Kinetics and equilibrium swelling of gelatine gels

The swelling features of gelatine gels in water (good solvent) were studied as a function of thermodynamic conditions of sol—gel transition and ripening. It is shown that the degree of equilibrium swelling Q_e varies with the volume fraction of the polymer in a casting solution φ_o in accordance with the prediction of the classic theory: Q_e φ_o^−0.4. Q_c, as a function of the gelation temperature T_g, the ripening time t_r and φ_o, can be rescaled and described by the single empirical equation: Q_e T_g^−x t_r^−yφ_o^−0.4, where x = 0.1, y = 0.15 for wet gels and X = −0.5, y = 0.04 for dried gels. The kinetics of macroscopic swelling is described by the equation of Peters and Candau, with values of collective diffusion coefficients being in good agreement with values obtained by other workers via photon correlation spectroscopy.     

Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

Reply to comments on the need to reconsider traditional free volume theory for polymer electrolytes

New aspects of the defect diffusion model (DDM) are presented. First, it is shown that if the correlation volume exhibits two dimensional scaling, e.g. grows in two dimensions more rapidly than in a third orthogonal direction, the standard Vogel relation is obtained. Second, it is pointed out that, independent of the dimensionality, ∂ ln σ/∂P should be proportional to ∂ ln σ/∂ ln T where the proportionality constant is −∂ ln T_c/∂P. It is shown that both of these results are consistent with the temperature and pressure variation of the electrical conductivity for 20:1 PPG:LiCF₃SO₃ below about 1.3 times the glass transition temperature, T_g. Finally, the DDM is compared with the free volume theory (FVT) of Dlubek et al. who have reconsidered “traditional” FVT and presented a formalism where the free volume is not proportional to the macroscopic volume. One aspect of the new FVT, which is difficult to understand is that the compressibility of the occupied volume is larger than the compressibility of the free volume.     

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.     

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).     

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.     

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.     

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.     

Liquid-phase methanol synthesis in apolar (squalane) and polar (tetraethylene glycol dimethylether) solvents

The kinetics of the three-phase methanol synthesis over a commercial Cu–Zn–Al₂O₃ catalyst were studied in an apolar solvent, squalane and a polar solvent, tetraethylene glycol dimethylether (TEGDME). Experimental conditions were varied as follows: P=3.0–5.3 MPa, T=488–533 K and Φ_vG/w=7.5×10⁻³–8×10⁻³ Nm³ s⁻¹kg⁻¹_cat. The nature of the slurry–liquid influences the activation energy and the kinetic rate constant by interaction between adsorbed species and solvent and by competitive adsorption of the solvent on the catalyst surface. The rate of reaction to methanol observed in TEGDME appeared to be about 10 times lower than in squalane. TEGDME reduces the reaction rate, which is a disadvantage for its use as a solvent.     

Dielectric relaxation due to absorbed water in various thermosets

The dielectric relaxation due to absorbed water has been studied with a number of epoxies and other thermosets. In all cases, the absorbed water relaxation strength, as measured by both the dielectric-constant increase and the increase in area under the ″ versus 1/T curve, seems to be attributable to the relaxation of water dipoles and not to Maxwell-Wagner-Silars effects. The activation energies obtained are in the 11–16 kcal mol⁻¹ range. The relaxation strengths observed show that the water molecules manifest roughly 70–100% of their free-state polarizability. In general, the dielectric constant increase per 1 wt% of water absorbed is given to a good approximation by 4.0[(dry) + 2]² pf/T where f is the fractional polarizability of water in the polymer to its free-state value, found to be 0.7 to 1.0 for most thermosets, and and T are the density and temperature.     

Solution properties of xanthan. Light scattering and viscometry on dilute and moderately concentrated solutions

Elastic and quasi-elastic light-scattering, viscometric and rheological studies are given for solutions of the microbial polysaccharide Xanthomonas campestris (xanthan) in aqueous 0.62N NaCl for polymer concentrations from 0.03 to 2.2 g kg⁻¹. The observed negative ∂ln[η]/∂ln T is interpreted as a decrease of the persistence length with increasing T. The behaviour in moderately concentrated solutions (2<[η]c<25) reveals intermolecular association, leading to gel formation in the extreme case. The effect of the association on the viscometric and light-scattering data is discussed. It is concluded that the early stages of association involve structure with the chain axes nearly parallel, but that larger, particulate-like structures develop with increasing c, eventually leading to gel formation under certain conditions.     

Surface dynamics during latex film formation

Surface dynamics during latex film formation has been investigated theoretically and experimentally by atomic force microscopy. The peak-to-valley distance, y(t), of the latex particles in the surface plane of the latex film decayed exponentially with time during film formation. A theoretical relationship between y(t) and time, t, is given by y(t)=y(0) exp[−t/τ], where y(0) is the value of y(t) when t is zero. τ is a characteristic constant related to the nature of polymer, the particle radius, the surface diffusion coefficient and the temperature. The relationship between the surface diffusion coefficient, D_s, y(0), the radius of the latex particles, R, temperature, T, and τ is given approximately by D_s=1.2×10⁻²⁰y(0)²[2R−y(0)]²T/τ (cm²/s), where the units are manometers for y(0) and R, kelvin for temperature, and seconds for τ. By measuring the decay of y(t) with time, the surface diffusion coefficient can be obtained. The surface diffusion coefficient for a poly(methyl methacrylate-co-butylacrylate) (50:50) copolymer latex film was found to be A×10⁻¹³ cm²/s, A is temperature-dependent.     

Distribution of sulphur in one-dimensional pulverized-coal flames

Results of experiments to determine the distribution of fuel sulphur in one-dimensional pulverized-coal flames are presented for two high volatile A bituminous coals, one pulverized into three size fractions, and one subbituminous A coal. A complete determination of the sulphur fed into the flame was obtained through measurement of SO₂, H₂S, COS, CS₂, and solids sulphur. SO₂ is the predominant gas-phase species followed by H₂S with COS and CS₂ being present in smaller amounts. Sulphur is released from smaller particles more rapidly than from larger ones. Sulphur release parallels, to some extent, nitrogen release except at the longer residence times for the subbituminous coal and one of the bituminous coals. A substantial fraction of the sulphur contained in these coals is inorganic. First-order rate constants for sulphur release from the solid are presented. The effects of internal mass transfer on the kinetics are presented for one of the bituminous coals by considering the sulphur release process to consist of a first-order devolatilization reaction occurring in parallel with diffusion of the sulphur to the particle surface and first-order deposition back to the solid matrix. Particle size effects are accounted for in the model, and the data on solids sulphur are used to obtain activation temperatures for the devolatilization reaction and the deposition reaction of 29 900 and 31 400 K, respectively.     

Polar interaction in a cyanated poly(ether sulfone)-modified polycyanurate

Low molecular weight cyanated poly(ether sulfone) (CPES, Mn=3200) was prepared, and cured with bisphenol A dicyanate (BPADCy). The resulting polycyanurates of different compositions show an S-shaped T_g-composition curve. This unexpected S-shaped curve is interpreted in term of the polar interaction between poly(ether sulfone) and s-triazine rings formed by polycyclotrimerization of aromatic dicyanates. Separate study on u.v. spectra of mixture model compounds suggests that this polar interaction belongs to an n–π* interaction between the lone pair electrons of the N-atoms in the s-triazine ring and the π*-orbital of the phenylene rings neighbouring to the sulfone linkage. I.r. study on the cured polycyanurates indicates that this polar interaction causes the shift of the —C=N stretching from 1564 to 1580 cm⁻¹.     

The condensation/polymerisation of dimethyl siloxane fluids in a three-phase trickle flow monolith reactor

For the production of siloxane fluids, the viability of using a multi-channel monolith as a catalyst support system in a three-phase reactor has been studied. The catalyst was tripotassium phosphate (K₃PO₄). Experiments were performed in a single-channel flow reactor (15 mm i.d. and 500 mm catalyst coated length). The rate of reaction was followed by monitoring the disappearance of the hydroxyl group (–OH). Reaction experiments were performed at a hydroxyl group concentration range from 150 to 170 mol m⁻³, T=373–413 K and P=7.9 kPa with a nitrogen purge. The maximum temperature of operation was restricted to 413 K to avoid the formation of undesirable by-products. In the regime controlled by chemical kinetics, reaction was of an apparent first order with respect to –OH concentration, and in the apparent rate constant, the pre-exponential factor was 4.19×10⁻⁴ ms⁻¹, and the apparent activation energy was 16.1 kJ mol⁻¹. These are only valid for the operating pressure and purge gas flowrate used, as both of these are shown to affect water removal from the liquid phase and, hence, reaction rates. Mass transfer coefficients from the liquid to the catalyst surface were estimated and these increased rapidly with flowrate and were higher than expected for a falling liquid film.     

Conductivity, charge transfer and transport number—an ac-investigation of the polymer electrolyte LiSCN-poly(ethyleneoxide)

In this paper a series of impedance measurements in the frequency range 10⁻⁴−2 × 10⁵ Hz and in the temperature range 20–170°C is reported for the cell: Li-metal/LiSCN [dissolved in poly (ethyleneoxide)]/Li-metal. On the basis of the measurements a whole range of electrical properties such as the conductivity, the charge transfer resistance, the transport number for the Li⁺-ion, the double layer capacity and the dielectric constant were determined for the polymer complex. The most important findings were (1) two regions with linear log σ vs 1/T plots and a transition temperature between the regions of 80°C and (2) the fact that both ions were mobile in the polymer complex with the Li⁺-ion having a transport number of 0.54 independent of temperature.     

Correlation between equation of state and temperature and pressure dependence of self-diffusion coefficient of polymers and simple liquids

Correlation between the equation of state and the temperature dependence of the self-diffusion coefficient D for polymers such as polystyrene (PS) and polydimethyl siloxane (PDMS) and simple liquids such as argon, methane and benzene and the pressure dependence of D for oligomers such as dimethyl siloxane (DMS) and simple liquids such as cyclohexane and methanol has been examined based on the equation of state derived previously. The experimental data used were published by Antonietti et al. and McCall et al. for polymers, by McCall for linear dimethylsiloxanes and by Jonas et al. and Woolf et al. for simple liquids. The expression for D in this work is given by

where A₁(M) is a function of molecular weight M_w, C₁(T) and P₁(T) are functions of temperature and B₁, n₁ and m₁ are constants determined experimentally. For simple liquids, the values of n₁ obtained range from 0.3 to 1.2, with an average , and m₁ is in the range 0.5–1.2, with . For polymers, values of n₁ are in the range 2.5–7.0 for PS and 0.5–1.3 for PDMS and m₁ for DMS is in the range 0.8–1.0. The relation Dη/T = f(M) is found to be useful for simple liquids over a wide range of temperature including the critical region and for pressures up to ≈5 kbar

1 kbar = 100 MPa There is a close correlation between ln(D/T) and _p and β_T through ln(D/T)ln D_c−⁻¹_p−β⁻¹_T, where D_c is D at the critical temperature and _p and β_T are the thermal expansion coefficient and compressibility, respectively. The molecular weight dependence of D for polymers and simple liquids is discussed based on the experimental data and recent theory of Doi and Edwards. A new model for the mechanism of self-diffusion in the liquid state is proposed.     

The equilibrium melting temperature of cis-polyisoprene

The equilibrium melting temperature T°_m of cis-polyisoprene (Hevea natural rubber) has been determined to be 35.5°C at atmospheric pressure. The optical ‘turbidimetric’ technique developed to obtain the melting data, discussed in this paper, utilized unpolarized light and was free of complications (presumably involving melt strain) encountered with polarized light techniques, but was found to be consistent with that and other techniques. The effect of variables such as heating rate and crystallization time were considered. Two independent methods of extrapolation of the T_m data to evaluate T°_m produced values in the range T°_m = 35.5° ± 0.3°C. The fold surface free energy σ_e was also estimated, by two independent methods, to be 0.024 J m⁻².     

Parametric studies on devolatilization of a subbituminous coal in a reactive gas environment

A laboratory scale fixed bed coal gasifier was set up to simulate the conditions existing in the devolatilization zone of an air-blown, fixed-bed coal gasifier. Devolatilization behaviour of a subbituminous coal was evaluated in the temperature range 350 °C to 550 °C and at pressures 30, 300 and 375 psig. Three feed coal particle sizes, (−2, +1), (−4, +3) and (−9, +6)mm, were studied. The gas feed was a synthetic mixture of composition similar to that leaving the gasification zone of a fixed bed gasifier and contained 30% by volume of steam. Devolatilization runs were conducted over coal residence times of 5, 10, 20 and 30 min durations. The gas evolution rates showed a peak around 5 min from the start of a run and most of the gas evolution tapered off just under 30 min. Thirty key components in the tars were quantified and these included aliphatic and aromatic homologues, as well as sulphur and nitrogen substituted structures. The molecular weights of the tar samples showed a maximum between 300 and 500. A first order kinetic model applied to the total weight loss data yielded activation energies in the range 4 to 11 kcal mol⁻¹. Differential equations for obtaining concentration profiles for tar and gas inside the coal particle were solved numerically. From these calculations it was concluded that the pressure buildup (due to evolution of tar and gas) inside the coal particle was higher for larger particles, at a given external pressure, but decreased with external pressure. The concentration of tar inside the particle did not appear to be sensitive to low pressures (around 1 atm), but increased in the higher range of pressure (above 20 atm) and also with particle size.