The Use of Inverse Gas Chromatography (IGC) to Determine the Surface Energy of RDX

The surface properties of RDX play an important role in enhancing mechanics performances of the propellants and explosives. In this work, thereby, inverse gas chromatography (IGC) using various probe liquids as the medium was used to determine the surface energy components of RDX containing both dispersive and polar components, which were acquired respectively from neutral probe liquids (such as n‐hexane, n‐heptane, n‐octane) and polar probe liquids (such as chloroform, benzene, methanol). The results show that RDX located in different column temperatures has difference in the surface energy and possesses more surface energy when there is high temperature. The calculated formula of the total surface energy with temperature is: , and it is also found that dispersive, polar, electron acceptor, and electron donor components of RDX are , , , and , respectively. These results demonstrate that the dispersive component is the primary part of the total surface energy, and RDX has an acid performance.     

Surface energy mapping of Kevlar® fibers by inverse gas chromatography

The surface energy characteristics of three Kevlar® fibers have been systematically studied using two inverse gas chromatography (IGC) techniques, i.e., at an infinite probe dilution and at a finite probe concentration, with the latter allowing a unique mapping of the surface energy levels, which complements greatly the more traditional characterization of the highest energy sites. The standard thermodynamic parameters, such as the free energy −Δ , and the adsorption enthalpy and entropy (Δ and −Δ ), as well as the dispersive and the specific component ( and ΔG^sp/I^sp) of the fiber surface energy, were determined from the retention behavior at zero coverage of selected molecules of various polarity. The values are between 49–58 mJ m⁻² for the three fibers at 50°C. The polar components, ΔG^sp or I^sp, calculated by three different methods, reveal the polar feature of the fiber surface. It is interesting to note that the adsorption enthalpies Δ for the short chain alkane probes are nearly the same as their liquefaction energies. Using the second IGC approach, i.e., at finite concentration, the isotherms for the adsorption of n-octane and n-hexylamine on the three selected Kevlar® fibers were constructed by the one-peak method. These are shown to be instrumental to establish the corresponding energy distribution functions. The results may indicate that, unlike the alkane probes, the polar molecules interact strongly with the Kevlar® fiber surfaces, which appear, in this case, energetically heterogeneous. The resulting energy distribution mapping opens new avenues towards the surface characterization of the global surface without the restriction of the averaging imposed by other bulk analysis techniques. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 487–500, 1998     

Kinetics of ion exchange in monodisperse resin

Ion-exchange kinetics within a conventional strong base resin, Dowexl-8X®, and a resin with uniform particle size, Dowex® Monosphere® Tough Gel® TG550A®, were investigated using neutron activation analysis and radio-tracer techniques. The kinetics of ion exchange were measured in a batch and in a “shallow-bed” flow system. The experimental data were compared with the results of model computations. The diffusivities of several anions within TG550A and Dowexl-8X were deduced. It was found that at 25°C Br^-, Cl^-, OH^-, and Na⁺ diffuse within TG550A with the diffusion coefficients = 6.0 × 10^-7 cm²/s, = 1.2 × 10^-6 cm²/s, = 7.0 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. Diffusion of anions within a conventional resin, Dowexl®, was slower: = 3.5 × 10^-7 cm²/s, = 6 × 10^-7 cm²/s, = 2.7 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. A higher rate of ion diffusion and the bead-size uniformity may make monodisperse Dowex Monosphere Tough Gel TG550A resin attractive for analytical applications. The difference in properties between conventional and monodisperse resins is not sufficient to affect the large volume applications of resins. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1271–1283, 1997     

Effect of magnetic field on discotic nematic liquid crystalline polymers under simple shear flow

The effect of magnetic field on the discotic nematic liquid crystalline polymers (LCPs) is analyzed with the extended Doi theory, in which the molecular shape parameter (β) is defined at ?1.0. The evolution equation for the probability function of the discotic nematic LCP molecules is solved without any closure approximations. The transition among flow‐orientation modes, such as tumbling, wagging, and aligning defined similar to the rodlike LCPs, is strongly affected by the magnetic fields. The new aligning flow‐orientation mode observed for the rodlike LCPs under magnetic fields also can be investigated in the lower shear rate region. On the other hand, the effect of magnetic fields parallel to the x‐ and y‐axis on the time‐averaged first and second normal stress differences ( , ) are also studied. It can be seen that the shear rate regions of the sign changes of , are completely contrary to those conclusions achieved for the rodlike LCPs. In addition, the absolute values of increase with the magnetic field strength in the lower shear rate range owing to the new aligning flow‐orientation mode. Finally, the flow‐phase diagram versus β is also discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

The kinetics and mechanism of the chloride-chlorate reaction

The kinetics of the reaction have been studied at 25°C. in strong acid solution; the effects of acidity, chloride, chlorate and chlorine are reported. A mechanism is postulated to interpret the peculiar features of this reaction as well as the stoichiometry and some of the kinetics of the parallel reaction The mechanism involves HClO₂ and HOCl as intermediates General rate expressions are derived for the formation of chlorine dioxide and chlorine, and the individual rate constants are calculated. An expression is obtained for the relationship between the ratio of chlorine dioxide to chlorine produced and the ratio of chlorate to chloride.     

Evaluation of the termination mode in the radical polymerization of 2,2,2‐trifluoroethyl α‐fluoroacrylate

The mode of termination of 2,2,2‐trifluoroethyl α‐fluoroacrylate (FATRIFE) in radical polymerization was studied, and only termination by recombination occurred, which led to telechelic macromolecular structures. The radical polymerization in acetonitrile was carried out to synthesize oligomers with a low number average degree of polymerization ( )_cum (about 20), using tert‐butylcyclohexyl peroxydicarbonate (TBCPC) as initiator at 75 °C. The initial [TBCPC]₀/[FATRIFE]₀ molar ratio was monitored to evaluate its influence on the ( )_cum of α‐fluoroacrylic oligomers. The ¹H NMR analysis of the polymers showed that the ( )_cum values obtained were higher than 40, in spite of a high C₀ value. To explain these results, the mode of termination was evaluated using the following kinetic law: . The development of kinetic relationships allowed us to calculate the ratio k_prt/k_i·k_p as about 17–30 mol s l^?1, and to confirm that primary radical termination (PRT) was in competition with bimolecular macromolecular termination (BMT). © 2002 Society of Chemical Industry     

A corresponding states treatment of saturated density,surface tension and capillary constant of cryogenic liquids and refrigerants

Using a new set of energy (kT) and length (σ) parameters, a corresponding states treatment is applied to the calculation of some thermophysical properties in a generalised non-dimensional form. The saturated density is well represented by the following equation: for all the liquids studied here. The surface tension correlations are $ \gamma _r^* = 2.055\left({1.219 - T_r^*} \right)^{1.240} $ for cryogenic fluids and hydrocarbons and $ \gamma _r^* = 2.322\left({1.228 - T_r^* } \right)^{1.244}$ for refrigerants. An interpretation of the index in the density equation and the constants in the surface tension equations is given. Using these correlations, an equation is also proposed for the capillary constant.     

Elongational flow studies of hinged rodlike molecules

Poly(amino acid) in an intermediate state of its helix-coil transition is known to be in a hinged rodlike conformation. In this work, the responses of poly(amino acids) in the hinged rodlike conformation against an elongational flow field were investigated by monitoring their flow-induced birefringence. Poly(L-glutamic acids) (PGA) and poly(γ-benzyl-L-glutamate) (PBLG) were examined as polyelectrolyte and noncharged poly(amino acids), respectively, and the results were compared. In the plots of flow-induced birefringence, Δn, against strain rate, $ {\dot \varepsilon } $, for hinged rodlike PBLG, there was a critical strain rate, $ \dot \varepsilon_0 $, below which Δn was not observed. Over $ \dot \varepsilon_0 $, the birefringence pattern observed was identical with that of rodlike molecules. The Δn vs. $ {\dot \varepsilon } $ plot for hinged rodlike PGA had characteristics of a rigid rod at any strain rate and there was no $ \dot \varepsilon_0$ observed. The rotational diffusion coefficient, D_r, of PBLG in the hinged rodlike conformation was larger than that for its helical conformation, while D_r, for the hinged-rodlike PGA was smaller than that for its helical conformation. It is concluded that the hinged-rodlike PGA molecule is in an extended form and that the hinged-rodlike PBLG is hydrodynamically more compact and rigid than that in its quiescent state. It is deduced that at $\dot \varepsilon_0$ hinged rodlike PBLG molecules collapse to a conformation optically anisotropic and mechanically rigid. © 1996 John Wiley & Sons, Inc.     

Polymer melt elongation—methods,results, and recent developments

For film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ ? \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂ ≥ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₃₃, the ratio m = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂/\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation-induced anisotropy of the rheological behavior.     

Shear rate dependence of the viscosity of cellulose nitrate solutions in the dilute concentration regime revisited

A detailed rheological study of cellulose nitrate in ethylacetate had been carried out in the dilute concentration (c) regime, covering a degree of polymerization (DP) range between 300 < DP_η < 7000 and shear rates ($ \dot \gamma $) between 100 s^?1 < $ \dot \gamma $ < 2000 s^?1. The results show a strong dependence of the transition Newtonian to non-Newtonian behavior on the three variables $ \dot \gamma $, DP, and c, similar to that found recently on solutions of synthetic polymers. Emphasis has been put on the critical concentrations corresponding to the standard shear rate 1000 s^?1 to correspond to the standard conditions ($ \dot \gamma $ ? 1000 s^?1; 0.3 < [η] · c < 0.6; DS = 2.90 ± 0.02) proposed for the determination of the intrinsic viscosity [η] of cellulose nitrates. It is shown that solutions with concentrations adjusted according to the above given conditions still exhibit Newtonian behavior, up to the highest range of DP. It follows, therefore, that applying the standard conditions, an extrapolation to $ \dot \gamma $ = 0 as has been proposed often for the intrinsic viscosity determination of cellulose nitrate is not advisable and results in considerable error. Considering the relationship between [η] and DP, the present results indicate that the decrease of the exponent ( a ) from a = 1.0 to a = 0.76, taking place above a DP ? 1000, is not a consequence of the applied shear rate but rather of the molecular properties of the solutes themselves.     

Limitations of the Zero‐Length Column Technique to Measure Diffusional Time Constants in Microporous Adsorbents

The zero‐length column (ZLC) technique has been developed to measure the intracrystalline diffusivity of strongly adsorbed species in large zeolite crystals above 50 μm in the Henry's law range of sorption equilibrium. The ZLC is a macroscopic technique, and there is a need of large crystallites or pellets to measure the intracrystalline diffusivity D_c of fast diffusion species or the macropore diffusivity D_P of weakly adsorbed species, respectively. Another limitation is that ZLC desorption curves produce similar concentration profiles (linear isotherms) in bidisperse adsorbents (pellets) under macropore or micropore diffusion control. Moreover, the forms of the response curves are very similar in both diffusion‐ and nonlinear equilibrium‐controlled processes, leading to some misinterpretations of ZLC experiments. In this work, two criteria are developed showing that, in order to macroscopically measure the micropore diffusion time constant  or the macropore diffusion time constant , the time of the ZLC experiments t should be higher than 7.0 × 10^?2 or 7.0 × 10^?2 , respectively. The interpretation of the ZLC response curve data is also checked in two completely different regimes, showing that a single ZLC response curve is not enough to conclude if a system is under a kinetic or an equilibrium regime.     

Polypentadecalactone prepared by lipase catalysis: crystallization kinetics and morphology

BACKGROUND: This work addresses the need to better understand the crystallization kinetics and morphology of poly (ω‐pentadecalactone) (PPDL). This polyester has promising mechanical properties and a unique structure that resembles that of polyethylene. PPDL is a member of the poly(ω‐hydroxy fatty acid) family, which can be derived from biobased feedstocks. RESULTS: PPDL (M_n = 34 000 g mol^?1 and dispersity D = M_w/M_n = 2.7) was synthesized using enzyme catalysis. Equilibrium melting enthalpy and equilibrium melting point were determined using extrapolation techniques, being 227 J g^?1 and 101 °C, respectively. In addition, the equilibrium melting point ( ) was found to be 109.3 °C by the nonlinear Hoffman‐Weeks plot. For , the lateral surface free energy (σ), fold surface free energy (σ_e) and fold work (q) are 10.4 erg cm^?2, 47.5 erg cm^?2 and 2.6 kcal mol^?1, respectively; while for , they are 25.1 erg cm^?2, 46.6 erg cm^?2 and 2.6 kcal mol^?1, respectively. The results indicated the existence of a regime I to regime II transition during crystallization at about 80 °C. Polarized optical microscopy and AFM provided further evidence for the regime I–II transition. In regime I, coarse spherulites were formed through splaying out and occasional branching of lamellae, as well as stacking of lamellae through screw dislocation. In contrast, in regime II, banded spherulites were formed through crystal twisting. CONCLUSION: Morphological changes in PPDL at spherulitic and lamellar levels in regimes I and II were confirmed by differential scanning calorimetry, POM and AFM. Copyright © 2009 Society of Chemical Industry     

Kinetic and thermodynamic investigation of Arthrospira (Spirulina) platensis fed‐batch cultivation in a tubular photobioreactor using urea as nitrogen source

BACKGROUND: Fed‐batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires a knowledge of the kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow‐rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: The optimal values obtained were T = 32 °C and U = 1.16 mmol L^?1 d^?1, under which the maximum cell concentration was 4186 ± 39 mg L^?1, cell productivity 541 ± 5 mg L^?1 d^?1 and yield of biomass on nitrogen 14.3 ± 0.1 mg mg^?1. Applying an Arrhenius‐type approach, the thermodynamic parameters of growth (ΔH* = 98.2 kJ mol^?1; ΔS* = ? 0.020 kJ mol^?1 K^?1; ΔG* = 104.1 kJ mol^?1) and its thermal inactivation ( kJ mol^?1; kJ mol^?1 K^?1; kJ mol^?1) were estimated. CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts. Copyright © 2012 Society of Chemical Industry     

Thermochemistry and Thermodynamics of Trinitrophloroglucinol Dissolved in DMF and EtOH at 298.15 K

The enthalpies of solution of 2,4,6‐trinitro‐1,3,5‐trihydroxybenzene (trinitrophloroglucinol, TNPG) in N, N‐dimethylformamide (DMF) and EtOH are determined. The thermodynamics of these processes are also studied. The experiments are carried out by a SETARAM C80 calorimeter at 298.15 K. The empirical formulas for enthalpies of solution of TNPG in both DMF and EtOH are calculated by polynomial expressions. The resulting formulas are: (in DMF), and (in EtOH).     

Characterization of polyvinyl chloride part II. The unperturbed end to end distance values obtained from a new GPC method and viscometry

A new gel permeation chromatography (GPC) method is proposed for determining the unperturbed end-to-end distance, \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{r_0 ^2 }}{M}} \right)^{0.5} $\end{document}, of polymers of known molecular weights, Mn and Mw. This method requires the value of \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{r_0 ^2 }}{M}} \right)^{0.5} _{{\rm ps}} $\end{document} of polystyrene which was determined through viscometry to be 0.735 \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{{\rm {\AA}}^2-{\rm mole}}}{{gm}}} \right)^{0.5} $\end{document} Polyvinyl chloride (PVC) was chosen to illustrate the method and \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{r_0 ^2}}{M}} \right)^{0.5} _{pvc} $\end{document} was found to be 0.99 from GPC data which is in agreement with the result obtained from viscometry, \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{r_0 ^2}}{M}} \right)^{0.5} _{pvc} $\end{document} = 1.01. All \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{r_0 ^2 }}{M}} \right)^{0.5} $\end{document} values were determined at 30°C. The advantage to this method lies in its speed and economy of materials.     

Viscosity of bead suspensions in polymeric solutions

Viscosity measurements made by a cone-plate viscometer on polyisobutylene in decalin solutions at different concentrations and their corresponding glass bead suspensions with filler loadings up to 40% by volume are reported. The range of shear rate $ \dot \gamma $ investigated is between 0.1 and 1000 sec^?1. The solutions show shear-thinning behavior, and the relative viscosity η_r of the slurries generally decreases with increasing shear rate. The results indicate two different types of mechanism, respectively at high and low shear rates. At low $ \dot \gamma $, the relative viscosity can be correlated extending relations already well known for suspensions in Newtonian liquids which are based on the mechanism of aggregate disruption. The behavior at high $ \dot \gamma $ values is believed to be due to the influence of the filler on the flow properties of macromolecules, in particular on relaxation time. Through a shifting procedure, an increase in relaxation time which depends on filler content and not on polymer concentration is shown.     

Empirical correlation of flow properties of poly(vinyl chloride)

Empirical correlations of flow properties of poly(vinyl chloride) were made using data reported by a number of investigators. Correlation was made by plotting the reduced variable viscosity η/η₀ versus \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w )/(_\rho RT) $\end{document} or \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w ^{0.5} )/(_\rho RT) $\end{document} for unplasticized PVC and versus \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w ^{0.5} )/(_\rho RTW_2 ^a ) $\end{document} with polymer concentration, W₂, for PVC containing plasticizer.     

Dye binary mixture formulation by means of derivative ratio spectra of the Kubelka–Munk function

In this study, a new method is introduced for the determination of dye concentration in fabrics dyed with bicomponent dye mixtures. The reflectance spectra of the samples dyed with different binary mixtures of dyes were recorded between 400 and 700 nm. The obtained spectra were divided by a standard spectrum of each of the components in the mixtures and the derivative spectra were calculated. The amounts of dyes were determined by measurements in suitably selected wavelengths in the acquired derivative ratio spectra. The obtained results indicate that the developed derivative ratio spectra method is more accurate than the normal Kubelka–Munk method. The proposed derivative method is simple, accurate, and suitable for quantitative analysis of samples dyed with binary mixed shades. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Preparation and Performance of Highly Efficient Au Nanoparticles Electrocatalyst for the Direct Borohydride Fuel Cell

Au nanoparticles supported on Vulcan XC‐72R carbon were prepared by a modified NaBH₄ method in aqueous solution and employed as electrocatalyst of oxidation for the direct borohydride fuel cell (DBFC). The morphology and structure of as‐prepared particles were examined by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). It was found that Au nanoparticles were mainly about 3.0 ± 0.5 nm in size and uniformly distributed on the surface of Vulcan XC‐72R carbon. The electrooxidation behaviors of and fuel cell performances using carbon‐supported Au nanoparticles as catalysts were investigated. Compared with Au/C prepared by conventional reduction method, the kinetics of oxidation on as‐prepared carbon supported 3.0 ± 0.5 nm Au nanoparticles were significantly improved. The DBFC employing carbon supported 3.0 ± 0.5 nm Au nanoparticles showed a maximum power density of 85.3 mW cm^–2 at 60 °C.