Hybrid Solvents Incubated π−π Stacking in Quenched Conjugated Polymer Resolved by Multiscale Computation

Abstract

Multiscale computations were utilized to resolve the detailed solvent-polymer interactions in binary (aliphatic/aromatic) solvent media of a standard amphiphilic conjugated polymer, poly(2-methoxy-5-(2 0 -ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), revealing an unequivocal pathway specific solvents or hybrid solvents impact the nanomorphology in the eventual quenching state. The significant finding is that, through sophisticatedly compromised, local-phase solvent particle distribution encompassing the polymer chain, certain solvent compositions (i.e., chloroform/chlorobenzene = 2:1 and chloroform/toluene = 1:1 in number density) were noted to bolster exceptional, highly extended chain conformations in solution, which in turn greatly facilitate the incubation of ordered π-π stacking upon solvent evacuation via a relatively regular chain folding along the pivotal tetrahedral defects. Overall, the simulation helps clarify a long-standing ambiguity as to the molecular effects of specific solvents and, in particular, unveils previously unnoticed physics underlying the promising features of hybrid solvents in casting polymer thin films, as evidenced by recent experiments.

An ellipsoid-chain model for conjugated polymer solutions

“…The following are some details of the simulations: The explicit-solvent CGMD simulation utilized the NPT ensemble at T = 298 K and P = 1 atm; details can be found in an early work. 4 For the CGLD and CGMC In all cases, an ensemble average based on 100 independent chains was utilized to create the plot, and the symbols represent CGMD (triangles), CGLD (squares), and CGMC (circles). For clarity, the curves have been shifted in the x-axis direction by varying degree.…”

“…Several peculiar features for binary-solvent system based on this CG polymer model have previously been unveiled. 4 Of particular interest was the first revelation of coupling solvent interactions with different parts of the polymer, leading to crystal-like or layered structure of the solvent molecules in the proximity to the polymer chain. As usual, however, the corresponding CGMD simulation is very expensive, and hence, only single chains of moderate chain lengths may be investigated.…”

“…Considering this particular solvent composition (i.e., chloroform/toluene = 1:1 in number density) was, in fact, motivated by an early finding that the CGMD simulation displayed, among all other compositions investigated, the most prominent deviations from what might be expected using simple mixing rule of the results for the two single-solvent systems. 4 In that case, there seemed to be a prominent coupling between the two solvent species when interacting with different parts of the polymer chain. From the predicted solvent quality exponents as shown in Fig.…”

Nanomorphologies in Conjugated Polymer Solutions and Films for Application in Optoelectronics, Resolved by Multiscale Computation

“…An important advantage of the above choice is, in fact, that a simple mixing rule may be adopted to describe the pair potentials for unlike CG particles, thus saving a lot of computational effort. Justifications of such simplified treatment for the simulation systems under investigation have been discussed in earlier work (Lee et al 2009;Lee et al 2011). For the polymer model depicted in Figure 3, which represents the "finest" CG polymer model in this review article, the two side-chain groups are treated as independent CG particles so as to discriminate the chemical affinities of various types of solvent molecules with respect to different parts of the polymer chain.…”

“…The polymer model depicted in Figure 3 and the corresponding CGMD simulation are especially relevant to resolving the detailed polymer-solvent interactions in various solvent or hybrid-solvent systems; more details can be found in an early work (Lee et al, 2011). In the literature, some confusion prevailed regarding the "solvent quality" for an amphiphilic conjugated polymer like MEH-PPV, and further clarification on this fundamental issue for polymer solution would be possible if a better understanding into such interactions can be gained in an unequivocal way.…”