Dodecyltrimethylammonium bromide–disodium dodecanephosphonate mixed micelles

 The aqueous catanionic system dodecyltrimethylammonium bromide (DTAB)–disodiumdodecanephosphonate (DSDP) was studied by potentiometry, conductivity, surface tension, spectrometry and dye solubilization. No precipitation of neutral salts was found in the entire range of compositions studied. Up to four transitions were detected. The first transition, at about 0.001 mol dm⁻³, was probably related to a state change in the adsorption monolayer at the air/water interface. The second, at about 0.0065 mol dm⁻³, was probably related to the formation of ion pairs. The third transition was the critical micelle concentration which was analyzed with the pseudophase separation model and regular solution theory. The interaction between DTAB and DSDP molecules in micelles was weaker than in other cationic–anionic surfactant mixed micelles. Large, probably rodlike, micelles formed at the fourth transition at higher surfactant concentration. No vesicles or lamellar liquid crystals were detected. The adsorbed monolayer at the air/water interface was also studied by means of regular solution theory. It was much richer in DTAB than the micelles and the intermicellar solution. The interaction between DTAB and DSDP molecules at the air/water interface was very low. The results were explained on the basis of steric factors. Received: 6 January 1999 Accepted in revised form: 13 April 1999     

Ion-beam irradiation effects on polyimide-UV–vis and infrared spectroscopic study

Ion-beam irradiation effects on polyimide, Kapton™, were studied with respect to optical and electronic properties. Stack films of Kapton™ (12.5 μm thick) were irradiated to various ion beams in air or vacuo at room temperature and subjected to ultraviolet–visible (UV–vis) spectroscopy, and change in absorbance and energy gap is discussed. The UV–vis absorption spectrum, which is assigned to the transition of electrons in benzene rings from π to π* orbital, upon He²⁺ (6 MeV/u) irradiation in air, shifted towards longer wavelength direction for all cases, and the shift was more obvious for higher linear energy transfer (LET) ion beams. The energy gap of the transition was estimated, and the H⁺ and He²⁺ ion beams caused little change in the transition energy gap Eg, while the heavier ions such as C⁶⁺ and Si¹⁴⁺ caused more significant decrease. This decrease is assumed to the structural changes around benzene rings, and the infrared spectroscopy revealed breakage in imide groups next to benzene ring in the repeating unit of polyimide.     

Optical absorption in solution processed thin films of calcia–alumina binary compounds

UV–visible optical spectra were obtained at room temperature in air for solution-processed thin films of 12CaO·7Al₂O₃(C12A7) on the MgO <100> single crystal substrates after the post-deposition heat treatment at 1,100 °C. Two absorption peaks were observed at 5.3 and 6.1 eV and their presence was attributed to the complex electronic structure of C12A7 and its different energy levels due to the extra-framework species and the framework itself. The peak at 5.3 eV is believed to be associated with O²⁻-Cage Conduction Band type transition whereas the Framework Valence Band to Framework Conduction Band transition is responsible for the peak at 6.1 eV. The nature of electronic transition was found to be direct from the analysis due to Tauc’s law.     

Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data

A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order (m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air.     

Nitrogen-doped mesoporous carbon nanospheres loaded with cobalt nanoparticles for oxygen reduction and Zn–air batteries

Mesoporous carbon supported with transition metals nanoparticles performs desired activities for oxygen reduction reaction (ORR) and clean energy conversion devices such as Zn–air batteries. In this work, we synthesized N-doped mesoporous carbon loaded with cobalt nanoparticles (CoMCN) through self-assembly method. There are sufficient mesopores on the carbon substrate which stem from the pore-forming agent. These mesopores can provide enough accessible active sites and profitable charge/mass transport for ORR. The high content of pyridinic and graphitic N is beneficial for promoting O₂ adsorption and reduction. The smaller value of I_D/I_G indicates the higher degree of graphitization of CoMCN, providing better electronic conductivity. The half-wave potential of CoMCN is 0.865 V in basic solution, which is 24 mV more positive than that of the commercial Pt/C (0.841 V). In addition, CoMCN performs excellent methanol tolerance and stability under both basic and acidic conditions. The Zn–air battery assembled with CoMCN performs the larger power density and open-circuit voltage than the commercial Pt/C-based battery, indicating the potential application in energy conversion systems. This work provides thoughtful ideas for fabricating transition metal nanoparticles based porous carbon for electrocatalysis and metal–air batteries.     

Curing of Divinyl Triethylene Glycol Bis-<Emphasis Type="Italic">o</Emphasis>-phthalate Films in the Presence of Photoinitiators

The film-forming properties of divinyl triethylene glycol bis-o-phthalate in air in the presence of a redox system and β-diketonates of transition metals were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 658-661.Original Russian Text Copyright © 2005 by Mironovich, Nikozyat’, Ivashchenko.     

Fluorinated transition alumina with Al2−x/3O3−xFx compositions: Thermal, chemical, structural and morphological investigations

Fluorinated transition aluminas (Al_2−x/3O_3−xF_x) with hexagonal platelet shape were synthesized via decomposition of α-AlF₃ under air; they are thermally stable up to 1000 °C and exhibit at 1150 °C a weight loss with volume reduction caused by fluorine departure corresponding to a phase transition toward corundum alumina. The different characterizations performed in this study are structural (XRD), chemical (TGA-MS and microprobe analysis) and morphological (SEM, TEM and dilatometry). The evidence provided from this study is consistent with the formation of an Al-O-F phase as an intermediate compound in the pyrohydrolysis of an aluminium trifluoride phase to α-Al₂O₃.     

A qualitative skin layer formation mechanism for membranes made by dry/wet phase inversion

Optimized membranes made by a dry/wet phase inversion process using forced-convective evaporation consist of an ultrathin and pore-free skin layer supported by a nodular transition layer underlying open-cell, sponge-like substructure. It is suggested that the out-ermost region of such case membranes undergo phase separation by spinodal decomposition in the initial stages of the evaporation process. As a result of the small scale of phase separation present in polymer?solvent systems, an appreciable capillary pressure occurs in the interstitial space filled with the polymer-poor phase in contact with air. The resulting force acts normal to the membrane–air interface, which tends to consolidate the polymer-rich phase to form a nonporous surface layer. © 1993 John Wiley & Sons, Inc.     

HNO自由基与O2反应机理的理论研究

采用密度泛函理论(DFT)和从头算方法,在B3LYP/6-311++G(d,p)水平上对反应HNO+O_2做了理论计算研究。优化得到了反应物、中间体、过渡态和产物的几何构型以及相应的能量值、振动频率。通过分析反应路径的能量差异,以及异构化难易程度,发现HNO+O_2反应有2种产物通道:HOONO和HNO_3。其中过氧亚硝酸HOONO是主要产物,有3种稳定的构象。     

Polymers containing 9-alkylcarbazol-3,6-diyl and different aromatic amino groups in the main chain

A series of novel polymers based on 9-alkylcarbazol-3,6-diyl and different aromatic amino groups were synthesized in good yields through modified Ullmann coupling reactions. The resulting polymers were characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. These polymers possess high thermal stability with onset decomposition temperatures of 320-355 °C. Their glass transition temperatures range from 154 °C to 250 °C. The ionisation potentials of the synthesized polymers established by electron photoemission in air technique are in the range 4.95-5.12 eV.     

Studies of structures of poly-ε-caprolactam/montmorillonite nanocomposite: Part 2. Tests of annealed specimens

Using the novel version of thermomechanical analysis (TMA) method, a poly-ε-caprolactam (PA6) and its nanocomposite (PNC) containing 1.6 wt.% of montmorillonite (MMT) were examined. Several disc specimens of those as investigated in the first part of this article were then melted, annealed, and sheared at a rate of 0.5 s⁻¹ engendering ca. 140% strain at 240 °C in a rotational rheometer, and next solidified in ambient air. In PNC as in PA6 specimens prepared in the same way, an amorphous isotropic structure in the surface layer up to 0.5 mm thick was identified, with topological regions differing in thermal expansion properties and related a state of order. This finding differs from other tests, which detect a high level of crystallinity. Probably, it is related with small thickness of the tested layer of material and kinetics of solidification in ambient air.An increase in the free volume fraction, V_f^TMA, evaluated as equal to 3ΔαT_g (Δα is the difference in linear thermal expansion coefficients below and above the glass transition temperature T_g) and resulted from melting, annealing, shearing, and next solidification in ambient air was observed. It suggests that these operations introduce into the specimen some amount of gases (e.g., evaporated water absorbed when cooling) what increases thermal expansion over high-temperature transition of the high-temperature topological region. It means that V_f^TMA is a sum of all voids within a specimen tested (not only a real free volume) independently on their origin. Because of this, it is better to term it as micro or nanoporosity.     

Plasticizer-assisted bonding of poly(methyl methacrylate) microfluidic chips at low temperature

As an important phthalate plasticizer, dibutyl phthalate (DBP) was employed to decrease the bonding temperature of poly(methyl methacrylate) (PMMA) microfluidic chips in this work based on the fact that it can lower the glass transition temperature of PMMA. The channel plates of the PMMA microchips were fabricated by the UV-initiated polymerization of prepolymerized methyl methacrylate between a silicon template and a PMMA plate. Prior to bonding, DBP solution in isopropanol was coated on PMMA covers. When isopropanol in the coating was allowed to evaporate in air, DBP was left on the PMMA covers. Subsequently, the DBP-coated covers were bonded to the PMMA channel plates at 90 °C for 10 min under pressure. The channels in the complete microchips had been examined by optical microscope and scanning electron microscope. The results indicated that high quality bonding was achieved below the glass transition temperature of PMMA (∼105 °C). The performance of the PMMA microfluidic chips sealed by plasticizer-assisted bonding has been demonstrated by separating and detecting ionic species by capillary electrophoresis in connection with contactless conductivity detection.     

The synthesis and thermal properties of polyepichlorohydrin side-chain liquid crystal polymers

The synthesis and characterization of a new series of side-chain liquid crystal polyepichlorohydrin (PECH) polymers are described. The structures and thermal properties of the synthesized polymers were investigated using IR, NMR, polarized optical microscopy and differential scanning calorimetry. A substantial increase of the glass transition temperature with the degree of substitution of side-chain groups was observed. Polymers with a degree of substitution of side groups, of at least 60%, exhibited thermotropic liquid crystalline behaviour. The polymers present thermal liquid crystalline behaviour and form Schlieren and thread texture upon cooling from the isotropic phase, after annealing for 120 min at different temperatures. In addition, the thermal decomposition of PECHOPhPhCN was studied by thermogravimetry under both nitrogen and air environments. The temperature of the maximum decomposition rate was about 340 °C. Weight loss decreased considerably after 350 °C and was approximately 98% at 700 °C. Chemical modification of functional polymers offers a simple method for obtaining liquid crystalline polymers whose transition temperature can be tailored by varying the amount of substitution, however complete substitution cannot be achieved.     

Influence of polishing time on thermo-oxidation characterization of isothermally aged PMR-15 resin

The effect of polishing time on measured oxidation thickness and elastic modulus of isothermally aged PMR-15 neat resin was investigated. A specimen aged 956 h in ambient air at 288 °C (550 °F) was selected for this study. Thermo-oxidation of the specimen results in a surface oxidation layer with different stiffness and polishing characteristics than the interior of the specimen. The specimen was repolished at consecutive time periods from a quick polishing time to extensive polishing time. A white light interferometer was used as a surface profiler to measure height variations from the specimen edges into the interior of the material. Subsequently, optical microscopy and nanoindentation experiments were conducted to correlate observations of oxidation thickness and elastic modulus measurements with polishing time. The modulus profiles obtained from nanoindentation experiments indicate formation of an outer brittle layer followed by a sharp drop in the transition region to the unoxidized interior. The oxidized material is polished at a greater rate than the unoxidized material. The maximum variation in the surface profile from polishing was limited to 5 μm across the oxidation layer (∼150 μm), which results in a slope of ∼2° over the oxidized region. Optical measurements of thickness of oxidized layer and transition region are in good agreement with the height and modulus profiles obtained using the interferometer and nanoindenter, respectively. Results from three techniques show that the measured oxidation thickness and elastic modulus are relatively independent of the polishing time.     

Highly phenylated poly(aryl ether phthalazine)s

Two series of novel amorphous poly(aryl ether phthalazine)s have been prepared via an intramolecular ring closure reaction of poly(aryl ether ketone)s (PAEKs) with hydrazine monohydrate. Fluorinated PAEKs, which display solubility in solvents incorporating a ketone functionality such as acetone or ethyl acetate, were converted to poly(aryl ether phthalazine)s to observe if these polymers would display similar solubility characteristics. The poly(aryl ether phthalazine)s have glass transition temperatures in the range of 278–320°C and show 5% weight loss points greater than 500°C in air and nitrogen atmospheres. The fluorinated poly(aryl ether phthalazine)s were not soluble in ketonic solvents. A series of poly(aryl ether phthalazine)s incorporating pendant 2-naphthalenyl moieties has been prepared in an attempt to produce amorphous, thermally stable polymers with high glass transition temperatures. The polymers have glass transition temperatures in the range of 287–334°C and show 5% weight loss points greater than 500°C in air and nitrogen atmospheres. Poly(aryl ether phthalazine)s undergo an exothermic reaction above the glass transition temperature. The major product of this reaction is a rearrangement of the phthalazine moieties to quiazoline moieties, however some crosslinking of the polymers occurs. Cured samples of the poly(aryl ether phthalazine)s show a small increase in the polymer T_g and are insoluble in all solvents tested. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1897–1905, 1996     

New aspects of migration and flame retardancy in polymer nanocomposites

Annealing of pristine polypropylene blended with the organomontmorillonite (OMMT) at temperatures of 180-340 °C under a stream of nitrogen and of nitrogen-air mixtures is investigated. The oxidative annealing brings about the dispersion of the OMMT in the polypropylene and the formation of a nanocomposite structure. This is evidenced by the increase in the interlayer distance ‘d’ as measured by small angle XRD, with time of annealing and with the weight percent of air. This indicates progressive intercalation of the polymeric matrix into the clay gallery and subsequently exfoliation. The degree of exfoliation is estimated by the extent of migration determined spectroscopically on the surface of the annealed sample. The accumulated clay on the surface due to migration hinders the penetration of the oxygen into the annealing melt as expressed by the decrease in the rate of migration with the increase in the air concentration. This indicates the increase in ageing and storage stability of nanocomposites with increase in the extent of migration. The extent of migration is proportional to the polar carbonyl groups formed on the matrix. The energy of activation of the migration was found to be 37.82 kJ/mol indicating that the rate-determining step of migration is diffusion controlled reaction. The penetration of oxygen into the melt is the first of five steps, followed by oxidation, intercalation, exfoliation and migration. Monitoring the migration with increase in the temperature enables the observation at 275 °C of the transition of the nanocomposite structure to noncolloidal microcomposite. Increasing the annealing temperature above 300 °C brings about a slow, low-temperature combustion and formation of a new kind of char on the surface of the sample.     

A table‐top PXI based low‐field spectrometer for solution dynamic nuclear polarization

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of ¹H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced ¹H signal at 288 kHz was constructed with Litz wire. The largest observed ¹H enhancements (ε) at 6.7 mT for ¹⁴N‐CTPO radical in air saturated aqueous solution was ε~65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi‐frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.     

Wetting reversal transition in phase-separated polymer mixtures

We investigate a wetting reversal transition in thin films of two-phase mixtures of poly(ethylene-propylene) (PEP) and its deuterated analogue (dPEP) on a substrate covered by a self-assembled monolayer (SAM) whose surface energy, _γSAM, is tuned by varying the SAM composition. As _γSAM increases from 21 to 24 mJ/m², a transition from a three-layer (air/dPEP/PEP/dPEP/SAM) to a two-layer (air/dPEP/PEP/SAM) structure occurs at increasing T_c - T, where T_c and T are the critical and transition temperatures, respectively. As the system structure changes from three-layer to two-layer, the thicknesses of the dPEP-rich wetting layers at the air/mixture and mixture/SAM interfaces are found to smoothly increase and decrease, respectively, while the thickness of the PEP-rich layer (ca. one half of the total film thickness) does not change. The dependence of the transition temperature on _γSAM is predicted by a simple model using the experimental data on the surface energies of PEP/dPEP and estimates of the interfacial energy between PEP and dPEP.     

Influence of a cooling rate on a structure of PA6

The structure of the plate specimens obtained from the molten PA6 that was cooled at rates between 2 and 2000 °C/min have been studied. The cooling rate of 2000 °C/min did not ensure a complete amorphization of the specimens. The amorphous phase created by supercooling is unstable and at room temperature undergoes a noticeable cold crystallization. The access of water to the specimen from the surrounding air accelerates this process.Variations in the cooling rate of the melt reflect in rearrangement of the amorphous phase of PA6. Owing to the effect of interaction with the crystalline phase, the amorphous regions undergo changes in molecular weight and MWD of the chain segments between junctions in topological regions, temperatures of the glass transition and β-relaxation, compaction, etc.     

New doped Li-M-Mn-O (M = Al, Fe, Ni) spinels as cathodes for rechargeable 3 V lithium batteries

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M _x Mn_{1− x} CO₃ (M = Fe, Ni; x = 0.08−0.15) or Al _x Mn_{1− x} (CO₃) (OH) _y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure. Received: 25 November 1997 / Accepted: 28 January 1998