‐Silica Hybrids: Effect of Matrix Polarity on the Mechanical and Thermal Properties

Polyimide‐silica hybrid materials have been prepared through the sol‐gel process by mixing various proportions of tetraethoxysilane (TEOS) with polyamic acids (PAAs). Two types of PPAs were employed. The first was obtained by reacting an equimolar mixture of oxydianiline (ODA) and pyromellitic dianhydride (PMDA) in dimethylactamide (DMAc) as solvent. The second was prepared using a mixture of ODA and 2,2‐Bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (6F‐OHDA) in molar ratio 9:1, respectively and reacting with a stoichiometric amount of PMDA in DMAc. Polyamic acids were converted to polyimides and a sol‐gel reaction proceeded simultaneously by heating the hybrid films to 300°C. The hydroxyl groups from 6F‐OHDA allows the secondary bonding between the polyimide and growing silica phase and thus retard the gross phase separation. Only the 10 mol% addition of 6F‐OHDA in the polyimide chain resulted in a drastically different microstructure for the resulting hybrids. SEM, stress‐strain analysis, temperature variation of storage and loss modulus, and thermal stability were used to characterize the hybrid materials. Properties of both types of hybrids have been compared and related to the two different types of structures of polyimides used in the preparation of the hybrids.     

Studies on the Syntheses and Properties of UV-sensitive Organosilicon Monomers and Polymers

Photosensitive organosilicon monomers and polymers containing furylacrylate, cinnamate or methacrylate groups were synthesized. The chemical structure of these organosilicon monomers were confirmed by 1H NMR and elemental analysis.The curing rates of these photosensitive polysiloxanes were also determined, all of them show a good UV-sensitivity. The UV-sensitivity of polysiloxanes containing pendent furylacrylates are comparable to that of polysiloxanes with either pendent cinnamate or pendent methacrylate groups.     

Rheologic Properties and Molecular Configuration of Polymers in Salt‐Alkali‐Surfactant Mixed Solutions

With the vacuum sublimation freezing‐drying and rheological techniques, the salt/alkali/surfactant effects on the solution properties and the aggregate conformations of the polymers, synthesized hydrophobically modified poly (acrylamide) (HMPAM), were investigated. The experimental methods included viscosity measurements, the photomicroscopy, scan electron microscopy, and the freeze fracture transmission electron microscopy. The variety of conformations of the ultramolecular aggregates, the hydrophobical region, and the spatial network structures resulted from the hydrophobical interaction were studied. Combined results confirmed that HMPAM could form several of interesting three‐dimensional network structures either in distilled water or NaCl solution. The results have revealed the mechanism of the salt/alkali/surfactant effects on the peculiar rheological properties of the solution.     

Effect of Polycondensation Reaction Conditions on the Properties of Thermotropic Liquid‐Crystalline Copolyester

In this study a range of wholly aromatic copolyesters based on kink m‐acetoxybenzoic acid (m‐ABA) monomer (33 mol%) and equimolar‐linear p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280°C and 260°C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide–angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), hot‐stage polarized light microscopy, proton‐nuclear magnetic resonance analysis (¹H‐NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280°C in 5 h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5–15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160°C and 165°C) in the nematic mesophase. The T_g values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93–126°C. Fibers prepared by a hand‐spinning technique from the polymer melt exhibit well‐developed fibrillar structure parallel to the fiber axis.     

Effect of Emulsification Method on the Properties of Lecithin‐ and PGPR‐Stabilized Water‐in‐Oil‐Emulsions

Water‐in‐oil (w/o) emulsions were prepared with phosphatidylcholine‐depleted lecithin or polyglycerol polyricinoleate (PGPR) as emulsifying agents. The effect of different laboratory emulsification devices and the effect of sodium chloride on particle size distribution, coalescence stability, and water droplet sedimentation were investigated. The properties of lecithin‐stabilized w/o emulsions were found to depend more strongly on the emulsifying method than those prepared with PGPR. The rotor‐stator system was not suitable for preparing stable w/o emulsions with lecithin. Whereas the addition of salt was essential to achieve coalescence‐stable emulsions prepared with PGPR, the presence of NaCl favored the coalescence of water droplets and phase separation in emulsions containing lecithin.     

Studies on the Lanthanum‐Induced Pinacol Coupling of Aromatic Aldehydes and Ketones in Aqueous Media

The pinacol coupling of aromatic aldehydes and ketones was carried out in 16–71% yield using La–36%HAc–CH₂Cl₂ system with stirring at rt in 4 h. The reactions in the same system gave pinacols in 12–91% yield under ultrasound irradiation at rt in 2 h.     

Heat Resistance and Dynamic Mechanical and Rheological Properties of a Blend of Crystallizing Polymers,Polyimide and Copoly(urethane—imide), at Identical Chemical Structure of the Imide Blocks in the Initial Polymers

Russian Journal of Applied Chemistry - A blend of crystallizing polyimide and newly synthesized partially crystalline multiblock (segmented) copoly(urethane—imide), consisting of 75 wt %...     

Aqueous Two‐Phase System (ATPS) Containing Gemini (12‐3‐12,2Br−) and SDS I: Phase Diagram and Properties of ATPS

Two phases coexist in an aqueous system that contains the two surfactants cationic gemini 12‐3‐12,2Br? and anionic SDS. An aqueous two‐phase system (ATPS) is formed in a narrow region of the ternary phase diagram different from that of traditional aqueous cationic‐anionic surfactant systems. In that region, the molar ratio of gemini to SDS varies with the total concentration of surfactants. ATPS not only has higher stability but also has longer phase separation time for the new systems than that of the traditional system. Furthermore, the optical properties of ATPS are different at different total concentrations. All of these experimental observations can be attributed to the unique properties of gemini surfactant and the synergy between the cationic gemini surfactant and the anionic surfactant SDS.     

The Mobility of Threaded α-Cyclodextrins in PR Copolymer and Its Influences on Mechanical Properties

The methylated polyrotaxane(Me PR) copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin(α-CDs) in polyrotaxane(PR) copolymer by CH_3I/Na H. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in Me PR copolymer. The sliding of threaded α-CDs along PEG axis in PR and Me PR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in Me PR copolymer. The frequent and vigorous molecular mobility in Me PR and PR copolymers was also verified by dynamic mechanical analysis(DMA) and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and Me PR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.     

Influence of F and CF3 Groups at the C=C Double Bond on the Structure and Properties of Olefinic‐Series Compounds in the Gas Phase: an ab initio MP2 Study

Ab initio calculations of gasphase fluoroolefins with F or CF₃ groups as substituents at the C=C double bond were performed using secondorder Möller–Plesset perturbation theory (MP2) with the 6–31G^* and augccpVDZ basis sets and full geometry optimization. Geometrical parameters, singleelectron energies, electrondensity distributions, dipole moments, polarizabilities, and hyperpolarizabilities were computed. Variations in the electronic structure of fluoroolefins were analyzed and compared with variations in their physicochemical properties and reactivity.     

Instrumented Macroindentation Techniques for Polymers and Composites – Mechanical Properties,Fracture Toughness and Time-Dependent Behaviour as a Function of the Temperature

An innovative cooling and heating device has been successfully applied to an instrumented macrohardness testing machine in close collaboration with the company Zwick/Roell. The prototype allows the local time-dependent analysis of mechanical properties such as Martens hardness and indentation modulus, as well as fracture toughness and creep and relaxation behaviour at temperatures ranging from −100 °C to +100 °C. On the basis of load–indentation depth, load–time or indentation depth–time diagrams, the indentation behaviour as a function of test speed and/or temperature (which has rarely been done for polymers in the macro-range of loading) depending on matrix and materials composition (amorphous/semicrystalline thermoplastics, epoxy resins, micro- and nanocomposites) has been analysed. Martens-hardness, indentation modulus on the one hand and creep compliance and relaxation modulus on the other have been found to be strongly temperature dependent. Adequate methods of indentation fracture mechanics have been enhanced for polymers and applied to determine the fracture toughness of very different polymer-based materials.     

Ether- and Thioether-Linked Naphthalene-Based Liquid-Crystal Dimers: Influence of Chalcogen Linkage and Mesogenic-Arm Symmetry on the Incidence and Stability of the Twist–Bend Nematic Phase

The twist–bend nematic (N_TB) phase with a heliconical nanostructure of the local director generating symmetry breaking by achiral bent-shaped molecules is a hot topic of current liquid-crystal science. As opposed to the most common methylene-linked dimers, this study demonstrates chalcogen ether- and/or thioether-linked 6-(4-cyanophenyl)-2-naphthyl-based liquid-crystal dimers with symmetric and asymmetric π-conjugated mesogenic-arm structures that exhibit the N_TB phase. Although the symmetric bis(ether)-linked dimer exhibits only the conventional nematic (N) phase, the asymmetric bis(ether)-linked dimer can form the N_TB phase. All thioether-linked dimers form the N_TB phase, wherein the dimers with asymmetric arms vitrify in the N_TB phase on cooling to room temperature. The phase transitions are discussed in terms of the chalcogen linkage combination, mesogenic-arm symmetry, and spacer length. It is revealed that thioether-linked dimers based on asymmetric π-conjugated mesogenic arms with terminal cyano groups are highly beneficial for the realization of materials that form a wide range of N_TB phases and glassy N_TB states at room temperature.     

Chlorine-radical Induced Oxidation of Glyoxal and Glyoxal-S（IV） Adducts in the Aqueous Phase

A laser flash photolysis study of the reactivity of Clwith glyoxal, glyoxal mono- and dibisulfite adducts, 1-hydroxy-2, 2-diol-ethanesulfonate and 1, 2-dihydroxy-1, 2-ethanedi sulfonate in the aqueous phase was carried out. The obtained rate constants can be used for atmospheric modeling.     

Electrochemical and Electrocatalytic Properties of Ferrocene Incorporated in L‐Cysteine Self‐Assembled Monolayers on a Gold Electrode

Abstract

The preparation of a gold electrode modified by aminylferrocene (FcAI) covalently bound to L‐cysteine self‐assembled monolayer (L‐Cys/Au SAM) was described, and characterized by cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS). In pH 7.4 buffers, FcAI incorporated in L‐Cys/Au SAM gave a pair of well‐defined and quasi‐reversible cyclic voltammetric peaks at 0.109 vs. saturated calomel eletrode (SCE), characteristic of Fe(II)/Fe(III) redox couples of the Fc. The apparent surface electron transfer rate constant is 6.86 s^?1 at the modified electrode. The immobilized Fc gave an excellent electrocatalytic activity for the oxidation of epinephrine (EP). The catalytic current of EP vs. its concentration has a good linear relation in the range of 1.7×10^?7–1.0×10^?4 mol/L, with the correlation coefficient of 0.9975 and detection limit of 1.8×10^?8 mol/L. The modified electrode can be used for the determination of EP in practical injection. The method is simple, quick, sensitive, and accurate.     

Effect of Oxygen Redistribution on the Normal and Superconducting Properties of Yttrium High‐Temperature Superconductors

An anomaly is found in the vicinity of T_max 560$ K on electric resistance versus temperature curves for yttrium hightemperature superconductors of the 123 phase. Xray phase analysis suggests a structural phase transition in the vicinity of T_max due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band.     

Temperature‐Induced Swelling and De‐swelling of Thin Poly(N‐Isopropylacrylamide) Gels in Water: Combined Acoustic and Optical Measurements

The temperature‐induced swelling and deswelling of thin layers of poly(N‐isopropylacrylamide) gels in water was measured as a function of cross‐link density and thickness. The collapse behavior was probed via an in situ combination of a quartz‐crystal microbalance (QCM) and a surface plasmon resonance (SPR) spectrometer. The shifts in the SPR coupling angle are explained in terms of decrease of the refractive index inside the film. The evanescent optical wave mostly probes the film's interior properties. The acoustic shear wave emanating from the quartz resonator, on the other hand, propagates to the outer surface of the film, unless the film is very dilute. The acoustic data are dominated by the changes in thickness, rather than in its viscosity. The combination of acoustic and optical measurements, therefore, provides complementary information on the film that can be exploited for sensing applications.     

Recent Developments in Automated Determinations of Trace Level Concentrations of Elements and On‐Line Fractionation Schemes Exploting the Micro‐Sequential Injection—Lab‐On‐Valve Approach

Abstract

The determination of trace level concentrations of elements, such as metal species, in complex matrices by atomic absorption or emission spectrometric methods often requires appropriate pretreatments comprising separation of the analyte from interfering constituents and analyte preconcentration. In this context sequential injection (SI) and lab‐on‐valve (LOV) schemes have proven themselves as superb vehicles to act as front‐end microanalytical methodologies, particularly when employing solid‐phase extraction (SPE) procedures. In this communication, selected SPE‐procedures in the bead‐renewable fashion are presented as based on the exploitation of micro‐sequential injection (µSI‐LOV) using hydrophobic as well as hydrophilic bead materials. The examples given comprise the presentation of a universal approach for SPE‐assays, front‐end speciation of Cr(III) and Cr(VI) in a fully automated and enclosed setup, and the combination of SPE with fractionation schemes of environmentally interesting solid samples (such as soils or sediments) in order to conduct ecotoxicological studies.     

Free Radicals in the Photolysis and Radiolysis of Polymers: IV. Radicals in γ- and UV-Irradiated Wood and Lignin

Free radicals formed in the radiolysis and photolysis of wood and lignin were studied using X-band and D-band EPR measurements. It was found that singlet spectra at g 2, which appeared upon the low-temperature (77 K) - and UV irradiation of wood and lignin, or singlets detected in a posteffect on heating the irradiated samples belong to radicals having conjugated carbon–carbon bonds. Formyl radicals in -irradiated wood and peroxide radicals in - and UV-irradiated wood were detected for the first time using EPR spectra. The radiation-chemical and quantum yields of radical formation reactions were determined. In wood at 77 K, G _R 3.2 1/100 eV and _R 2 × 10^–3.