Organic halide-alcohol interactions: Observation by means of the glass transition

The glass-transition temperature (T _g) in binary mixtures of the primary alkanols with CBr ₄ and CHBr ₃ has been measured as a function of composition. The results are compared with earlier studies on alkanol solutions of organic chlorides. The initial molar slope (IMS) of theT _g vs. composition curve at the pure alkanol indicates formation of a 1:1 halide-alkanol complex stabilized by a specific halogen-oxygen interaction. The IMS values decrease in the order CBr ₄ >CHBr ₃ >CCl ₄ >CHCl ₃ >CH ₂ Cl ₂ , reflecting decreasing stability of the complex.     

Measurement and modeling of the glass transition temperatures of multi-component solutions

Protein crystals are usually grown in multi-component aqueous solutions containing salts, buffers and other additives. To measure the X-ray diffraction data of the crystal, crystals are rapidly lowered to cryogenic temperatures. On flash cooling, ice frequently forms affecting the integrity of the sample. In order to eliminate this effect, substances called cryoprotectants are added to produce a glassy (vitrified) state rather than ice. Heretofore, the quantity of cryoprotectant needed to vitrify the sample has largely been established by trial and error. In this study, differential scanning calorimetry (DSC) was used to measure the melting (T_m), devitrification (T_d) and glass transition (T_g) temperatures of solutions with a range of compositions typical of those used for growing protein crystals, with the addition of glycerol as cryoprotectant. The addition of cryoprotectant raises the T_g and lowers the T_m of bulk solution thereby decreasing the cooling rates required for vitrification of protein crystals. The theoretical T_g value was calculated using the apparent volume fraction using the Miller/Fox equation extended for multi-component systems. The experimental values of T_g were within approximately ±4% of that predicted by the model. Thus, the use of the model holds the promise of a rational method for the theoretical determination of the composition of cryoprotectant requirement of protein crystallization solutions.     

Glass-forming composition regions and glass transition temperature in nonaqueous electrolyte solutions

With an interest in assessing the suitability of various nonaqueous solutions for electrolyte studies in the viscous region of the liquid state, the glass-forming properties of solutions of calcium nitrate dissolved in various nonaqueous solvents have been determined and compared with the corresponding aqueous solution properties. Solutions in dimethyl formamide prove of particular interest. The composition dependence of the glass temperature is similar in all solvents at high salt contents. Ideal glass temperatures, estimated from thermodynamic data for the pure solvents, are compared with experimental or extrapolated values.     

Debye type dielectric relaxation and the glass transition of alcohols

Many hydrogen-bonded liquids, especially glass-forming cases, display a dielectric relaxation behavior that differs qualitatively from that of other simple liquids. The majority of models aimed at explaining this unusual dielectric behavior associate the prominent Debye process with structural relaxation, viscous flow, and the glass transition. We perform dielectric and calorimetric studies of glass-forming mixtures of 2-ethylhexylamine and 2-ethyl-1-hexanol across the entire composition range. The kinetic glass transition temperature derived from the large dielectric Debye peak decreases, whereas that of the much smaller and asymmetrically broadened peak increases upon addition of amine. Only the latter feature coincides with the calorimetric glass transition results, implying that molecular structure and dielectric polarization fluctuate on time scales that can differ by orders of magnitude in many hydrogen-bonding liquids.     

Electrical conductivity study of the self-association of ionic surfactants in solution in ethyleneglycol,formic acid and formamide

The self-association of several cationic surfactants has been investigated by means of solubility and electrical conductivity measurements in ethyleneglycol, formic acid and formamide. Operational critical micelle concentrations (CMC_op) have been obtained from the vs. surfactant concentrationC plots by the usual interpolation procedure. It has been found that for the surfactant-solvent systems investigated the value of CMC_op increases with the extent of theC-range investigated. This result together with others concerning the effect of temperature and surfactant chain length reveal that the CMC_op-values have an ambiguous meaning concerning the surfactant self-association. Comparison of the vs.C plots for cetyltrimethylammonium chloride and tetramethylammonium chloride, for instance, reveals that some surfactant self-association takes place, probably leading to small, highly ionized surfactant aggregates, but the systems do not show true critical micelle concentration. Solubility measurements as a function of temperature lead to the same conclusion. The results are discussed according to our present understanding of the process of micellization and the necessity of using solvents of very high cohesive energy density in order to observe, with ionic surfactants, true CMCs corresponding to a highly cooperative association process. This appears to be the case only with water and hydrazine, not with formamide and other less cohesive solvents.     

Gas chromatographic indicator of the ability of five- and six-membered heterocyclic nitrogen-containing compounds for self-association in pure liquids

The retention indices of five- and six-membered nitrogen-containing heterocyclic compounds (pyrrole, pyrazole, imidazole, 1,2,4-triazole, pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, isoxazole, and oxazole) were determined on a capillary column with the OV-101 nonpolar stationary phase. The difference between the experimentally determined boiling point of the sorbate and that calculated from GC data (δT _b.p.) was proposed as a gas chromatographic indicator sensitive to the ability of substances to form self-associates in pure liquids. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 730–733, April, 1999.     

Electrodeposition of silver from dense gaseous solutions of silver nitrate in ammonia

Abstract

Silver was electrodeposited on platinum electrodes from solutions of AgNO₃ in NH₃ at temperatures from ?70°C. to 140°C. The solutions were 0.036 molar in AgNO₃ at ? 78°C. In the dense gaseous region, the concentrations of AgNO₃ and NH₃ were 0.018 and 22 moles/liter respectively.

The deposit was observed to become more and more crystalline in appearance as the temperature approached the critical temperature of NH₃(133°C). All electrodeposits at temperatures above 133°C were characterized by either dendritic or needle-like growths on sharp edges and corners. These were not observed at lower temperatures. Both three- and four-sided symmetries were observed, suggesting that the deposits were growing in the [111] and [100] directions, respectively.     

On the relationship between microhardness and glass transition temperature of some amorphous polymers

On the basis of microhardness (H) data measured at room temperature only for a number of polymers in the glassy state, a linear correlation between H and the glass transition temperature T_g has been found (H = 1.97T_g − 571). By means of this relationship, the deviation of the H values from the additivity law for some multicomponent and/or multiphase polymeric systems can be accounted for. The latter usually contains a liquidlike soft component and/or phase with T_g below room temperature. A completely different deformation mechanism in comparison to systems with T_g above room temperature is invoked. A novel expression for the hardness of polymers in terms of crystallinity of the single components and/or phases, the T_g values, and the mass fraction of each component is proposed. This expression permits the calculation of (i) the room‐temperature H value of amorphous polymers, mainly containing single bonds in the main chain, provided T_g is known, and of (ii) the contribution of the soft liquidlike components (phases) to the hardness of the entire multiphase system. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1413–1419, 1999     

DSC study of melting and glass transition in gelatins

In the range from –50° to +130°C, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied cases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperatureT _g on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.

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Zusammenfassung Mittels DSC wurde im Bereich –50° bis +130°C die Temperaturabhängigkeit der Wärmekapazität für verschiedene Arten von Gelantine mit einem Wassergehalt von 2 bis 95% untersucht. Es wurde gezeigt, daß in allen untersuchten Fällen metastabile kollagenähnliche Strukturen in Gelen oder kristallinen Gelantinen gebildet werden, deren thermodynamische Parameter von den Bildungsbedingungen abhängen. Es wurden die charakteristischen Eigenschaften der Glasumwandlungen in amorphen Gelantinen und kristallinen Gelantinen mit unterschiedlichen Schmelzwärmen und einem unterschiedlichen Gehalt an geordneter Phase bestimmt. Spezielle Aufmerksamkeit wurde den strukturellen Eigenschaften von freiem und gebundenem Wasser gewidmet. Es wurde gezeigt, daß die Ab-hängigkeit der GlasumwandlungstemperaturT _g vom Gehalt an gebundenem Wasser generell für viele denaturierte Biopolymere anwendbar ist. Im Unterschied zu gebundenem Wasser fungiert freies Wasser in Gelatinen nicht als ein Weichmacher, bildet aber eine starre Matrix, die die Glasumwandlung verhindert.

     

“Order-disorder” transition model in aqueous solutions of aliphatic alcohols

A model of “order-disorder” type structural transitions in dilute aqueous solutions of lower aliphatic alcohols is proposed. Analytical expressions for the thermodynamic potential of the solution, its isobaric heat capacity increment, and the dependence of the temperature of a solution transition to a structurally ordered state on the alcohol concentration are obtained. A linear correlation between the concentration dependence of the heat capacity and the compressibility of the solution is proved to exist.     

Kinetics of thermoset cure and polymerization in the glass transition region

A theoretical approach to thermoset cure kinetics based on Arrhenius kinetics and mobility was developed by considering the activation of the reacting group and chain mobility as elementary steps for reaction. This extended kinetic equation was successfully applied to the curing of an epoxy by an amine, the trimerization of a cyanate, and to the polymerization of methyl methacrylate. Full agreement between theory and experimental data was obtained in all cases. The activation energies for chain mobility were exceptionally low (0.3–1 kJ/mol for bisphenol-A-based epoxy and cyanate) which indicates that the structural units must undergo only small-angle rotational oscillations to allow a reaction. A theoretical time–temperature–transformation (TTT) diagram is also presented. © 1993 John Wiley & Sons, Inc.     

On the correlation of the glass transition temperature of a copolymer with its comonomer sequences

The glass transition temperature of a copolymer depends not only on chemical composition but also on its comonomer sequences. This experimental fact is explained by Barton's and Johnston's equations. Their equations, though complicated, become simple, if a suitable parameter is used to describe the comonomer sequences. It is shown that with these new expressions, their equations can be used to understand glass transition temperatures of two additional types of copolymers, compatible multiblock copolymers and homopolymers with various tacticities treated as steric copolymers.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayWe wish to thank the reviewer for his/her kind linguistic improvement of this article.     

Comparison of calorimetric and IR-spectroscopic data for alcohols and alcoholic solutions

The heats of solution of alcohols in hexane can be considered as the energy necessary to break hydrogen bonds (H-bond). The amount of non H-bonded OH groups estimated from caloric data, are in good agreement with IR-spectroscopic data. Comparison of calorimetric and IR-spectroscopically determined H-bond energies permit the separation of intermolecular van der Waals effects from H-bond interactions. This separation shows that van der Waals interactions of alcohols or water should not be underestimated.     

The solubilization of alcohols in micellar solutions

The specific conductivities of dodecyldimethylbenzylammonium bromide (C12BBr) have been determined in aqueous butanol and aqueous benzyl alcohol solutions in the temperature range of 5-40°C. From these data the temperature dependent critical micelle concentration (cmc) was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The thermal properties such as standard Gibbs free energy, enthalpy and entropy of solubilization of alcohols in the micelles were estimated for the phase separation model. The change in heat capacity upon solubilization of alcohol in the micelle has been estimated form the above properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the PdCl2-catalyzed synthesis of allylic azides and allylic sulfonamides from homoallylic alcohols

According to experimental and literature data, the one-pot formation of allylic azides or sulfonamides from catalytic amounts of PdCl₂, homoallylic alcohols and TMSN₃ or TsNH₂ occurs through CC migration followed by regioselective nucleophilic addition on the Pd^II-activated CC bond and β-OH elimination.     

On the relaxation theory of glass transition in liquids

A method for calculating the constant in the main equation of glass transition (which relates the relxation time and the cooling rate near the glass transition temperature) with consideration given to the temperature dependence of the activation energy in this region is proposed. A modification of the main glass transition equation is considered. Application of this equation to the relaxation spectrometry of amorphous polymers and inorganic glasses is discussed.     

Nanofiller effect on the glass transition of a polyurethane

The effect of silicananofiller on the glass transition of a polyurethane was studied by DSC. Thepristine polymer exhibits a single glass transition at about –10°C.Uniform SiO2 spheres with different average sizes and narrow size distributionswere synthesized in solution by the Stöber method [1]. Both the effectsof silica content within the polymer and particle size were investigated,as well as two different surface treatments. Scanning electron microscopy(SEM) clearly confirms the presence of the particles within the polymer matrix,showing uniform distribution and no agglomeration. While shifting of the glasstransition has been reported by many authors, we have not seen any noticeableshift in this polymer. Surprisingly, we found no relevant effects when eitherincreasing the filler content or changing the particle size. Different amountsof particles with average diameters of 175, 395 and 730 nm did not affectthe glass transition temperature of the pristine polymer.     

Gas-chromatographic method of evaluation ofn-alkanol ability for self-association in pure liquid

The values of the gas-chromatographic indicator reflecting the capacity of analytes for self-association in pure liquids, δT _b.p., were estimated for C₁–C₉ and C₁₁ n-alkanols by capillary gas chromatography on a nonpolar stationary phase under isothermal conditions. The δT _b.p. values ofn-alkanols, found as the difference between the boiling points measured directly and those calculated from GC data, are correlated with thermodynamic characteristics of the formation ofn-alkanol associates in pure liquids. Usingn-alkanols as analytes with insignificant temperature increments of the retention indices, it was shown that the δT _b.p. values can be determined under conditions used in gas chromatography with temperature programming. In this way a single chromatographic run can be used to compare the capacities for self-association of analytes boiling over a wide temperature range. The C₂–C₉ n-alkanethiols, which are not associated in neat liquids, have negative δT _b.p. values. An interpretation of this finding is proposed. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 315–318 February, 2000.     

Thermochemical investigations of hydrogen-bonded solutions. Part 11. Expressions for predicting anthracene solubilities in alcohol+alkoxyalcohol mixtures based on mobile order theory

Experimental solubilities are reported for anthracene dissolved in eight binary mixtures containing 2-ethoxyethanol with 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 1-pentanol, 3-methyl-1-butanol and 1-octanol, and also in binary 1-pentanol+2-methoxyethanol and 2-methyl-1-propanol+2-propoxyethanol solvent systems at 25°C. Results of these measurements, combined with previously reported anthracene solubility data in 22 different alcohol +2-alkoxyethanol (2-methoxyethanol, 2-propoxyethanol and 2-butoxyethanol) solvent mixtures, are used to test the limitations and applications of expressions derived from Mobile Order theory. The first predictive expression assumes only formation of homogeneous self-associated hydrogen-bonded species, whereas the second equation includes additional terms to account for heterogeneous complex formation between the dissolved alcohol and 2-alkoxyethanol solvent molecules. Both equations predict the observed anthracene solubilities to within an average absolute deviation of about 3%.