Structural properties of polystyrene oligomers in different environments: a molecular dynamics study

Abstract

We have performed detailed molecular dynamics simulations to investigate the effects of solvation and confinement on the structure of polystyrene (PS) oligomers in four different environments, melt, concentrated solution, dilute solution and confined concentrated solution at 450 K and 1 bar, respectively. Local packing of the monomers and the solvent (toluene, good solvent) molecules were monitored by means of radial distribution functions (RDFs). We have also investigated bond, angle, and dihedral angle distributions of the monomers. End-to-end distances, radii of gyration and persistence lengths were calculated to characterize the static properties. The chain in the dilute solution was found to exhibit more stretched conformations. Dilution effect of the solvent was observed in the RDFs between the monomer centers. Only slight conformational changes in the polymers were observed by solvation. The effect of confinement was mainly seen in the density profiles, which showed an oscillatory behavior in the confined system.

Modeling of Polystyrene under Confinement: Exploring the Limits of Iterative Boltzmann Inversion

“…We have reported the methodological details and results of the atomistic simulations earlier. 1,3 In short, the reference system is composed of 48 PS chains of 15 monomers with a ratio of meso to racemic dyads of 1:1 solvated in 745 toluene molecules confined between opposing graphene surfaces (each composed of two sheets) separated by 4.51 nm in z-direction. The allatom model for PS was taken from earlier studies.…”

“…Besides, the differences in the local and global structure and the dynamics of the chains in different confinement levels are also addressed based on the results of the corresponding reference atomistic simulations. In order to make an appropriate comparison, previous simulation results of an unconfined (bulk) system (of the same concentration) 1,3 are also presented. To the best of our knowledge, this is the first computational study that reports the structural behavior of polymers in the vicinity of surfaces in a concentrated solution rather than in a melt.…”

“…3,19 As a consequence, there are only few reports on coarse-graining of polymers in close contact with surfaces. 19−22 Moreover, considering the density fluctuations near surfaces in confined systems, 1,20,23,24 it is even more challenging to develop a CG model by means of a structure based coarse-graining technique such as IBI as the system is locally in different state points. 3 In the previous publication, 3 we briefly addressed some of the challenges faced during our implementation of the IBI method on coarsegraining of the confined concentrated PS solution.…”

“…1 An important application of polymers is their use as lubricants or adhesives, 2 which generates the need to improve our understanding of the structure, thermodynamics, and rheology of polymers near solid surfaces. 1 Molecular dynamics simulations are complementary to experiments and are a great tool to study structural and dynamic properties of polymers. Modeling polymers, however, is a challenging task due to the enormous variety of length and time scales involved in the description of their structural and dynamic properties.…”

“…8 According to Milano et al the basic idea goes back to Soper,9 which was adapted and named iterative Boltzmann inversion (IBI) by Reith et al 10 IBI reproduces the structure of the underlying atomistic system by means of an iterative optimization scheme through which the effective potentials between superatoms (CG sites) are obtained. 3 It is motivated by Henderson's theorem 11 which states that there is a unique mapping between the radial distribution function (g(r)) and the intermolecular potential (V) for simple pairwise additive and spherically symmetric potentials at a given thermodynamic state point: 12 = − V k T g r ln( ( )) B (1) eq 1 is actually a potential of mean force and it equals the potential energy only in the limit of infinite dilution. 10 According to Chan et al 12 this is only valid for particles or molecules with a single interaction site rather than molecules with multiple interaction sites (like polymers) since the relation does not account for orientation correlations.…”