Search results for "Entropy of mixing"
showing 10 items of 18 documents
Thermodynamic Interaction Parameters for the System Water/NMMO Hydrate
2008
Vapor pressures of water were measured for aqueous solutions of N-methyl-morpholine N-oxide (NMMO) at 80, 90 and 100 degrees C. The Flory-Huggins interaction parameters, chi, calculated from these data as a function of phi, the volume fraction of NMMO, are negative at all concentrations; at low phi, they decrease by more than a factor of 2 as T is raised, whereas they remain almost unchanged as phi approaches unity. Accordingly, the heat of mixing is pronouncedly endothermal at low NMMO concentrations but close to athermal at low water content. The composition dependence of chi can be equally well described by the Redlich-Kister equation and by an approach subdividing the mixing process int…
Enthalpies of mixing of some nitriles aqueous solutions with dodecylsurfactants micellar solutions
1988
The enthalpies of mixing of some n-nitriles (from acetonitrile to valeronitrile) aqueous solutions with dodecyltzimethylammonium bromide, sodium dodecylsulfate and dodecyltzimethylammonium oxide micellar solutions were determined. The measurements were performed by systematically changing the surfactant concentration at a given solute concentration. The experimental enthalpies were rationalized in terms of the standard enthalpy of transfer of solute from the aqueous to the micellar phase and of the distribution constant between the two phase. Information on the effect of the nature of the surfactant on the standard thermodynamic quantities of transfer(ΔG t o , ΔH t o , TΔS t o ) is reported…
Kristallisations- und schmelzverhalten von copolymeren aus 3,3-bis(chlormethyl)oxetan und ß-propiolacton
1974
Einkristalle von Copolymeren aus 3,3-Bis(chlormethyl)oxetan und s-Propiolacton wurden bezuglich Schmelzverhalten, Schmelzenthalpie, Dichte und Langperiode untersucht. Aus der Messung der Schmelzenthalpie und der Dichte berechnen sich Kristallisationsgrade von 50—60% in guter Ubereinstimmung mit einem Modell, welches den Ausschlus der aus s-Propiolacton (PL) entstandenen Grundbausteine von dem aus Sequenzen der 3,3-Bis(chlormethyl)oxetan (BCMO-)Einheiten aufgebauten Gitter verlangt. Im Vergleich zu reinem Poly-BCMO wird die Dicke der Copolymereinkristalle nur wenig durch Anderung der Kristallisationstemperatur beEinflust. Wegen des blockartigen Aufbaus der Copolymeren bestimmt die mittlere S…
Thermodynamics of Phase Behavior in PEO/P(EO-b-DMS) Homopolymer and Block Co-Oligomer Mixtures under Pressure
2003
The cloud-point temperatures (T-cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)-block-polydimethylsiloxane (P(EO-b-DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130degrees), pressures (1 to 800 bar), and compositions (10-40 wt.-% PEO). The system phase separates upon cooling and T-cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T-phi plane (where…
Latent Heat of Spontaneous-Curvature-Induced Lamellar-to-Microemulsion Transitions
1995
Using differential scanning microcalorimetry we examine the latent heat of the temperature-induced structural transition from a lamellar to a microemulsion phase in a H2O/n-octane/C12E5 (n-dodecyl pentanethyleneglycol ether) system. The associated latent heat increases strongly with surfactant concentration yielding heat changes up to 1kB T per surfactant molecule. These large values are quantitatively described by an interfacial model which takes into account the temperature dependence of the spontaneous curvature. The model explains our data points without considering contributions to the free energy by thermal fluctuations, entropy of mixing, undulations of the lamellae and renormalizati…
Cylindrical confinement of solutions containing semiflexible macromolecules: surface-induced nematic order versus phase separation
2021
Solutions of semiflexible polymers confined in cylindrical pores with repulsive walls are studied by Molecular Dynamics simulations for a wide range of polymer concentrations. Both the case where both lengths are of the same order and the case when the persistence length by far exceeds the contour length are considered, and the enhancement of nematic order along the cylinder axis is characterized. With increasing density the character of the surface effect changes from depletion to the formation of a layered structure. For binary 50 : 50 mixtures of the two types of polymers an interplay between surface enrichment of the stiffer component and the isotropic-nematic transition is found, and a…
Configurational entropy of microemulsions : The fundamental length scale
1993
Phenomenological models have been quite successful in characterizing both the various complex phases and the corresponding phase diagrams of microemulsions. In some approaches, e.g., the random mixing model (RMM), the lattice parameter is of the order of the dimension of an oil or water domain and has been used as a length scale for computing a configurational entropy, the so‐called entropy of mixing, of the microemulsion. In the central and material section of this paper (Sec. III), we show that the fundamental length scale for the calculation of the entropy of mixing is of the order of the cube root of the volume per molecule—orders of magnitude smaller than the dimension of such a domain…
Phase diagrams calculated for flowing polymer solutions: spinodal and three phase conditions
1998
Spinodal lines and critical points (CPs) are calculated for flowing solutions of polystyrene in trans-decalin. Three types of CPs can be distinguished: The first consists of stable CPs (ordinary critical line) and originates from the CP of the quiescent system. The other two CPs are bound to shear. Additional stable CPs (extraordinary critical line) result for higher polymer concentrations and unstable CPs for intermediate concentrations. Ordinary and unstable critical line merge in a heterogeneous double CP. The coexistence of three phases in the flowing system (eulytic points) comes to an end as two of them merge upon an increase in shear rate at a critical end point.
Phase separation in multi-component mixtures: the four-component case
2002
Abstract Calculation of ternary phase diagrams for several mixtures formed by two salts and a neutral component is presented here. The phase diagrams are obtained by inspection of the shape of the Gibbs free energy of mixing surface (Gmix) as a function of the composition at constant temperature and pressure. The Gmix surface is calculated by the mean spherical approximation (MSA). The model for the mixtures is represented by hard spheres, with the charged components interacting via a Coulomb potential. The results are interpreted in terms of a thermodynamic analysis of the contributions to the Gibbs free energy of mixing, i.e., the configurational energy, the volume and the entropy of mixi…
A thermodynamic approach to study hydrogen-bonding interactions in solvent/solvent/polymer ternary systems
2007
Abstract A thermodynamic approach based on both the classical Flory–Huggins (FH) formalism and the association equilibria (AE) theory has been developed to study the solubility properties of a system formed by a proton-donor solvent (A), a proton-acceptor solvent (B) and a proton-acceptor polymer (C). The miscibility of this ternary system is attained by competitive specific interactions via hydrogen-bonding established between the hydroxyl and carbonyl interacting groups of either solvent–solvent (AB) or solvent–polymer (AC) system components. The binary AB and AC specific interactions and their dependence with the system composition as well as with the extent of the association equilibriu…