The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

Reversible heat effects in high temperature batteries: Transported entropy and thomson coefficients in cells with β″-alumina

The transported entropy and the Thomson coefficient for charge conducting ions are needed to predict reversible heat effects in batteries. Transported entropies and Thomson coefficients have been calculated from Seebeck coefficients of the cell Fe(s, T₁)|Me| β″ alumina | Me | Fe(s, T₂) for Na and K (Me). The result is S*_Na⁺ = 56 ± 3 J K⁻¹ mol⁻¹ at 500 K, with a Thomson coefficient τ_Na⁺ = 30 ± 2 J K⁻¹ mol⁻¹ in the temperature interval 333–773 K. The transported entropy of Na⁺ did not change by freezing Na at 370. The results for K⁺ are identical to those of Na⁺ within the accuracy of the experiments. The Thomson coefficient derived from measurements at different values of T₁ was consistent with the observed variation in emf with ΔT for a given T₁. The reversible heat changes at the electrodes have been calculated for sodium sulphur and potassium sulphur batteries. During discharge both batteries produce a net reversible heat, the production always being largest at the alkali metal anode. At the cathode, the heat effect becomes relatively small when the composition of Na and S is within the one phase region. A change in composition from the one phase to the two phase region is expected to lead to changes in local temperature gradients. The systems were described by the electric work method, a method which has practical advantages compared to other electrochemical methods.     

运用粒子图像测速仪研究双层桨搅拌槽内流体流动

The flow fields in a dual Rushton impeller stirred tank with diameter of 0.48 m （T） were measured by using Particle Image Velocimetry （PIV）. Three different size impellers were used in the experiments with diameters of D = 0.33T, 0.40T and 0.50T, respectively. The multi-block and 360° ensemble-averaged approaches were used to measure the radial and axial angle-resolved velocity distributions. Three typical flow patterns, named, merging flow, parallel flow and diverging flow, were obtained by changing the clearance of the bottom impeller above the tank base （C1） and the spacing between the two impellers （C2）. The results show that while C1 is equal to D, the parallel flow occurs as C2≥0.40T, C2≥0.38T and C2≥0.32T and the merging flow occurs as C2≤0.38T, C2≤0.36T and C2≤0.27T for the impellers with diameter of D=0.33T, 0.40T and 0.50T, respectively. When C2 is equal to D, the diverging flow occurs in the value of C1≤0.15T for all three impellers. The flow numbers of these impellers were calculated for the parallel flow. Trailing vortices generated by the lower impeller for the diverging flow were shown by the 10° angle-resolved velocity measurements. The peak value of turbulence kinetic energy （ k/V^2tip = 0.12-0.15 or above） appears along the center of the impeller discharging stream.     

Thermal effects in styrene-butadiene rubber at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for unvulcanized styrene-butadiene rubber (SBR) in the reference temperature range from 292 to 405 K and in the pressure range from 13.8 to 200 MN m⁻². The thermal effects were found to be a function of pressure and temperature. A curve fitting analysis showed that the empirical curve (∂T/∂P)=ab(ΔP)^b−1, described the experimental thermoelastic coefficients obtained from the experiments. The data were analysed by determining the predicted thermoelastic coefficients derived from the Thomson equation (∂T/∂P)=T_o/C_p. The experimental and the predicted Grüneisen parameter γ_T were also estimated. Close agreement was found at low pressure but differences were observed at higher pressures between the experimental and expected values for the thermoelastic coefficients and the Grüneisen parameter.     

Adsorption of methane/ethane mixtures on dry coal at elevated pressure

The binary adsorption characteristics of methane and ethane on dry coal to 40 atm pressure have been calculated from pure-component isotherms. In some coal seams, pressures exceeding 40 atm have been recorded and the methane sampled from the virgin coal often shows a few percent of ethane. The binary adsorption characteristics were calculated by employing the ideal adsorbed solution theory of Myers and Prausnitz, and experimentally-determined (Type I) pure gas isotherms at 0, 30 and 50 °C. The coal used in this investigation was high-volatile ‘A’ bituminous (hvab) from the Pennsylvania Pittsburgh seam. Gas nonideality was accounted for by replacing pressure with fugacity. Adsorption of methane on dry coal is purely physical; the isosteric heat of adsorption does not exceed 2.4 kcal/mol^* at 30 °C on the above coal. Isobars on the resulting binary equilibrium diagram exhibited an unexpected phenomenon of intersecting each other which might be attributable to the above nonideality considerations. The region of a few percent of ethane, which is of practical importance from the viewpoint of coal seams, was expanded and reduced to an equation: V(CH₄) = −21.52 + 7.18(VF) + 16.88(VF)² −0.395(P) − 0.00661(P)² + 0.824(T) − 0.00030(T)² + 0.928(VF)(P) − 0.858(VF)(T). V(Total) = 25.9 − 23.6(VF) + 0.655(P) − 0.00875(P)² − 0.795(T) + 0.743(VF)(T) where V(CH₄) and V(Total) = cm³(STP)CH₄ and total gas respectively adsorbed per g dry coal; VF = vol. fraction of methane as analysed at 1 atm (0.94 VF 1.0); P = seam pressure, atm (0 P 40); T=seam temperature, °C(−10 T 50).     

Reptation in polymer blends

Forward recoil spectrometry (FRES) was used to measure the tracer diffusion coefficients D*_PS and D*_PXE of deuterated polystyrene (d-PS) and deuterated poly(xylenyl ether) (d-PXE) chains in high molecular weight protonated blends of these polymers. The D*s were shown to be independent of matrix molecular weights and to decrease as M⁻², where M is the tracer molecular weight, suggesting that the tracer diffusion of both species occurs by reptation. These D*s were used to determine the monomeric friction coefficients ζ_0,PS and ζ_0,PXE of the individual PS and PXE macromolecules as a function of ф, the volume fraction of PS in the PS:PXE blend. Since ζ_0,PSζ_0,PXE at each ф, the rate at which a PS molecule reptates is much greater than that of a PXE molecule, even though both chains are diffusing in identical surroundings. Part of this difference may be due to the difficulty of backbone bond rotation of the PXE molecule. However, even when measured at a constant temperature increment above the glass transition temperature, ζ_0,PS and ζ_0,PXE were observed to be markedly composition dependent. In addition the ratio ζ_0,PS/ζ_0,PXE varied from a maximum of 4 × 10⁻² near ф=0.85 to a minimum of 5 × 10⁻⁵ for ф=0.0. These results show that intramolecular barriers do not solely determine the ζ₀s of the components in this blend. Clearly, the interactions between the diffusing chains and the matrix chains also influence ζ₀.     

Synthesis of novel chiral poly(methacrylate)s bearing urethane and cinchona alkaloid moieties in side chain and their chiral recognition abilities

Two types of new chiral methacrylates, cinchoninyl(2-methacryloyloxyethyl)carbamate (CIMOC) and cinchonidinyl(2-methacryloyloxy-ethyl)carbamate (CDMOC) were synthesized from 2-methacryloyloxyethyl isocyanate (MOI) and cinchona alkaloid such as cinchonine and cinchonidine, respectively. Radical polymerizations of CIMOC and CDMOC were performed under several conditions to obtain the corresponding polymers whose specific optical rotations ([]₄₃₅²⁵) were 84.0–89.0° and 0.39–0.72°, respectively. From the results of radical copolymerizations of RMOC (CIMOC and CDMOC, M₁) with styrene (ST, M₂) or methyl methacrylate (MMA, M₂), monomer reactivity ratios (r₁, r₂) and Alfrey–Price Q–e were determined: r₁=0.18, r₂=0.48, Q₁=0.53, e₁=0.92 for the CIMOC–ST system; r₁=0.53, r₂=0.26, Q₁=4.91, e₁=1.80 for the CIMOC–MMA system r₁=0.59, r₂=0.47, Q₁=0.86, e₁=0.33 for the CDMOC–ST system; r₁=0.28, r₂=0.59, Q₁=2.15, e₁=1.74 for the CDMOC–MMA system. The chiroptical properties of the copolymers were strongly influenced by co-units. Poly(RMOC)-bonded-silica gel as chiral stationary phase (CSP) was prepared for high performance liquid chromatography (HPLC). The CSPs resolved some racemates such as mandelic acid and trans-2-dibenzyl-4,5-di(o-hydroxyphenyl)-1,3-dioxolane by HPLC. The chiral recognition ability of poly(RMOC) may be due to the interaction between some cinchona alkaloid units and the racemates and/or to secondary and higher-ordered structures of the polymer.     

Comparison of evaluation procedures for the subcritical crack growth parameter n

The uncertainty in the determination of the exponent n in the equation of the subcritical crack velocity from four-point-bending experiments is investigated with respect to different evaluation methods. If the bending strength values are Weibull distributed, and the crack-extension parameter n is calculated by linear regression of the bending strength values of a number of experiments at different loading rates, an analytical solution can be given for the mean value and the standard deviation. It turns out that both the mean value and the standard deviation depend on the Weibull modulus m and the true value n₀. The analytical solution illustrates the essential features of this dependence on m and n₀. For other evaluation methods, e.g. the one proposed as the CEN standard, this dependence is investigated by a Monte-Carlo simulation for different crack-extension parameters n₀ and different Weibull moduli m. The standard deviation, which is calculated, is the theoretical lowest limit for certain evaluation procedures. By this, the estimation of the margin of error is put on a firm ground. Since the standard deviation increases with n₀, there is only a limited range in which n can be determined by four point-bending tests. A new evaluation method, which gives a better approximation than the method proposed as the CEN standard, is presented. The computational effort of this evaluation method is only slightly larger. It furthermore allows the number of experiments to be analytically calculated, which is necessary to obtain a certain accuracy.     

Thermoregulated phase transfer ligands and catalysis. III. Aqueous/organic two-phase hydroformylation of higher olefins by thermoregulated phase-transfer catalysis

A series of poly(ethylene oxide)-substituted triphenylphosphines, Ph_3−mP[C₆H₄-p-(OCH₂CH₂)_nOH]_m (PEO-TPPs; 1a m=1, 1b m=2, 1c m=3; N=m×n=8–25), have been prepared by the ethoxylation of mono-, di-, and tri-p-hydroxytriphenylphosphines. PEO-TPPs demonstrate an inverse temperature-dependent solubility in water, and possess distinct cloud points range from 26°C to 90°C.

Based on the clouding property of PEO-TPPs, a new line of aqueous/organic two-phase catalysis termed the thermoregulated phase-transfer catalysis (TRPTC) has been described. That is, the catalyst transfers into the organic phase to catalyze a reaction at a higher temperature, and returns to the aqueous phase to be separated from the products at a lower temperature. Application of this novel strategy to the rhodium-catalyzed two-phase hydroformylation of higher olefins gave desirable results with an average turnover frequency of 180 h⁻¹ for 1-dodecene. The TRPTC is suitable for carrying out a reaction with extremely water-immiscible substrate in the aqueous/organic two-phase system. Thus, the application scope of the classical two-phase catalysis has been widened.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

Effect of cooling rate and frequency on the calorimetric measurement of the glass transition

The glass transition of thermoplastics of different polydispersity and thermosets of different network structure has been studied by conventional differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC). The cooling rate dependence of the thermal glass transition temperature T_g measured by DSC, and the frequency dependence of the dynamic glass transition temperature T measured by TMDSC have been investigated. The relation between the cooling rate and the frequency necessary to achieve the same glass transition temperature has been quantified in terms of a logarithmic difference Δ=log₁₀[|q|]−log₁₀(ω), where |q| is the absolute value of the cooling rate in K s⁻¹ and ω is the angular frequency in rad s⁻¹ necessary to obtain T_g(q)=T(ω). The values of Δ obtained for various polymers at a modulation period of 120 s (frequency of 8.3 mHz) are between 0.14 and 0.81. These values agree reasonably well with the theoretical prediction [Hutchinson JM, Montserrat S. Thermochim Acta 2001;377:63 [6]] based on the model of Tool–Narayanaswamy–Moynihan with a distribution of relaxation times. The results are discussed and compared with those obtained by other authors in polymeric and other glass-forming systems.     

Diffusional deposition from a fluid flowing radially between concentric, parallel, circular plates

We have made a theoretical study of the diffusional losses of particles from a fluid flowing radially inward between concentric, parallel, circular plates of radius, R_o. The relative number of particles remaining in the fluid at a distance, r, from the axis of the plates is

where γ = 4πD (Ro² − r²)/3Qh, D is the diffusion coefficient of the particles, Q is the volumetric flow rate, and 2h is the separation between the plates. The practical application of the system is discussed.

The same equation applies to parallel flow through a duct of rectangular cross-section if γ = 4DBl/3Qh, where B and l are respectively the duct width and length. It is more accurate than equations now in use to describe this process.     

Tracer diffusion of aromatic hydrocarbons in n-hexane up to the supercritical region

Tracer diffusion coefficients are determined with the Taylor-Aris dispersion method for benzene, toluene, p-xylene, mesitylene, naphthalene and phenanthrene in liquid n-hexane along the vapour-liquid coexistence curve from 333.2 to 485.4 K and in supercritical n-hexane at 507.4, 522.0, 533.3, 543.2K and several pressures. A rough-hard-sphere model is found to represent quite well (to within ± 6%) the observed tracer diffusivities in the density region where computer simulation results for D₁₂^SHS/D₁₂^E are available, i.e. 1.5 V/V₀ 3. Furthermore, Hildebrand's free volume model together with the excluded-volume effect provides the basis for a general linear relationship between D₁₂V_C12 and V for tracer diffusion in liquid n-hexane up to its critical temperature. For diffusion in the supercritical region two definitions of reduced tracer diffusivity, one based on the rough-hard-sphere theory of tracer diffusion and the other on the extension of Helfand-Rice corresponding state principle for self-diffusion, permit generalized correlations that are capable of representing the experimental results in both supercritical n-hexane and carbon dioxide to within ±4% on average.     

The anodic dissolution of iron—V. Some observations regarding the influence of cold working and of annealing on the two anodic reactions of the metal

Under conditions, where two anodic current regions, I₂ and I₂, were distinct in the Tafel plots of the iron electrode, the reaction orders with respect to pH were determined. In solutions containing chloride or bromid, pH ca 3–5, the reaction order for I₁(p_1,pH) was close to 1, while that for I₂(p_2,pH) assumed positive or negative values or even values changing from positive to negative over the pH-range. The numerical values were small, 0·2–0·3. Only lightly cold-worked iron was used in this group of experiments.

In another group of experiments only involving acetate containing solutions both cold-worked and annealed electrodes were employed. Until the influence of acetate became negligible at low pH, the effect of the treatment was largely limited to dissolution rates. The characteristic parameters at pH ca 4 were: for the I₁ reaction: b₁ = 30 mV, p_1,pH = 1·7 and p_1,Ac¹ (the reaction order for Ac) = −0·7; for the p₂ reaction: b₂ = 110 to 130 mV, p_2,pH = 0·2 and p_2,Ac = −0·2 to −0·3.

At lower pH the influence of acetate gradually disappeared, and higher values of b₁ and lower values of p_1,pH were then noted for the annealed metal. The I₂ reaction could not be followed here.

The transition between the I₁ and the I₂ reaction was studied at pH ca 4, and some deviation from earlier experience was noted for strongly cold-worked iron.     

Interdiffusion in blends of polystyrene and polymethylstyrene studied by light scattering after temperature jumps across the phase boundary

We describe a simple light scattering set-up for measuring interdiffusion coefficients D in polymer blends by generating spinodal decomposition and subsequent dissolution after temperature jumps across the phase boundary. In blends of polystyrene and polymethylstyrene (random copolymer of 60% m-methylstyrene and 40% p-methylstyrene) D values were obtained between 10⁻¹¹ and 10⁻¹⁵ cm²s⁻¹ at temperatures up to 50 K above the upper critical solution temperature. The results are discussed in relation to tracer diffusion in the same system.     

Dynamic mechanical spectra of poly(itaconic acid esters) containing phenyl and cyclohexyl rings

The dynamic mechanical response of a series of poly(itaconic acid esters), in which the ester group, ---COOR, has R = (CH₂)_n ø with n = 0, 1, 2 and ø is either a phenyl or cyclohexyl ring, was studied over the temperature range 90 to 425K. In each case the glass transition temperature T_g, of the cyclohexyl derivative is higher than the corresponding phenyl derivative, and T_g also decreases as n increases. A β-transition, located in both the phenyl and cyclohexyl series, is attributed to motion of the ester groups. In addition the cyclohexyl polymers exhibit a prominant γ-transition caused by cyclohexyl ring movement and there is also a δ-transition in this series which is believed to be a precursor of the γ-transition.     

Nanosized perovskite-type oxides La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) for the catalytic removal of ethylacetate

Nanometer perovskite-type oxides La_1−xSr_xMO_3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m² g⁻¹, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn⁴⁺ and Mn³⁺ in La_1−xSr_xMnO_3−δ and Co³⁺ and Co²⁺ in La_1−xSr_xCoO_3−δ, Sr substitution induced the rises in Mn⁴⁺ and Co³⁺ concentrations; adsorbed oxygen species (O⁻, O₂⁻, or O₂²⁻) were detected on the catalyst surfaces. The O₂-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H₂-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h⁻¹, the catalytic activity (as reflected by the temperature (T_100%) for EA complete conversion) increased in the order of LaCoO_2.91 (T_100% = 230 °C) ≈ LaMnO_3.12 (T_100% = 235 °C) < La_0.6Sr_0.4MnO_3.02 (T_100% = 190 °C) < La_0.6Sr_0.4CoO_2.78 (T_100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn⁴⁺/Mn³⁺ and Co³⁺/Co²⁺ ratios), and rich lattice defects of the nanostructured La_1−xSr_xMO_3−δ materials.     

Simultaneous desulfurization and denitrification of sintering flue gas via composite absorbent

Experiments on simultaneous absorption of SO_2 and NO_X from sintering flue gas via a composite absorbent NaClO_2/NaClO were carried out. The effects of various operating parameters such as NaClO_2 concentration(ms), NaClO concentration(mp), molar ratio of NaClO_2/NaClO(M), solution temperature(TR), initial solution pH, gas flow(Vg) and inlet concentration of SO_2(CS) and NO(CN) on the removal efficiencies of SO_2 and NO were discussed. The optimal experimental conditions were determined to be initial solution pH = 6, TR=55 °C and M = 1.3 under which the average efficiencies of desulfurization and denitrification could reach99.7% and 90.8%, respectively. Moreover, according to the analysis of reaction products, it was found that adding NaClO to NaClO_2 aqueous solution is favorable for the generation of ClO_2 and Cl_2 which have significant effect on desulfurization and denitrification. Finally, engineering experiments were performed and obtained good results demonstrating that this method is practicable and promising.     

Numerical simulations of slip correction

Stoke's law

F=6πηRυ

is valid only in liquids. In order to apply this law to particles suspended in air, the slip correction is needed, especially for particles with diameters less than 1 μm.

The slip correction is included in Stoke's law by

with and the Knudsen number (ratio of the particle radius to the mean free path of the gas molecules), η the viscosity of the gas, R the particle radius and and υ the velocity of the particle. For large Knudsen numbers, this equation reduces to

In the present work a simple Monte-Carlo simulation model is used to determine slip corrections in the free molecule regime (Knudsen number Kn 1: The velocity of the air molecules are assumed to follow a Maxwellian distribution. The particle moves steadily in the gas, and the molecules impinge on its surface. The impaction points are distributed uniformly over the particle's surface. A simple criterium shows whether a molecule can in fact hit the surface at the selected point. If so, the transferred momentum is calculated. After sufficient iterations the slip correction is obtained by comparing the total transferred momentum with the expression for the Stokes drag force. Since only the free molecule regime is considered, the slipcorrection equals + β.