Search results for "Nod"
showing 10 items of 4007 documents
The droplet evaporation/condensation transition in a finite volume
2003
A fluid in the NVT ensemble at T less than the critical temperature T_c and rho = N/V somewhat in excess of rho_coex (density of the saturated gas in the gas-liquid transition) is considered. For V->infinity, a macroscopic liquid droplet coexists with surrounding saturated gas according to the lever rule. For finite V, droplets can only exist if they exceed a minimum size. A (rounded) first order transition of the system occurs when the droplet evaporates into the supersaturated gas.Simulation evidence for this transition is given for a Lennard-Jones model and interpreted by a phenomenological theory. At the transition, the chemical potential difference mu_t-mu_coex scales like L^(-d/(d+…
Sedimentation of dissolved macromolecules in the vicinity of the consolute point 1. Strictly binary systems and kinetic considerations
1986
This paper analyzes the effect of gravity on polymer solutions near the consolute point. Calculations are carried out for monodisperse polystyrene in cyclohexane using the Flory-Huggins expression with a concentration-dependent interaction parameter for the free energy of mixing. Depending on molecular weight and distance to the demixing temperature, the influence of gravity leads to non-negligible gradients of the volume fraction in the one-phase region as well as in the two-phase region. In particular, the effect of gravity on the measurement of the coexistence curve in a finite sample is calculated explicitly.
Calculation of phase diagrams not requiring the derivatives of the Gibbs energy demonstrated for a mixture of two homopolymers with the corresponding…
1995
A method is presented which allows the calculation of phase diagrams (spinodal, binodal and tie lines) on the basis of the Gibbs energy of mixing ΔG. No derivatives of ΔG with respect to the composition variables are required. This method is particularly useful in cases where the composition dependence of ΔG is very complex and no analytical representation of the derivatives can be given. The method is applied to a ternary mixture of two homopolymers with a copolymer consisting of the same monomers. The sequence distribution of the copolymer is kept constant between random and purely alternating, and phase diagrams are calculated for different chemical compositions of the copolymer. The com…
Thermodynamics of a polymer blend solution system studied by gel permeation chromatography and viscosity
1999
Binary and ternary interaction parameters and their derivatives have been calculated with the Flory-Huggins formalism developed for a ternary polymer system. The equilibrium compositions of the ternary system tetrahydrofuran/polybutadiene/polystyrene that forms two phases in equilibrium at 25°C have been used to solve the binodal equations. With this set of parameters, the viscosimetric interaction parameters have been computed. For the sake of comparison, the experimental viscosimetric parameter has been determined from intrinsic viscosity data of a polymer (3) in a "binary solvent" (solvent + polymer (2)). It has been clearly shown that composition-dependent parameters are necessary to re…
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…
Demixing time and temperature influence on porosity and interconnection of PLLA scaffolds prepared via TIPS
2009
Scaffolds suitable for tissue engineering applications were prepared by Thermally Induced Phase Separation (TIPS) starting from a ternary solution PLLA/ dioxane/water. The experimental protocol consisted of three consecutive steps, a first quench from the homogeneous solution to an appropriate demixing temperature (within the binodal region), a liquid-liquid demixing stage for a given time and a final quench from the demixing temperature to a low temperature (within the spinodal region). A large variety of morphologies, in terms of average pore size and interconnection were obtained upon modifying the demixing time and temperature, owing to the interplay of nucleation and growth processes d…
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.