Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Molecular Dynamics simulation of evaporation processes of fluid bridges confined in slit-like pore
2009
A simple fluid, described by point-like particles interacting via the Lennard-Jones potential, is considered under confinement in a slit geometry between two walls at distance Lz apart for densities inside the vapor-liquid coexistence curve. Equilibrium then requires the coexistence of a liquid "bridge" between the two walls, and vapor in the remaining pore volume. We study this equilibrium for several choices of the wall-fluid interaction (corresponding to the full range from complete wetting to complete drying, for a macroscopically thick film), and consider also the kinetics of state changes in such a system. In particular, we study how this equilibrium is established by diffusion proces…
Calculation of miscibility behavior of multinary polymer blends
1996
A method for the calculation of phase diagrams (tie lines and binodal, spinodal, critical points and their stability) based exclusively on the Gibbs energy of mixing, δG, is presented which does not require the calculation of the derivatives with respect to the composition. The method is demonstrated for ternary mixtures of two homopolymers and the corresponding copolymer, and for quaternary and quinternary blends of five polymers exhibiting a closed miscibility gap. The advantages of the presented method become most obvious in the mathematical description of measured phase diagrams, where complex composition dependencies of the interaction parameter are observed.
Self-assembly of bioelastomeric structures from solutions: Mean-field critical behavior and Flory-Huggins free energy of interactions
1993
Elastic and quasi-elastic light scattering studies were performed on aqueous solutions of poly (Val-Pro-Gly-Gly), a representative synthetic bioelastomer that differs from the previously studied poly (Val-Pro-Gly-Val-Gly) by the deletion of the hydrophobic Val in position four. When the spinodal line was approached from the region of thermodynamic stability, the intensity of light scattered by fluctuations, and the related lifetime and correlation length, were observed to diverge with mean-field critical exponents for both systems. Fitting of the experimental data allowed determining the spinodal and binodal (coexistence) lines that characterize the phase diagrams of the two systems, and it…
Efficient prediction of thermodynamic properties of quadrupolar fluids from simulation of a coarse-grained model: the case of carbon dioxide.
2008
Monte Carlo simulations are presented for a coarse-grained model of real quadrupolar fluids. Molecules are represented by particles interacting with Lennard-Jones forces plus the thermally averaged quadrupole-quadrupole interaction. The properties discussed include the vapor-liquid coexistence curve, the vapor pressure along coexistence, and the surface tension. The full isotherms are also accessible over a wide range of temperatures and densities. It is shown that the critical parameters (critical temperature, density, and pressure) depend almost linearly on a quadrupolar parameter q=Q(*4)T*, where Q* is the reduced quadrupole moment of the molecule and T* the reduced temperature. The mode…
Liquid–liquid equilibria of 4-methyl-2-pentanone+1-propanol or 2-propanol+water ternary systems: Measurements and correlation at different temperatur…
2014
Abstract In this work, experimental liquid–liquid equilibria data of the systems 4-methyl-2-pentanone + 1-propanol + water and 4-methyl-2-pentanone + 2-propanol + water are presented. The liquid–liquid equilibria of both systems have been measured at 283.2 and 323.2 K. The NRTL and UNIQUAC models were successfully applied to fit the data for both ternary systems. The binodal lines were compared to the values predicted by the UNIFAC-LLE and UNIFAC models. Moreover, the solvent capability of 4-methyl-2-pentanone was checked in order to separate the azeotropic mixtures formed by propanol's and water.
Measurements and correlation of liquid–liquid equilibria of 4-methyl-2-pentanone+ethanol+water and 4-methyl-2-pentanone+n-butanol+water ternary syste…
2012
Abstract In this work, experimental liquid–liquid equilibria data of the systems 4-methyl-2-pentanone + ethanol + water and 4-methyl-2-pentanone + n-butanol + water are presented. The liquid–liquid equilibria of both systems have been measured between 283.2 and 323.2 K. The NRTL and UNIQUAC models were applied to fit the data for both ternary systems. The interaction parameters obtained from both models successfully correlated the equilibrium compositions. The binodal lines were compared to the values predicted by the UNIFAC-LLE and UNIFAC models. Moreover, the solvent capability of 4-methyl-2-pentanone was checked in order to separate these azeotropic mixtures alcohol + water.
Polymer Incompatibility Caused by Different Molecular Architectures: Modeling via Chain Connectivity and Conformational Relaxation
2009
The calculation of phase diagrams for blends of linear and branched polymers made up of identical monomeric units is modeled using an approach that subdivides the mixing process into two steps: i) contact formation between the different components, keeping their chain conformations and the volume of the system constant; and, ii) relaxation of the macromolecules into their equilibrium state by molecular rearrangements. It is assumed that step (ii) causes shape-induced polymer incompatibility and that the degree of branching can be quantified in terms of the volumes the isolated coils of the branched polymer occupy in relation to the volume the linear product with the same molecular weight oc…
Demixing of unsheared and sheared solutions of polystyrene in tert-butylacetate and the pressure influence on their flow behaviour
1979
For the system tert-butyl acetate/polystyrene (M= 670000) the phase separation behaviour (upper critical solution temperatures, upper critical solution pressures) is investigated by means of visual and turbidimetric cloud-point measurements and by viscometry. For near-critical concentrations the visually determined cloud-points are found at higher, for low concentrations at lower temperatures as compared with the turbidimetrically determined binodal temperature,Tbin Plots of the invers of the turbidity measured atTbin as a function of the polymer concentration,w2, yield a minimum from which the critical composition can be determined. The viscometrically obtained demixing points (break-down …
Saving time when measuring BET isotherms.
2007
The measurement of adsorption isotherms and the detn. of surface properties of a solid by means of the BET equation usually takes a lot of time as it involves measurement of several dynamic adsorption curves each at a given gas pressure. Two different timesaving approaches are suggested: (a) the beginning of a single dynamic curve is considered and (b) the beginnings of a no. of different dynamic curves is considered. Approach (a) is less time consuming than approach (b), where approach (b) yields more accurate ests. of the BET-parameters. A discussion is given of the possibilities of using the time saving procedure of Jaentti for the two approaches. [on SciFinder (R)]
Hybrid Quantum Mechanics/Molecular Mechanics Simulations with Two-Dimensional Interpolated Corrections: Application to Enzymatic Processes
2006
Hybrid quantum mechanics/molecular mechanics (QM/MM) techniques are widely used to study chemical reactions in large systems. Because of the computational cost associated with the high dimensionality of these systems, the quantum description is usually restricted to low-level methods, such as semiempirical Hamiltonians. In some cases, the description obtained at this computational level is quite poor and corrections must be considered. We here propose a simple but efficient way to include higher-level corrections to be used in potential energy surface explorations and in the calculation of potentials of mean force. We evaluate a correction energy term as the difference between a high-level …