Search results for "Gibbs"

Excess free energy, enthalpy and entropy of surfactant-surfactant mixed micelle formation

1996

Enthalpies of dilution and osmotic coefficients of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO) mixtures in water were determined at 298 and 310 K, respectively. From the enthalpies of dilution, the apparent and then the partial molar relative enthalpies of the surfactant mixtures were calculated. From the osmotic coefficients, calculated at 298 K, the non-ideal free energies were derived. The latter were combined with the partial molar relative enthalpies to obtain the non-ideal entropies. From the apparent molar properties, using a previously reported approach, the excess thermodynamic properties for the surfactant-surfactant mixed micelle formation in water were evaluate…

Interfacial tension between polymer-containing liquids - Predictability and influences of additives

1999

The first part of the contribution deals with the interfacial tension, σ, of phase-separated polymer solutions in single or mixed solvents and of binary polymer blends as a function of the relative distance to the critical temperature of the system, special attention being paid to the possibilities of theoretical prediction. Two methods are discussed in more detail. One is based on a realistic description of the Gibbs energy of mixing as a function of composition, the second correlates σ with the length of the measured tie line. The second part is devoted to another aspect, namely the effects of additives on the interfacial tension between the coexisting phases of demixed polymer solutions …

Quick and reliable routes to phase diagrams for polyethersulfone and polysulfone membrane formation

2000

Phase diagrams were measured and calculated for the ternary membrane forming systems DMF/water/polysulfone and DMF/water/polyethersulfone at different temperatures. Customary experiments yielded cloud point curves, tie lines, and critical compositions. The theoretical computation starts from the Flory-Huggins theory and employs binary interaction parameters g ij that vary with the composition. This information was mainly obtained by means of Headspace-Gas Chromatography (HSGC, yielding the partial pressures of the volatile components); these data were complemented by light scattering and swelling experiments. The calculation of binodals, spinodals, tie lines, and critical points avoids the …

Shear Effects on the Phase Diagrams of Solutions of Highly Incompatible Polymers in a Common Solvent. 1. Equilibrium Behavior and Rheological Propert…

1997

Phase diagrams (cloud points, tie lines, critical compositions) and viscosities of homogeneous solutions were determined at temperatures ranging from 20 to 100 °C for three representatives of the ternary system cyclohexanone/polystyrene/poly(n-butyl methacrylate) [CHO/PS/PBMA] in preparation of a study on shear influences. An only moderate increase of the two-phase region observed upon heating (LCST behavior) witnesses little heat effects upon mixing. Tie lines which are nearly parallel to the PS/PBMA edge of the Gibbs phase triangle indicate comparable solvent quality of CHO for both polymers. The quantitative mathematical description of the equilibrium behavior-required for a theoretical …

Pressure dependence in the methyl vinyl ketone + OH and methacrolein + OH oxidation reactions: an electronic structure study.

2005

High-level electronic structure calculations were carried out for the study of the reaction pathways in the OH-initiated oxidations of methyl vinyl ketone (MVK) and methacrolein (MACR). For the two conformers of MVK (called synperiplanar and antiperiplanar), the addition channels of OH to the terminal and central carbon atom of the double bond dominate the overall rate constant, whereas the abstraction of the methyl hydrogen atoms has no significant kinetic role. In the case of MACR, only the antiperiplanar conformer is important in its reactivity. In addition, the lower Gibbs free energy barrier for MACR corresponds to the aldehydic hydrogen abstraction reaction, which will be somewhat mor…

Understanding the domino reactions of alkyne-tethered N-tosylhydrazones yielding fused polycyclic pyrazoles. An MEDT study

2019

Abstract The domino reactions of alkyne-tethered N-mesylhydrazones yielding fused polycyclic pyrazoles have been studied within the Molecular Electron Density Theory (MEDT). Analysis of the Gibbs free energies indicates that the more favourable reactive path is the one in which the elimination of mesylate anion takes place before the intramolecular [3 + 2] cycloaddition (IM32CA) reaction, which corresponds with the rate-determining step of these domino processes. ELF topological analysis of the bond formation along the IM32CA reaction indicates that in spite of the high activation energy associated to this intramolecular reaction, it shows a pmr-type mechanism characterised by the presence …

Modelling the hydrogen-bonding interactions in a copolymer/biodegradable homopolymer blend through excess functions

2008

A recent theoretical approach based on the coupling of both the Flory-Huggins (FH) and the Association Equilibria thermodynamic (AET) theories was modified and adapted to study the miscibility properties of a multi- component system formed by two polymers (a proton-donor and a proton-acceptor) and a proton-acceptor solvent, named copolymer(A)/solvent(B)/polymer(C). Compatibility between polymers was mainly attained by hydrogen- bonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the car- bonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self- association of PSVPh and specific interacti…

Controlling the wetting properties of the Asakura-Oosawa model and applications to spherical confinement.

2012

We demonstrate for the Asakura-Oosawa model and an extension of this model that uses continuous rather than hard potentials, how wetting properties at walls can be easily controlled. By increasing the interaction range of the repulsive wall potential acting on the colloids (while keeping the polymer-wall interactions constant) polymers begin to substitute colloids at walls and the system can be driven from complete wetting of colloids via partial wetting to complete wetting of polymers. As an application, we discuss the morphology and wetting behavior of colloid-polymer mixtures in spherical confinement. We apply the recently developed 'ensemble switch method' where the Hamiltonian is exten…

1988

Phase diagrams were calculated for flowing solutions of polystyrene in trans-decahydronaphthalene assuming that the energy (Es) stored in the sheared state has to be added to the Gibbs energy of mixing; Es is computed from viscometric data (flow curves). The resulting phase diagrams exhibit two maxima in most of the cases instead of only one for the stagnant solutions. A comparison with experimental data (Part 1) shows that the calculated demixing behaviour agrees well for moderate shear rates and concentrations of the polymer. Deviations in the semidilute region, particularly for higher values, are a consequence of the fact that so far no reliable theoretical relation has been given for th…

1988

The unperturbed dimensions parameter KΘ is one of the most important characteristics of a polymer chain. For binary systems (polymer/solvent) and mostly for ternary systems (polymer/solvent(1)/solvent(2)) the KΘ values show large discrepancies with respect to those under thetaconditions in a single solvent. These discrepancies can be explained by considering that the interaction parameter χ (and consequently the coil dimensions or the number of intramolecular contacts between polymer segments) changes with molecular weight M. Assuming this dependency, a modified Stockmayer-Fixman equation is proposed from which a unique value of KΘ for a given polymer, independent of M, is obtained. The use…