Mechanism of fracture in glassy polymers. IV. Temperature rise at the tip of propagating crack in poly(methyl methacrylate)

The temperature rise at the moving crack tip in poly(methyl methacrylate), resulting from the dissipation of the energy of crack propagation has been calculated. At velocities below 1 cm./sec., conduction of heat away from the crack plane into the bulk polymer appears to prevent any appreciable temperature increase.     

Kinetic studies of the deactivation of O2(1Σg+) and O(1D)

The kinetics of the deactivation of O₂(¹Σ_g⁺) is studied in real time. O₂(¹Σ_g⁺) is generated in this system by the O(¹D) + O₂ reaction following O₃laser flash photolysis in the presence of excess O₂, and it is monitored by its characteristic emission band at 762 nm. Quenching rate constants were obtained for O₂, O₃, N₂, CO₂, H₂O, CF₄and the rare gases. Since O(¹D) is the precursor for the formation of O₂(¹Σ_g⁺), the addition of an O(¹D) quencher effectively lowers the initial concentration of O₂(¹Σ_g⁺). By measuring the initial intensity of the 762 nm fluorescence signal, the relative quenching efficiencies were determined for O(¹D) quenching by N₂, CO₂, Xe, and Kr with respect to O₂; the results are in good agreement with literature values.     

The mathematical modelling of a production scale sequential continuous chromatographic refiner unit

Summary A plate to plate mathematical model of a sequential gas-liquid chromatographic separator used for the continuous separation of volatile organic mixtures has been extended to include theoretically determined temperature, pressure and concentration effects. A comparison has been made of predicted values with experimental results obtained on a 12 column (7.6 cm o.d. ×61 cm) sequential continuous chromatograph when separating an equivolume mixture of Arklone P-Genklene P at feed rates of up to 1400 cm³ hr^–1.     

Stochastic matrices over cones

The notion of a stochastic operator in an ordered Banach space is specialized to a finite dimensional ordered real vector space. The classical limit theorems are obtained, and an application is made to non-homogeneous Markov chains. Finally, groups of nonnegative matrices are discussed.     

An entanglement model for the dependence of fracture surface energy on molecular weight

Over the last decade, empirical evidence has indicated that the effective surface energy γ associated with the fracture of noncrystalline is a linear function of the reciprocal of the viscosity–average molecular weight: \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma = \gamma _\infty - b\bar M_v ^{ - 1} $\end{document}. For poly(methyl methacrylate), data of J. P. Berry, G. C. Berry and Fox show that gamma; ～ 0 at about the same value of M?_v that corresponds to the polymer chain-entanglement length. From this fact, we have developed an entanglement network model for fracture, that bears a resemblance to F. Bueche's entanglement model for the melt viscosity of bulk polymers. Our model allows for the expression of the previously empirical constants, γ_∞ and b, in terms of molecular parameters: \documentclass{article}\pagestyle{empty}\begin{document}$ {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } \mathord{\left/ {\vphantom {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } {\bar M_{\rm s} }}} \right. \kern-\nulldelimiterspace} {\bar M_{\rm s} }} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ b = 2({{\bar M_v } \mathord{\left/ {\vphantom {{\bar M_v } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }})\gamma _\infty M_{\rm f} $\end{document} where M?_n and M?_f are the number-average molecular weights of the polymer and of the free chain ends, M?_v is the viscosity-average molecular weight, γ_s is the average fracture-energy per entanglement in the craze volume, A_s is the average cross-sectional area of the polymer chain, Z_c and ρ_c are the thickness and density of crazed material on the fracture surface, respectively; M?_s is the average strand molecular weight between entanglements, and N_A is AvogadrO's number.     

2-methoxyethanol as a solvent for conductometric acid-base titrations

Conductometric titrations of a series of organic acids in 2-methoxyethanol were performed with 1,3-diphenylguanidine (DPG) as titrant. For benzoic, p-chlorobenzoic and picric acids, phenylphenol and barbital, excellent recoveries were obtained from well-defined conductance vs. volume plots. Results for the dicarboxylic phthalic and adipic acids were also good. However, the titration curves for the difunctional salicylic and p-hydroxybenzoic acids were not clearly defined. The results are discussed and compared with cnductometric titrations of acids in other non-aqueous solvents. Several determinations of electrolyte conductance as a function of concentration revealed that, as expected, the selected substances are weak electrolytes in methoxyethanol.