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The anisotropy of the swelling of rubber is examined both theoretically and experimentally. The Flory theory is extended to account for anisotropic swelling, allowing the determination of the average molecular weight between cross-links for rubber with swelling anisotropy for the first time. In addition, specimens from five commercial rubbers manufactured using either compression-moulding or sheet-rolling processes are swollen in appropriate organic solvents. Their linear dimensions and mass are carefully recorded before swelling, in the swollen state, and after drying, to obtain three linear swelling ratios which can differ by up to 10% within each specimen. Compression-moulded rubbers are shown to be transversely isotropic after moulding, whereas rolled rubbers exhibit full anisotropy, with different swelling ratios in all three directions. None of the rubbers examined were found to be truly isotropic. The new anisotropic swelling theory is applied to the experimental data to determine the average molecular weight between cross-links, which is determined as up to 0.5% larger than the value obtained using the Flory isotropic swelling theory. [ABSTRACT FROM AUTHOR]

Data on density, ρ , speed of sound, c , and refractive index, n D , have been reported at (293–303.15) K for the N , N -dimethylacetamide (DMA) + CH 3 CO(CH 2 ) u − 1 CH 3 ( u = 1, 2, 3) systems, and at 298.15 K for the mixture with u = 5. These data have been used to compute excess molar volumes, V m E , excess adiabatic compressibilities, κ S E , and excess speeds of sound c E . Negative V m E values indicate the existence of structural effects and interactions between unlike molecules. From molar excess enthalpies, H m E , available in the literature for N , N -dimethylformamide (DMF), or N -methylpyrrolidone (NMP) + n -alkanone systems, it is shown: (i) amide-ketone interactions are stronger in DMF systems than in those with NMP; (ii) they become weaker when u increases in mixtures with a given amide. Structural effects largely contribute to H m E and are more relevant in mixtures containing NMP. The application of the Flory's model reveals that the random mixing hypothesis is valid in large extent for DMF solutions, while NMP systems are characterized by rather strong orientational effects. From values of molar refraction and of the product P int V m (where P int is the internal pressure and V m the molar volume), it is concluded that dispersive interactions increase with u , or when DMF is replaced by DMA in mixtures with a fixed ketone. [ABSTRACT FROM AUTHOR]

Interactions and structure of organic carbonate + alkane, and 1-alkanol + organic carbonate mixtures have been investigated by means of a set of molar excess functions, enthalpies ( H m E ), volumes ( V m E ), isobaric heat capacities, ( C p m E ) or entropies; and considering internal pressure ( P int ); liquid-liquid equilibria or permittivity data. In addition, the mentioned systems have been studied using the Flory model and the concentration-concentration structure factor S CC ( 0 ) , formalism. The mixtures under consideration are characterized by dipolar interactions and by homocoordination (that is, by interactions between like molecules). In systems with a given solvent, dipolar interactions are weakened in the order: propylene carbonate (PC) > dimethyl carbonate (DMC) > diethyl carbonate (DEC). Comparison of mixtures containing DMC or DEC with those involving 2-propanone or 3-pentanone shows that dipolar interactions are not determined merely by values of the dipole moment, but they also depend on the size group. The enthalpies of the alkanol-carbonate interactions have been evaluated from calorimetric data. They are stronger in DMC solutions, and become weaker when the alcohol size increases in mixtures with a given carbonate. Application of the Flory model to 43 systems of the type 1-alkanol + carbonate provides a mean relative standard deviation for H m E equal to 0.107. Results reveal that orientational effects decrease in the order DEC > PC > DMC. Orientational effects are particularly relevant in methanol or ethanol + DEC mixtures. Interestingly, the mentioned effects are weaker in 1-alkanol + DMC mixtures than in DMC + alkane systems. A similar trend is observed in DEC solutions when the considered alcohol is longer than ethanol. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2-alkanol + n -alkanone, + acetophenone, + linear or cyclic ether, or organic carbonate mixtures were investigated. • Solvent-solvent interactions are determinant in systems with n -alkanones or linear carbonates. • Interactions between alcohol molecules are determinant in mixtures with linear monoethers. • Flory model and Kirkwood-Buff integrals have been applied. • Orientational effects are stronger in solutions with linear monoethers. The mixtures 2-propanol or 2-butanol + n -alkanone, or + acetophenone, or + linear monoether, or + cyclic ether, or + linear organic carbonate, or + propylene carbonate have been investigated using thermodynamic data, and in terms of the Flory theory, and the Kirkwood-Buff integrals. The data considered are: excess molar enthalpies (H m E), volumes, entropies, and the temperature dependence of H m E. The enthalpy of the 2-alkanol-solvent interactions have been determined, and the different contributions to H m E discussed. It is shown that H m E values of the 2-alkanol (fixed) + n -alkanone, or + linear carbonate mixtures change in the same manner that for n -alkanone, or linear carbonate + n -alkane (fixed) systems. In contrast, H m E values of 2-alkanol (fixed) + linear monoether or + n -alkane mixtures change similarly. This set of results suggests that solvent–solvent interactions are determinant in systems with n -alkanone or linear carbonate, while interactions between alcohol molecules are determinant in mixtures with linear monoethers. According to the Flory model, orientational effects in systems with a given 2-alkanol become weaker in the sequence: linear monoether > linear organic carbonate > n -alkanone, and are stronger in solutions with a cyclic monoether than in those with cyclic diethers, and in systems with acetophenone or propylene carbonate than in the mixtures with the corresponding linear solvents. Results obtained from the Kirkwood-Buff integrals are consistent with these findings. The application of Flory model reveals that orientational effects are similar in systems with 1- or 2-alkanols, with the exception of solutions with linear monoethers, where such effects are stronger in mixtures containing 1-alkanols. For the examined systems, the formalism of the Kirkwood-Buff integrals makes no meaningful distinction between solutions with 1-alkanols or 2-alkanols. [ABSTRACT FROM AUTHOR]

This work reconsiders a refined Flory model designed to approximately describe molar-mass distributions obtained from irreversible step-growth polymerizations of α, ω-heterodifunctional molecules with competing cyclization. By comparing to both quantitative analytical and accurate numerical solutions, we show that the refined Flory model is a reasonable approximation that allows for an intuitive understanding of the chemical system discussed. Building upon this insight, we present a recursive transformation of the refined Flory model by probabilistic means resulting in Szymanski's quantitative description of molar-mass distributions. [ABSTRACT FROM AUTHOR]

In this work we used the Flory theory of liquid mixtures for determining the thermal parameters such as excess thermal expansion coefficients α E , and isothermal coefficient of pressure excess molar enthalpy ( ∂ H m E / ∂ P ) T , x , of the binary mixtures formed by vinyl acetate and benzyl acetate + o -xylene, or m -xylene, or p -xylene at (303.15 and 313.15) K. From these data the acoustical parameters such as available volume ( V a ), isothermal ( K / ), isobaric ( K ), and isochoric acoustical parameters ( K // ), isochoric temperature coefficient of the internal pressure ( X ), and Moelwyn-Hughes parameter ( C 1 ), have been calculated. The excess thermal expansion coefficient α E , for the binary mixtures of benzyl acetate + o -xylene and vinyl acetate + m -xylene are negative in x = 0.2434 and x = 0.9602, respectively, and positive for all mole fractions and increase with increasing temperatures from (303.15 and 313.15) K. The isothermal coefficient of pressure excess molar enthalpy, ( ∂ H m E / ∂ P ) T , x , for vinyl acetate + o -xylene, + p -xylene and benzyl acetate + m -xylene,+ p -xylene are negative and decrease with increasing temperatures from (303.15 and 313.15) K. The isothermal coefficient of pressure excess molar enthalpy, ( ∂ H m E / ∂ P ) T , x , for a binary mixture of benzyl acetate + o -xylene is positive and increases with increasing temperatures from (303.15 and 313.15) K. [ABSTRACT FROM AUTHOR]

Abstract: Experimental densities, ρ, and speeds of sound, u, have been measured at (293.15–303.15)K for the systems methanol, 1-butanol or 1-decanol+3,6,9-trioxaundecane using a vibrating-tube densimeter and sound analyzer Anton Paar model DSA-5000. These values were used to calculate excess molar volumes, , excess adiabatic compressibilities, , and excess speeds of sound, u E. Data available in the literature on excess molar enthalpies, , and on excess molar isobaric heat capacities, , of 1-alkanol+linear polyether mixtures indicate that: (i) interactions are mainly of dipolar type, particularly for solutions with longer 1-alkanols; (ii) the ability of the ether to break the alcohol self-association increases with the number of CH2CH2O groups in the oxaalkane. The enthalpies of the alcohol-ether interactions, ΔH OH−O, have been determined. In mixtures with a given polyether, ΔH OH−O increases with the alcohol size. For 1-alkanol+CH3O(CH2CH2O)nCH3 systems, ΔH OH−O decreases for increased n values. Alcohol-ether interactions are stronger in mixtures with linear polyethers than in those with monoethers. data show the existence of free volume effects in solutions including methanol or ethanol. These effects become more important for large n values, which is supported by values of . The Flory model has been used to investigate orientational effects in the systems under study. It is shown that orientational effects are relevant in mixtures with methanol or ethanol, and that the behaviour of the remaining systems is close to that of random mixing. Solutions with 3,6-dioxaoctane slightly differ from this trend and are characterized by weak orientational effects. We have also applied the Flory model to 1-alkanol+PEG-250, or +PEG-350 mixtures, which behave similarly to those including linear polyethers. Orientational effects are much stronger in 1-alkanol+linear monoether systems, and are roughly independent of the mixture components. Results obtained in this work are consistent with those obtained previously when applying the Kirkwood–Buff formalism. [Copyright &y& Elsevier]

Abstract: The Flory model has been applied to linear or cyclic ether+benzene, or +toluene mixtures. In addition, the relative variation of the molar excess enthalpy, , along homologous series of the considered systems, has been discussed taking into account the contributions to from the ether–ether, aromatic–aromatic and ether–aromatic interactions. It has been shown that in CH3(CH2) u−1O(CH2CH2O) v (CH2) u−1CH3 +benzene mixtures, the u increase (v fixed) leads to a weakening of interactions between unlike molecules, and that proximity effects also weaken this type of interactions. In contrast, the v increase (u fixed) or cyclization lead to stronger interactions between unlike molecules. From the application of the model, it is concluded that the random mixing hypothesis may be considered to be valid to a large extent for many of the investigated solutions. Erroneously, strong orientational effects are predicted for 1,3-dioxolane, or 1,4-dioxane+benzene systems, but this has been attributed to the model can not describe asymmetric curves when the mixture compounds show close values for V i (molar volume) and for (reduction parameter for volume). Previous calculations on the basis of the Kirkwood–Buff integrals formalism confirm that the mixture structure is close to random mixing. Flory results on the excess molar volumes have been discussed taking into account the so-called curvature and P* contributions to this excess function. [Copyright &y& Elsevier]

The Flory–Huggins equation has been used to model the equilibrium phase behaviour of a solvent-modified epoxy resin intended for the fabrication of porous components by chemically induced phase separation followed by evacuation of the solvent after curing. Points in composition–temperature space corresponding to a transition from homogeneous to heterogeneous postcuring microstructures have been identified for a variety of solvents using a thermal gradient oven. Assuming this transition to coincide with the cloud-point curve corresponding to the gel point of the resin, the data were used in conjunction with the predictions of the Flory–Huggins equation to estimate the interaction parameter and its temperature dependence for each solvent. Phase diagrams in composition–conversion space were then calculated for a range of curing temperatures. [ABSTRACT FROM AUTHOR]

Se reseñó el libro: "El Conde Lucanor": Don Juan Manuel en su contexto histórico.

Monte Carlo simulations of lattice models of binary (AB) symmetric polymer mixtures (chain lengths N= N= N) in a common good solvent are carried out and the phase diagrams and critical properties of the unmixing transitions are estimated and interpreted in terms of recent theories. Polymers are modeled by self-avoiding walks of length N=16, 32 and 64 on the simple cubic lattice. Data for vacancy concentrations of φ=0.6, 0.8 and 0.85 are analyzed. It is shown that for N=16, φ=0.85 no phase separation occurs, down to the lowest temperature, while for N=32, φ=0.85 still phase separation occurs but no longer is complete. Our results are compatible with a scaling theory based on a 'renormalization' of the Flory-Huggins ϰ-parameter due to 'blob' effects. [ABSTRACT FROM AUTHOR]

This study reanalyzes some elastomeric properties in elongation reported for poly(dimethylsiloxane) (PDMS) networks of high cross-link functionality which had been prepared by using multifunctional siloxane oligomers to end link vinyl-terminated PDMS chains. The extent of reaction of the vinyl end groups P spanned the range of 0.40 to 0.95. These networks had elongation moduli that significantly exceeded the values predicted by the Flory-Erman theory, except at very low values of P. Trends in their stress-strain isotherms, as characterized by the Mooney-Rivlin constants 2 C and the ratio 2 C/C, also appeared to be different from those predicted by theory. Neglected in such standard analyses, however, was the fact that the segments between cross-links along the junction precursor molecules can themselves act as short network chains, contributing to the modulus and giving a strongly bimodal distribution of both network chain lengths and cross-link functionalities. Of particular interest is the apparent change in functionality with extent of reaction and chain length distribution. The results thus obtained do suggest strong dependence of the observed values of the phantom modulus on the network chain-length distribution, particularly at very small values of the ratio of the length of the short chains to the long ones. Calculations based on recognition of these complications can be used to characterize more realistically the deformation of such networks. The results give much better agreement with experiment. Such behavior could be an important characteristic of elastomeric networks in general. Also, a preliminary attempt was made to bridge theory with experiment based on Kloczkowski, Mark, and Erman's recent theory of fluctuations of junctions in regular bimodal networks. The agreement between theory and experiment thus obtained is rather satisfactory and lends further support to assumptions that take into account the possibly bimodal nature of these high-functionality networks. [ABSTRACT FROM AUTHOR]

• Quantified oligomers produced in self-aldol reaction of acetaldehyde using cation exchange resin. • The molecular weight distribution is verified by Flory's statistical method. • The effect of solvent, catalyst weight and temperature are investigated. • The proposed kinetic model explains the trends in production distribution well. Several industrially important liquid phase reactions which involve acetaldehyde as the main reactant are practised in the presence of acidic catalyst. However, under these conditions, acetaldehyde also undergoes oligomerization via self-aldol condensation reactions to form multiple side products thereby reducing the selectivity of the desired product. In this work, we investigate the detailed kinetics of oligomerization over a commonly used commercial cation exchange resin, Amberlyst-15 as catalyst. It is found that, crotonaldehyde and subsequent heavy aldols are formed in the reaction. Molecular weight distribution of the oligomers formed during the reaction is verified with Flory's statistical method. Kinetic studies are performed in an autoclave over a temperature range of 343−363 K. The effect of different parameters such as temperature, concentration, catalyst loading, and catalyst reusability is examined. A kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expression is proposed to explain acetaldehyde oligomerization in the presence of acidic resin. [ABSTRACT FROM AUTHOR]