Shrinking rate of conducting grains in HCl–protonated polyaniline,polypyrrole, and polypyrrole/polyaniline blends with their thermal aging

The dc electrical conductivity (σ) of HCl‐protonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under room atmosphere. The change of σ with the temperature (T) and the decrease of σ with the thermal aging time (t) are consistent with a granular metal type structure, in which conductive grains are randomly distributed into an insulating matrix. Aging makes the grains shrink in a corrosion‐like process. From σ = σ(T) measurements the ratio s/d, where s is the average separation between the grains and d their diameter, as well as the rate d(s/d)/dt of their decrease with t were calculated. These revealed that the conductive grains consist of a shell, in which aging proceeds at a decreasing rate, and a central core, which is consumed at a much slower rate. Our measurements not only permitted the estimation of the shell thickness, which lies between 0 and 5 Å, but also gave quantitative information about the quality of the shells and the cores from their aging rates. The shells are consumed with an average rate of d(s/d)/dt = 6.6 × 10^?4 (h^?1), which is about 5 times greater than the more durable cores. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 117–122, 2005     

Anionic difunctionalization with 1,1-bis(4-t-butyldimethylsiloxyphenyl) ethylene. Synthesis of ω,ω-bis(phenol)-functionalized polystyrene condensation macromonomers

ω,ω-Diphenolpolystyrenes (6) can be synthesized in quantitative yields by reacting poly(styryl)lithium with 1,1-bis(4-t-butyldimethylsiloxyphenyl)ethylene (1), followed by methanol termination and hydrolysis with dilute acid. The initially formed 1,1-bis(4-t-butyldimethylsiloxyphenyl)alkyllithium can be reacted with additional styrene monomer to form a polystyrene internally substituted with two in-chain phenol groups after methanol termination and acid hydrolysis. The diphenol-substituted polystyrene condensation macromonomers have been characterized by end-group titration, size exclusion chromatography, thin-layer chromatography, and ultraviolet-visible, ¹H and ¹³C NMR spectroscopy. Chain-extension reactions of 6 (M_n = 2.6 × 10³g mol^?1) with bis(trichloromethyl)carbonate produced the corresponding comb-type, branched polymer with estimated Mⁿ(SEC, polystyrene standards) = 1.2 × 10⁴g mol^?1 and no detectable residual condensation macromonomer. The second order rate constants for the addition reaction of excess poly(styryl)lithium with 1 and with 1-(4-t-butyldimethylsiloxy-phenyl)-1-phenylethylene (3) have been estimated to be 1.7 × 10^?3M^?1/2S^?1 and 3.2 × 10^?3M^?1/2S^?1 respectively. A sigma value (σ) of ?0.46 has been estimated for the t-butyldimethylsiloxy substituent.     

Rubber elasticity on chemical relaxation

The applicability of the formula f(t) = n(t)RT(α ? α^?2) suggested by Tobolsky as the basis of chemorheology has been discussed. In this expression, f(t) is the stress after t hours, n(t) is the crosslinking density (mole/cc) after t hours, R is the gas constant, T is the absolute temperature, and α is the extension ratio. We have discussed the applicability of this formula, in another words, whether the degraded stress f(t) calculated from this formula would be consistent with the initial stress f_t(0) of other polymer if the degraded crosslinking density values n(t) are equal to those of n_t(0), the initial density values n(0) of other polymer. Natural rubber vulcanizates and SBR vulcanizates were used as samples in these experiments. Assuming n(t) = σ(t) n(0), α(t′) = 1, the applicability of the above formula was recognized from our experimental results.     

On the spectral density of a class of chaotic time series

The purpose of this paper is to show explicitly the spectral density function of the stationary stochastic process determined by a certain class of two-dimensional maps F_α defined below (α is a parameter in (0, 1)), the random variable φ(x, y) = x and the invariant probability described below. We first define the transformation T_α: [0, 1]←[0, 1] given by T _α(x) = {x/α if 0 ≤x < α and (α(x?α)/1 ?α) if α≤x≤ 1 where α∈ (0, 1) is a constant. The map T_α describes a model for a particle (or the probability of a certain kind of element in a given population) that moves around, in discrete time, in the interval [0, 1]. The results presented here can be stated either for T_α or for F_α but we prefer the latter. The results for T_α can be obtained from the more general setting described by F_α. The map F_α is defined from K = ([0, 1]× (0, α)) ∨ ([0, α]×[α, 1]) ?;R;² to itself and is given by F_α(x, y) = (T_α(x), G_α(x, y)) for (x, y) ∈K, where G _α(x, y) = {αy if 0 ≤x < α and α + ((1 ?α)/α)y if α≤x < 1. The spectral density function of the stationary process with probability ν (invariant for F_α and absolutely continuous with respect to the Lebesgue measure) Z_t = X_t + ξ_t = φ{F^t_α(X₀, Y₀)} + ξ_t for t∈Z where (X₀, Y₀) ∈R² and ξ_t}_t∈Z is a white noise process, is given explicitly (Theorem 1) by f _Z (λ) = f_X(λ) + (σ²_ξ/2π) = (1/2πvar(X_t))[γ{exp(iλ)}?C(0)] + (σ²/2π) for all λ∈[0, 2π), where var(X_t) = (α²?α + 1)(α²? 5α + 5){12(2 ?α)²}^?1, γ is given by Equation (2.10) of Proposition 5 and C(0) = (1 + α²?α³){3(2 ?α)}^?1. We also estimate the parameter α based on a time series.     

Collisional Probing of the Transition-State Structure of a Bimolecular Reaction

The total cross section σ_B(E) for the Ca(¹D) + HBr → CaBr(B²Σ⁺) + H reaction as a function of collision energy has been measured using crossed atomic and molecular beams. The maxima exhibited by σ_B(E) with increasing energy are attributed to the opening of successive bending vibrational reaction channels that proceed via a [Ca(¹D) ⃛ Br ⃛ H]^‡ transition state. A dynamical model for the reaction may be constructed in terms of Landau-Zener probabilities for curve crossing at two locations on the reaction path, coupled with a preference for consumption of transition-state vibrational energy.     

Characterization of the aging behavior of raw epoxidized natural rubber with a rubber processing analyzer

Tests of the strain sweep, frequency sweep, and stress relaxation for raw epoxidized natural rubber were carried out with a rubber processing analyzer. The results showed that the complex viscosity, η*, decreased with the prolongation of the aging time in the region of Newtonian flow, but in the region of non‐Newtonian flow, the decrement of η* with a rising shear rate decreased with the prolongation of the aging time. The torque (S′) response from the strain sweep indicated that aging brought about an obvious decrease in the increment of S′ with rising strain in the linear viscoelastic region and a small increase in the slope of the plateau on the curve of the S′ response in the nonlinear viscoelastic region. The stress relaxation rate constants k and b, calculated according to the equations S_t = S₀e^?kt and S_t = S₁t^?b (where S_t, S₀, and S₁ are the stresses at relaxation time t, t = 0, and t = 1, respectively), increased, and the stress relaxation time obtained directly from the rubber processing analyzer shortened with the prolongation of the aging time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1277–1281, 2006     

The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures

Softness parameters σ_M for cations and σ_X for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σ_M = [σ_A (M^m+) - σ_A(H⁺)]/σ_A(H⁺) and σ_X = [σ_B(X^a?) - σ_B(OH^?)]/σ_A(H⁺) where σ_A = [σI_i(M) + ΔH⁰_h(M^m+)]/m and σ_B = [-E_a(X) + ΔH⁰_h(X^a?)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H⁺ and OH^?) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four-coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one-coefficient equation involving the softness parameters is proposed to deal with next-nearest-neighbor interactions in binary common-ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni-univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.     

Isothermal rupture characteristics of a plasticized poly(vinyl chloride) in the glass–rubber transition zone

Constant strain-rate uniaxial extension tests to rupture were performed at 23°C on a plasticized poly(vinyl chloride) (PVC) in the glass-to-rubber transition zone, T_g = ?18°C, where experimental failure time t_f is equal to or greater than material relaxation time τ. Range of strain rate is from 1.8 × 10^?4 to 1.8 × 10^?1 sec^?1. The rupture characteristics in stress/strain time space are analyzed on the three coordinate planes. Time and deformation separability are examined in a nonlinear-constitutive relation. Rupture data on the coordinate planes are described by the Bueche-Halpin theory in which time effects are considered through a small-deformation viscoelastic property. Fracture surface morphology and separation processes in the crack tip are related to rupture characteristics.     

Capture of submicrometer particles in a pressurized electrostatic precipitator

This study investigated the influence of gas pressure on the submicrometer particle capture performance of an electrostatic precipitator (ESP). Current-voltage characteristics and particle capture performance of the ESP were studied in air and in simulated flue gas (SFG) under 1, 2, and 3 atm. Using negative corona and air as the feed gas, the penetration of most particles of 40–400 nm in diameter decreased from 8 × 10^?4 ? 2 × 10^?2 to 2 × 10^?4 ? 1 × 10^?2 as pressure increased from 1 atm to 3 atm at constant current; and increased from 3 × 10^?5 ? 1 × 10^?3 to 2 × 10^?4 ? 1 × 10^?2 as pressure was elevated when the voltage was held roughly constant. Similar type of disparity under different pressures was also observed for positive corona and for SFG. Experiments set up to capture fly ash in the ESP showed that with constant current, higher pressure resulted in a higher initial charge fraction of the particles from the furnace, which could facilitate the penetration of fly ash particles. A semiempirical model was developed based on the Deutsch–Anderson equation and experimental data under 1, 2, and 3 atm to calculate the particle penetrations under high pressure. The total charge number on a particle (n') is calculated by incorporating the effects of current (I) and pressure (P) on relative weights of the diffusion charging number (n_diff) and field charging number (n_field), that is, n' = B₁(I,P)n_diff + B₂(I,P)n_field, where B₁(I,P) and B₂(I,P) are both empirical coefficients dependent on current and pressure. Experimental penetrations under 1.5 and 2.5 atm validated this model over the particle diameter range in 100–400 nm.

Copyright © 2016 American Association for Aerosol Research     

Kinetics of Solvent Extraction of Iron(III) from Sulfate Medium by Purified Cyanex 272 using a Lewis Cell

Abstract

The kinetics of the forward and backward extraction of the title process have been investigated using a Lewis cell operated at 3 Hz and flux or (F) – method of data treatment. The dependences of (F) in the forward extraction on [Fe³⁺], [H₂A₂]_(o), pH, and [HSO₄ ^?] are 1, 0.5, 1, and ?1, respectively. The value of the forward extraction rate constant (k _f ) has been estimated to be 10^?7.37 kmol^3/2 m^?7/2 s^?1. The analysis of the experimentally found flux equation gives the following simple equation: F _f =10^0.13 [FeHSO₄ ²⁺] [A^?], on considering the monomeric model of BTMPPA and the stability constants of Fe(III)‐HSO₄ ^? complexes. This indicates the following elementary reaction occurring in the aqueous film of the interface as rate determining: [FeHSO₄]²⁺+A^?→[FeHSO₄.A]⁺. The very high activation energy of 91 kJ mol^?1 supports this chemical reaction step as rate-determining. The negative value of the entropy change of activation (?94 J mol^?1 K^?1) indicates that the slow chemical reaction step occurs via the S_N2 mechanism.

The backward extraction rate can be expressed by the equation: F _b =10^?5.13 [[FeHSO₄A₂]]_(o) [H⁺] [H₂A₂]_(o) ^?0.5. An analysis of this equation leads to the following chemical reaction step as rate-determining: [FeHSO₄A₂]_(int)→[FeHSO₄A]+A_(i) ^?. However, the activation energy of 24 kJ mol^?1 suggests that the backward extraction process is intermediate controlled with greater contribution of the diffusion of one or the other species as a slow process. The equilibrium constant obtained from the rate study matches well with that obtained from the equilibrium study.     

Thermal shock resistance of flat plastic integrated circuit packages

Flat packages (FPs) were formed from epoxy molding compounds with various physical properties using a transfer molding machine. The compounds were prepared by changing kinds and amounts of additives and addition methods. The thermal shock test was carried out by the following procedures. The plastic package was soaked alternately in liquid nitrogen (?196°) and in liquid solder (200°) in the cycle of 140s. The median life to crack initiation was defined to be the cycles when half of the specimens exhibited crack initiation. According to linear fracture mechanics, the following expression was obtained relating the median life N, thermal stress σ_t, and strength σ_b; N = C/σ·(σ_b/σ_t)^m. We found the linear relation between logarithm of Nσ and logarithm of σ_b/σ_t for various packages, and estimated the values of C and m as 5 × 10⁴ MPa² and 5.5, respectively. The value of m was the same as that obtained for a dual-in-line package.     

Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR

An electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n-octane matrices at 80°K. |D| = 0.0359 cm^?1, |E| = 0.0079 cm^?1 for tetra phenyl porphyrin (H₂ TPP), |D| = 0.0432 cm^?1, |E| = 0.0037 cm^?1 for tetra (per-fluoro) phenyl porphyrin H₂T (per-F) PP, |D| = 0.0366 cm^?1, |E| = 0.0078 cm^?1 for tetra (para-chloro) phenyl porphyrin H₂T(P-Cl)PP, |D| = 0.0369 cm^?1, |E| = 0.0076 cm^?1 for tetra (para-methyl) phenyl porphyrin H₂T(P-Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels k_p, the ratio between the population rate constants A_p (at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated. k_x = (12 ± 2) × 10² sec^?1, k_y = (0.5 ± 0.1) × 10² sec^?1, k_z = (1.2 ± 0.4) × 10² sec^?1, A_x:A_y:A_z ? 0.63:0.01:0.33, W = (0.4 ± 0.1) × 10⁴ sec^?1 for H₂T(P-Cl)PP, k_x = (7 ± 2) × 10² sec^?1, k_y = (4 ± 1) × 10² sec^?1, k_z = (1.5 ± 0.5) × 10² sec^?1, A_x:A_y:A_z ? 0.56:0.31:0.13, W = (1.7 ± 0.4) × 10³ sec^?1 for H₂T(P-Me)PP.     

Similarity Solutions for the Population Balance Equation Describing Particle Fragmentation

Similarity solutions are obtained to the population balance equation describing particulate systems undergoing fragmentation. The solutions are restricted only by the requirement that the breakage rate of particles of volume v be of the form φ(v) = Av^b and the breakage distribution function of the form ω(u, v) = ?(v/u)/u, where u is the volume of the fragmenting particle. Under such conditions, the moments of the distribution asymptotically approach the form N_i(t) α t ^(1?i)/b , and the particle size distribution function is shown to obey a first-order linear ordinary integro-diflerential equation.

For the case ?(v/u) = γ(v/u)^γ?2, analytical solutions to the above equation were obtained. Complete solutions as well as asymptotic behavior are given. The results are potentially applicable to a wide range of particle fragmentation problems, including char/ash fragmentation during pulverized coal combustion, explosively generated aerosol formation, ore comminution, powder crushing and grinding, floe breakage, and crystallization kinetics.     

Rotating spherical interlayer (RSI) measurement of the dynamic mechanical properties of elastomers

An analysis of simple shear in a rotating spherical interlayer is presented. The theory provides design criteria and operating equations for a new method of measuring the dynamic mechanical properties of soft viscoelastic polymers. The storage component of the dynamic shear modulus G′(ω) = 3F₁hm²/2πr⁴(3 sin ? + sin³?) (ΔX_t ? K₁F₁) and the loss tangent than δ = [F₂(ΔX_t ? K₁F₁) ? K₂F₁F₂]/[F₁(ΔX_t ? K₁F₁)? K₂(F₂)²] are expressed in terms of the inner radius r, thickness, h, and are angle ? of sample extending from the rotational equator; the biaxial dynamometer compliances K₁, K₂; the imposed dynamometer displacement ΔX_t; and the spherical interlayer storage and loss forces F₁, F₂. New instrumentation involving a rotating spherical interlayer (RSI) transducer and a rotational accessory to the Instron provides measurements from 0.001 to 45 cycle/sec at temperatures from ?50° to 200°C. A comparison of RSI data, treated by time–temperature superposition, and literature values of dynamic response in polyisobutylene confirms both theory and method.     

Rheological properties of iron oxide particle suspensions

Viscosities of γ-Fe₂O₃ dispersions in epoxy resin, phenol resin, and polyvinyl butyral solutions are measured at shear rate D from 19.2 to 384 sec^?1. Volume fraction of γ-Fe₂O₃ in these dispersions ranges from about 0.002 to 0.03. The concentration dependence of relative viscosity η/η_s is closely represented by the Mooney equation. From this equation, intrinsic viscosity [η] of suspensions is found to decrease from 46.1 at D = 19.2sec^?1 to 14 at D = 384 sec^?1 for epoxy resin solution. The high [η] value indicates the existence of flocs containing immobilized liquid. By increasing the shear rate, the average floc size is reduced to point where at an infinite shear rate, only small clusters or possibly particles remain. Of the three polymers, the lowest [η] value is obtained in the dispersion of the phenol resin solution.     

First normal stress difference in capillary extrusion flow of nanometer calcium carbonate‐filled PLLA biocomposites

The nanometer calcium carbonate (nano‐CaCO₃)‐filled poly‐L ‐lactide (PLLA) biocomposites were prepared using a twin‐screw extruder. The first normal stress difference of the composites were measured by means of a capillary rheometer under experimental conditions with temperatures ranging from 170 to 200°C and shear rates varying from 50 to 10³ s^?1. The first normal stress difference (N₁) increased roughly linearly with increasing shear stress (τ_w). The sensitivity of the N₁ to τ_w increased with an increase of the die length–‐diameter ratio, and the N₁ value varied slightly with the filler weight fraction (?_f) as test temperature was constant. When the shear stress was fixed, the N₁ reached a minimum value for ?_f = 1%. The values of the N₁ of the composite melts decreased roughly linearly with a rise of temperature when the shear rate was constant. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Strain-induced crystallization,Part IV: Induction time analysis

The empirical equation, 1/t_i = Ae^Ei/RT, which expresses the exponential dependence of the reciprocal of crystallization induction time, t_i, has been analyzed and shown to be equivalent to the nucleation rate equations derived earlier in Part III (1). Consequently we have used the t_i measurements obtained earlier by Krueger and Yeh to calculate not only the nucleation rate enhancements but also the melting point elevations, the relative crystal thickness changes and molecular coil extension ratios of shear-crystallization polyethylene. It is shown that polyethylene when crystallized between 129 and 131°C at shear rates between 1.56 and 9.70 sec^?1 can have melting point increases of 4.2 to 7.2°C and crystal thickness decreases of 20 to 25 percent, when compared to those crystallized at 130°C in the quiescent state. The predicted “coil” extension in the melt just prior to shear-induced crystallization ranges between 21 and 36 percent. The results of these analyses as well as those on nucleation rates of polyethylene oxide are discussed in detail.     

Prediction of cure time for a rubber cement used for conveyer belt splicing

The evolution of bonding strength for a commercial cold vulcanizing rubber cement was determined using small–mscale simulated conveyer belt splicing. Peel and shear data obtained under isothermal conditions fit a modified Avrami model X = 1 ? exp(?kt^1/2), where X is the degree of ultimate shear or peel bond strength obtained and the rate constant k shows a typical Arrhenius type temperature dependence k = 42 exp(1670/T) min^1/2 for peel strength, and k = 57 exp(?2000/T) min^1/2 for shear strength. (T is the absolute temperature in K.) Bonding strength evolution under nonisothermal cure conditions can be estimated by integrating the general rate expression dX/dt = 0.5k²(1 ? X)/(?ln[1 ? X]).     

Comments on the reactivity of methoxy pentadecyl phenyl isocyanate isomers

The reactions of 2-methoxy-4-pentadecyl phenyl isocyanate and 4-methoxy-2-pentadecyl phenyl isocyanate with excess 2-ethyl hexanol originally reported by Ghatge and co-workers to follow zero order kinetics have been re-examined on the basis of their data and shown to follow more realistically the product catalyzed pseudo first order kinetics. The new rate constant, k_s (sec^?1) for the spontaneous reaction and k_p (li. mole^?1 sec^?1) for the product catalyzed reaction are found to be: k_s = 0.57 × 10^?6 and k_p = 34 × 10^?6 for 2-methoxy-4-pentadecyl phenyl isocyanate and k_s = 1.2 × 10^?6 and k_p = 82 × 10^?6 for 4-methoxy-2-pentadecyl phenyl isocyanate.