A triarylboron-based fluorescent thermometer: sensitive over a wide temperature range

Feeling blue: the luminescence of a triarylboron compound has a high quantum yield (at least 0.64) over a wide temperature range (-50 to +100 °C) and changes from green to blue as the temperature is increased. The luminescence color was determined by the population of the two distinct excited-state conformations-a local excited state (high temperature) and a twisted intramolecular charge-transfer state (low temperature).     

Stable superhydrophobic polybenzoxazine surfaces over a wide pH range

In this study, we report on a simple two-step casting process designed to create a stable superhydrophobic surface. This method possesses the advantages of being both simple and inexpensive as well as utilizing non-fluorine-containing compounds. Most interestingly, we found that the as-prepared surface possesses superhydrophobic properties not only for pure water but also for corrosive water under both acidic and basic conditions. Furthermore, the superhydrophobic polybenzoxazine surfaces had excellent environmental stability with regard to both heating and organic solvent treatment in terms of the contact angle to water.     

Adsorption dynamics over a wide range of breakthrough concentrations

Conclusions A simple method is proposed for carrying out analytical calculations on adsorption dynamics; by its use one can make allowance for longitudinal effects in determining coefficients of external mass transfer and internal diffusion, and dynamic bed activities.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 56–62, January, 1981.     

Bacterial attachment over a wide range of ionic strengths

The number of bacterial cells adhered on a glass surface was counted over a wide range of ionic strengths. The counted number increased linearly with the square root of time. The rate of attachment increased with the increase in ionic strength and then plateaued. The rate of attachment was analyzed on the basis of the potential barrier between the surface of the bacterial cell and that of the substratum. An equation for formulating the dependence of the attachment rate on the ionic strength was proposed, which seems to be useful for the systematic understanding of bacterial attachment in various environments, from terrestrial to marine.     

Mimicking the lotus effect: influence of double roughness structures and slender pillars

Surface roughness is known to amplify hydrophobicity. The apparent contact angle of a drop on a rough surface is often modeled using either Wenzel's or Cassie's formulas. These formulas, along with an appropriate energy analysis, are critical in designing superhydrophobic substrates for applications in microscale devices. In this paper we propose that double (or multiple) roughness structures or slender pillars are appropriate surface geometries to develop "self-cleaning" surfaces. The key motivation behind the double structured roughness is to mimic the microstructure of superhydrophobic leaves (such as lotus). Theoretical analysis similar to that presented in the paper can be used to obtain optimal geometric parameters for the rough surface. The calculation procedure should result in surface geometries with excellent water repellent properties.     

The dynamic properties of plasticized epoxies over a wide frequency range

Summary The dynamic mechanical properties of a class of plasticized epoxies were investigated over a wide temperature range by means of a Rheovibron Viscoelastometer. Master curves for storage and loss moduli were produced by means of the frequency-temperature superposition principle, as well as for relaxation modulus by a conversion formula. The effect of plasticizer percentage on the said parameters, as well as the loss peaks, corresponding to and relaxations was investigated.     

The H+NO recombination reaction over a wide temperature range

Rate coefficients of the title reaction have been measured in a high‐temperature photochemistry (HTP) reactor using Ar as the bath gas. H atoms were generated by flash photolysis of NH₃ and their relative concentrations were monitored by resonance fluorescence. The data are best fitted by k(295–905 K) = 6.5 × 10^?34 (T/K)^0.206 exp(780K T) cm⁶ molecule^?2 s^?1, with ±2σ precision values varying from 16 to 36% and corresponding suggested accuracy levels of 29–42%. Using a literature value for the relative collision efficiencies of N₂ and Ar indicates that for N₂ as the third body the above rate coefficient expression should be multiplied by 1.6. This leads to good agreement with two recent near 1000 K measurements. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 374–380, 2003     

Rate of the retro-Diels-Alder dissociation of 1,2,3,6-tetrahydropyridine over a wide temperature range

Rate constants for the retro-Diels-Alder dissociation of 1,2,3,6-tetrahydropyridine, to 1,3-butadiene and methanimine, have been measured over 650–1450 K. To cover this range, three separate techniques were used at three laboratories: laser schlieren and single pulse shock tube methods, and a comparative rate flow system technique. The derived rate constants are extrapolated to the high-pressure limit with an RRKM model parameterized to fit the falloff observed in the laser-schlieren measurements. The resulting high-pressure rate constants show a reduction in activation energy of about 10 kcal/mol, comparing the isoelectronic cyclohexene, but little change in A-factor. There is an apparent increase in activation energy of 4 kcal/mol over the temperature range of these experiments, which is just outside probable error. Such a rise in activation energy is in marked contrast to the drop usually seen in simple bond fission, and may reflect a change from a concerted to a stepwise, biradical mechanism at high temperatures.     

Effect of size in oxygen electroreduction on gold over a wide range of pH

The electroreduction of molecular oxygen on polycrystalline gold and 20Au/C nanoparticles synthesized on XC72R soot is studied over a wide range of pH. Changes in the character of the polarization curves and a considerable increase in half-wave potential (～100 mV) upon transitioning from a compact to a nanodisperse metal were established. A triple increase in the exchange currents is observed for nanoparticles relative to polycrystalline gold. It is suggested that the enhancement of the catalytic activity of a nanodisperse metal is a result of changes in the electronic structure of the d-sublevel of surface atoms.     

Imines that react with phenols in water over a wide pH range

Cyclic imine derivatives that react with phenols, including tyrosine residues of peptides, have been developed. Reactions of the imines with phenols proceeded in water over a wide pH range (pH 2-10) at room temperature to 37 degrees C and afforded Mannich products without the need of additional catalysts.     

Determination of nitrogen diffusivities in liquid cyclohexane over a wide temperature range

The diffusivity of nitrogen in liquid cyclohexane has been measured at temperatures from 21 °C to 140 °C and at pressures of 10 – 15 atm, using a high pressure wetted sphere absorber apparatus. The diffusivity increased from 4.0 × 10⁻⁵ cm² s⁻¹ to 2.8 × 10⁻⁴ cm² s⁻¹ over this temperature range.Rippling of the film at the higher flow rates restricted the flow rate range which could be utilized for the diffusivity determinations. The measured absorption rates for flows in which rippling occurred were up to 15% higher on a 20 mm sphere and up to 40% higher on a 30 mm sphere. This limited the suitability of the wetted sphere absorber for this type of work.     

Novel anisotropic supramolecular hydrogel with high stability over a wide pH range

The hydrolysis of the carboxylic ester bond, by a base or catalyzed by an enzyme under weak basic conditions, serves as the only path to obtain a novel anisotropic supramolecular hydrogel that is stable over a wide pH range. This result not only expands the molecular scope of supramolecular hydrogelators but also illustrates the design principles for creating pH-stable supramolecular soft materials.     

Additive estimates of the thermodynamic properties of triene hydrocarbons over a wide temperature range

An increment method for calculating the thermodynamic properties of aliphatic triene hydrocarbons is suggested. The method is based on substituting procedures and additive inclusion of 1,4-and 1,5-carbon-carbon intramolecular interactions. Parameter values for estimating the enthalpies of formation of gaseous alkatrienes at 298.15 K were found. A procedure for determining the thermodynamic properties of conjugated alkatrienes at arbitrary temperatures was developed. This procedure is based on the additive determination of the coefficients of polynomials that describe the temperature dependences of properties. The parameters for determining the isobaric heat capacities, entropies, and reduced enthalpies and Gibbs energies of conjugated triene hydrocarbons in the gas phase were found. Calculations reproduce experimental data with accuracy at the level of measurement errors. A thermodynamic analysis of the rearrangements of 2,6-dimethyloctatrienes (alloocimene isomers) was performed. The compositions of equilibrium mixtures of 14 aliphatic terpenes were determined at five gas phase temperatures from 298.15 to 1000 K.     

Adsorption isotherms and kinetic characteristics of methane on block anthracite over a wide pressure range

It is important to quantitatively understand the methane adsorption and transport mechanism in coal for an evaluation of the reserves and for its production forecast. In this work, a block coal sample was chosen to perform the CH4 adsorption experiments using the gravimetric method at temperatures of 293.60 K, 311.26 K, 332.98 K and 352.55 K and pressures up to 19 MPa. The excess adsorption capacity of CH4 in dry block anthracite increased, followed by a sequence decrease with the increasing pressure. High temperature restrained the growth of the excess adsorption due to that the adsorption is an intrinsically physical and exothermic process. The excess adsorption peak decreased slowly with the increase of temperature and intersected at a pressure of more than 18 MPa; meanwhile, the pressure at the excess adsorption peak increased.The existing correlations were examined in terms of density rather than pressure. The DR+k correlation, with an average relative deviation of ±0.51%, fitted our data better than the others, with an average relative deviation of up to 2.29%. The transportation characteristics of CH4 adsorption was also investigated in this study, including the adsorption rate and diffusion in block coal. The kinetic data could be described by a modified unipore model. The adsorption rates were found to exhibit dependence on pressure and temperature at low pressures, while the calculated diffusivities exhibited little temperature dependence. In addition, the kinetic characteristics were compared between CH4 and CO2 adsorption on the block coal. The excess adsorption ratios of CO2 to CH4obtained from the DR+k model decreased with the increasing pressure.     

Crystallization-induced gelation of ethylene/1-butene copolymers over a wide crystallinity range

The crystallization-induced gelation from decalin solutions of a series of ethylene-butene random copolymers covering the range of crystal weight fraction 0.32–0.74 and having nearly equal molar weights has been investigated as a function of concentration. Swollen as well as dried gels have been characterized by means of differential scanning calorimetry, mechanical tests and scanning electron microscopy. The critical concentration for gelation is shown to be strongly dependent on the crystallinity of the polymers. On the contrary, the critical concentration for chain entanglement is quite invariant. A liquid-liquid phase separation phenomenon prior to the crystallization upon cooling is disclosed for the more crystalline materials. The better solubility of the co-unit rich copolymers is ascribed to a more favorable interaction parameter towards decalin with increasing co-unit content. Common aspects of the gelation process of the copolymers with that of atactic amorphous and isotactic semicrystalline polystyrene are discussed.     

Dielectric constants of fluid mixtures over a wide range of temperature and density

A new expression is presented for estimating the dielectric constant of a fluid mixture as a function of temperature, density and composition. The estimated dielectric constants (and their derivatives) are required for phase-equilibrium calculations, based on an equation of state, for systems containing electrolytes and nonelectrolytes. The new expression holds for the entire range of fluid densities, from zero to liquid-like densities. Mixing of components is performed on a volume-fraction basis at constant temperature and constant reduced density. For polar components where data are not available at the temperature and/or reduced density of interest, the well-characterized behavior of water is used to extrapolate the available pure-component data. The importance of using the correct density of the mixture is shown. Using one adjustable parameter for each nonideal binary subsystem, predicted results can be significantly improved.     

The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C₅H₈O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900–1500 K, 110–560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663–773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉_down is a fixed 400 cm^?1. Arrhenius expressions for k_∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.