Application of molecular simulation to derive phase diagrams of binary mixtures

Abstract

The miscibility behavior of three binary mixtures, solvent with solvent, polymer with solvent, and polymer with polymer, was studied by use of a combination of the Flory-Huggins theory and molecular simulation techniques. Fundamental parameters in the Flory-Huggins theory, including the heat of mixing associated with pairwise interactions (Awn) and the number of possible interaction partners, i.e., coordination number, z, are calculated from molecular simulations. The pair energies (wn, w22, wu) are obtained by averaging a large number of configurations generated by a Monte Carlo approach which includes the constraints associated with excluded volume. The temperature dependence of the interaction parameter x is obtained with the formalism developed in this study. In all cases, the calculated upper critical solution temperatures compare favorably with experimental values. This approach provides an opportunity to test the Flory-Huggins theory for a number of model binary systems and to characterize their miscibility behavior. This combined approach also facilitates study of the thermodynamic behavior of a binary mixture without possessing specific knowledge or experimental data of the system under investigation.

A Computer Simulation Study of the Mesoscopic Structure of the Polyelectrolyte Membrane Nafion

“…22,23 Several available methods for evaluating the χ-parameter for polymer-polymer, polymer-solvent, and solvent-solvent pairs in blend systems have already been proposed using an atomistic simulation based on the cohesive energy or the heat of mixing theory. [24][25][26][27][28][29] According to the synthesis process of the Nafion membrane in the case of a casting procedure, 13,30 the structure of the hydrated Nafion membrane seems to be spontaneously formed from solution in an alcohol and water mixture, in a way similar to the microphase separation of polymer mixture systems. Therefore, it is expected to predict the structure of the hydrated Nafion membranes by a mesoscopic simulation when we use appropriate χ-parameters for the Nafion polymer and water.…”

Molecular dynamics simulation study of compatibility for the polyvinylmethylether/polystyrene mixture

“…Therefore, they are less affected by the choice of potential parameters. We have verified that alternative estimations of χ based in the direct evaluation of the intermolecular energy between a pairs of units averaged over a statistical sample generated through Monte Carlo simulations [11] (as incorporated in the MS module "Blends") seem to be considerably less precise in the present mixture, depending largely on small details in the forcefield definitions. Similar large dependence on the potential details are found when χ is obtained from estimations of the cohesive energy density, or the solubility parameter [12], which can be directly evaluated form the MD simulations using an "Analysis" tool incorporated in the "Amorphous Cell" module.…”

“…Table 2 shows the results obtained with the MS module "Blends" based in the method for the direct evaluation of the intermolecular energy between a pairs of units described in Ref. [11], according to the MS module "Blends". It can be observed that 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 …”

Dissipative particle dynamics simulation of wettability alternation phenomena in the chemical flooding process

“…Dodecane, water and solid are represented by one particle denoted by "O", "W" and "S", respectively. The interaction parameters between two kinds of DPD particle can be evaluated according to the mixing energy and Flory-Huggins interaction parameters, which can be obtained by Blend simulation based on Monte Carlo methods [22]. The calculated conservation parameters a i j are given in Table 1(temperature K B T is set at 1.2 and particle density is set at 3).…”