An ellipsoid-chain model for conjugated polymer solutions

Abstract

We propose an ellipsoid-chain model which may be routinely parameterized to capture large-scale properties of semiflexible, amphiphilic conjugated polymers in various solvent media. The model naturally utilizes the defect locations as pivotal centers connecting adjacent ellipsoids (each currently representing ten monomer units), and a variant umbrella-sampling scheme is employed to construct the potentials of mean force (PMF) for specific solvent media using atomistic dynamics data and simplex optimization. The performances, both efficacy and efficiency, of the model are thoroughly evaluated by comparing the simulation results on long, single-chain (i.e., 300-mer) structures with those from two existing, finer-grained models for a standard conjugated polymer (i.e., poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) or MEH-PPV) in two distinct solvents (i.e., chloroform or toluene) as well as a hybrid, binary-solvent medium (i.e., chloroform/toluene = 1:1 in number density). The coarse-grained Monte Carlo (CGMC) simulation of the ellipsoid-chain model is shown to be the most efficient--about 300 times faster than the coarse-grained molecular dynamics (CGMD) simulation of the finest CG model that employs explicit solvents--in capturing elementary single-chain structures for both single-solvent media, and is a few times faster than the coarse-grained Langevin dynamics (CGLD) simulation of another implicit-solvent polymer model with a slightly greater coarse-graining level than in the CGMD simulation. For the binary-solvent system considered, however, both of the two implicit-solvent schemes (i.e., CGMC and CGLD) fail to capture the effects of conspicuous concentration fluctuations near the polymer-solvent interface, arising from a pronounced coupling between the solvent molecules and different parts of the polymer. Essential physical implications are elaborated on the success as well as the failure of the two implicit-solvent CG schemes under varying solvent conditions. Within the ellipsoid-chain model, the impact of synthesized defects on local segmental ordering as well as bulk chain conformation is also scrutinized, and essential consequences in practical applications discussed. In future perspectives, we remark on strategy that takes advantage of the coordination among various CG models and simulation schemes to warrant computational efficiency and accuracy, with the anticipated capability of simulating larger-scale, many-chain aggregate systems.

Solvent-Regulated Mesoscale Aggregation Properties of Dilute PBTTT-C14 Solutions

“…In contrast, the relatively sluggish dynamics of pBTTT-C 14 chains in chlorobenzene results in more erratic and, hence, looser aggregate packing through isotropic van der Waals forces. Dynamic propertiesbut not static ones, as usually accounted for by the Hansen solubility parametershaving a major influence on the solvation behavior of pBTTT-C 14 chains may be traced back to the sophisticated polymer–solvent interactions in the proximity of the pBTTT-C 14 backbone, akin to what have recently been revealed for fullerene , and conjugated polymer , solutions.…”

Anisotropic Coarse-Grained Model for Conjugated Polymers: Investigations into Solution Morphologies

“…While simultaneous morphological and electronic prediction has historically been obtained via a combination of isotropic CG models, atomistic backmapping, and repeat quantum-chemical calculations, the model described here has the potential to bypass these limitations and dramatically improve the scalability of design space predictions for conjugated materials. While the model has been developed at a lightly CG resolution here, there is the potential to incorporate the mixed isotropic/anisotropic bead description at larger length scales to further aid the exploration of mesoscopic length scales, similar to previous work …”

“…In contrast to quantum-chemical and atomistic molecular dynamics (MD) simulations of conjugated polymers, coarse-grained (CG) and mesoscopic modeling for these materials have been relatively rare. − One reason for this relative scarcity in CG design principles involves the nature of the intermolecular interactions that dictate structure formation in conjugated polymers. Conjugated monomers often contain fused aromatic rings with strongly anisotropic intermolecular interactions, leading to the disk-like stacking of conjugated monomers known as π–π stacking.…”

Aggregation and Solubility of a Model Conjugated Donor–Acceptor Polymer

“…While experimental methods can be applied to assess general aggregation trends, − molecular simulations can reveal the atomistic structure of aggregates that give rise to complex optoelectronic phenomena. We emphasize that in recent studies, atomistic − and coarse-grained − simulations have broached the topic of solution-phase conformations of conjugated polymers. However, an understanding of the thermodynamic contributions to conjugated polymer solubility is still lacking.…”