Mesoscale model parameters from molecular cluster calculations

Abstract

We present an efficient, systematic, and universal method to estimate the interaction parameters used in mesoscale simulation methods such as dissipative particle dynamics and self-consistent field methods from molecular cluster calculations. The method is based on a generalized Flory-Huggins model in which molecules, or fragments thereof, are in contact with their van der Waals surface. We sample the density of states of molecular clusters in the space spanned by the coarse-grained degrees of freedom. From here, we calculate the sum over states and free energy of the cluster at a temperature of interest by histogram reweighting. The method allows to calculate the energy and entropy contributions to the cluster free energy explicitly. For two components, we then obtain the excess free energy of mixing and the Flory-Huggins chi-parameter, and their energetic and entropic contributions. We present two applications of the method: a simple liquid mixture of hexane and nitrobenzene, and a series of polymer blends. In the case of hexane/nitrobenzene, we compare to alternative simulation methods; here we find that the energy of mixing alone is too high to explain the critical point. By including the excess entropy of mixing, however, the predicted phase behavior is in reasonable agreement with experiment. The tendency of calculations based on average energy alone to overestimate the chi-parameter is also apparent in the polymer blend calculations.

Perspective: Dissipative particle dynamics

“…This can be accommodated within the MDPD approach. Akkermans [250] presents a first principles coarse-graining method that allows to calculate the excess free energy of mixing and Flory-Huggins χ-parameter. A related effort is given by Goel et al [251].…”

Highly Responsive and Thermally Reliable Near‐Infrared Organic Photodiodes Utilizing Naphthalocyanine Molecules Tuned with Axial Ligands

“…The module Blends was used to predict the mixing energy and the interaction parameters (χ) based on the Flory-Huggins theory. [27,28] The calculated χ parameters were found to increase with the reduction in the chain length. For instance, the SiNc-C3, -C4, and -C6 exhibit χ values of −15.3, −23.5, and −26.0, respectively.…”

Parameterization of a mesoscopic model for the self-assembly of linear sodium alkyl sulfates

“…For all other non-bonded parameters, the range investigated has been chosen in agreement with typical values in the literature. [60][61][62][63] The pertinent χ parameter between hydrocarbon (per carbon atom) and water χ carbon-water is reported to be between 1.6 and 2.0, determined by matching the solubility data of oil in water and vice versa. 49,64 In the present study, repulsion parameter between water and tail beads a WT , varied from 90 to 104, was derived from χ WT = 2.7 to 6.0 (χ carbon-water = 0.9-2.0), corresponding to three water molecules per W bead or three carbon atoms per T bead.…”