A coarse-grained (CG) model and Langevin dynamics scheme are proposed to investigate the material properties in dilute solution of a model semiconducting conjugated polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). While the intra- and intermolecular potentials for the CG particle (currently, a monomer unit) were determined from the molecular dynamics (MD) simulation of a united atomistic model, fluctuation-dissipation forces arising from the treatment of a solvent field were self-consistently constructed from the measured particle diffusivity in a given solvent (i.e., chloroform or toluene) through the atomistic MD simulation. It is shown that the resultant Langevin dynamics simulation, which is substantially more efficient than the counterpart MD simulation of the same CG model, is able to capture the dynamic (such as center-of-mass diffusivity) as well as the structural (such as radius of gyration) features of the investigated polymer solutions. Essential material properties that can now be directly studied include the following: Scaling exponents for estimating the exact solvent qualities were, for the first time, determined for the two solvent systems investigated; the persistence length obtained was also noted to be in excellent agreement with early experimental estimations. Preliminary observations on the supramolecular aggregation properties were in good agreement with the general observations from a wide range of recent experiments, and shed light on the essential impact of solvent quality on the supramolecular aggregation structures.

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.

The van der Waals (vdW) potentials governing macroscopic objects have long been formulated in the context of classical theories, such as Hamaker's microscopic theory and Lifshitz's continuum theory. This work addresses the possibility of constructing the vdW interaction potentials of nanoparticle species using multiscale simulation schemes. Amorphous silica nanoparticles were considered as a benchmark example for which a series of (SiO(2))(n) (n being an integer) has been systematically surveyed as the potential candidates of the packing units that reproduce known bulk material properties in atomistic molecular dynamics simulations. This strategy led to the identification of spherical Si(6)O(12) molecules, later utilized as the elementary coarse-grained (CG) particles to compute the pair interaction potentials of silica nanoparticles ranging from 0.62 to 100 nm in diameter. The model nanoparticles so built may, in turn, serve as the children CG particles to construct nanoparticles assuming arbitrary sizes and shapes. Major observations are as follows. The pair interaction potentials for all the investigated spherical silica nanoparticles can be cast into a semiempirical, generalized Lennard-Jones 2alpha-alpha potential (alpha being a size-dependent, large integral number). In its reduced form, we discuss the implied universalities for the vdW potentials governing a certain range of amorphous nanoparticle species as well as how thermodynamic transferability can be fulfilled automatically. In view of future applications with colloidal suspensions, we briefly evaluated the vdW potential in the presence of a "screening" medium mimicking the effects of electrical double layers or grafting materials atop the nanoparticle core. The general observations shed new light on strategies to attain a microscopic control over interparticle attractions. In future perspectives, the proposed multiscale computation scheme shall help bridge the current gap between the modeling of polymer chains and macroscopic objects by introducing molecular models coarse-grained at a similar level so that the interactions between these two can be treated in a consistent and faithful way.

Innovation in modern material science exploiting conducting conjugated polymers imperatively demands fundamental knowledge of single-chain conformations from solution to the quenching state. This urgent goal, however, poses a stringent challenge to existing simulation schemes, especially when the polymer of interest possesses simultaneously a high molecular weight and anisotropic local interaction forces, such as hydrogen-bond (HB) and pi-pi interactions. Considering a standard case with polyaniline emeraldine base (PANI-EB), widely used as the conducting layer in polymer-based optoelectronic devices, this paper introduces how the current difficulty may be circumvented by using a multiscale simulation scheme that takes advantage of a systematic mapping and back-mapping between atomistic molecular dynamics (AMD), coarse-grained molecular dynamics, and coarse-grained Langevin dynamics (CGLD). Whereas a self-consistent CGLD simulation greatly facilitates reaching representative long-chain conformations in specific solvents, the back-mapped AMD simulation permits scrutiny into the effects of localized HB and pi-pi interactions on quenched chain morphologies. The basic idea behind this multiphase simulation scheme for conducting conjugated polymers has been consolidated by the central observation for PANI-EB: whereas segmental van der Waals interactions dominate fundamental single-chain properties in solution (i.e., persistence length, solvent quality, and chain diffusivity), the anisotropic HB and pi-pi interactions accordingly "trap" the quenched chain to a morphology closely mimicking that in the prior solution state-the first microscopic evidence of the so-called "memory effect." Notably, the central features disclosed for PANI-EB as well as the multiscale simulation strategy proposed for tracking single-chain conformations from solution to the quenching state are asserted to hold for typical conducting conjugated polymers that possess, ubiquitously, a semiflexible backbone and localized interaction forces.