Computer simulation of bottle-brush polymers with flexible backbone: Good solvent versus theta solvent conditions

Theodorakis, Panagiotis E.; Hsu, Hsiao-Ping; Paul, Wolfgang; Binder, Kurt

doi:doi:10.1063/1.3656072

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Limit of validity of Ostwald's rule of stages in a statistical mechanical model of crystallization

We have only rules of thumb with which to predict how a material will crystallize, chief among which is Ostwald's rule of stages. It states that the first phase to appear upon transformation of a parent phase is the one closest to it in free energy. Although sometimes upheld, the rule is without theoretical foundation and is not universally obeyed, highlighting the need for microscopic understanding of crystallization controls. Here we study in detail the crystallization pathways of a prototypic...

Cross-streamline migration of a semiflexible polymer in a pressure driven flow

Experiments and simulations on single α-actin filaments in the Poiseuille flow through a microchannel show that the center-of-mass probability density across the channel assumes a bimodal shape as a result of pronounced cross-streamline migration. We reexamine the problem and perform Brownian dynamics simulations for a bead-spring chain with bending elasticity. Hydrodynamic interactions between the pointlike beads are taken into account by the two-wall Green tensor of the Stokes equations. Our s...

By molecular dynamics simulation of a coarse-grained bead-spring-type model for a cylindrical molecular brush with a backbone chain of N_b effective monomers to which with grafting density σ side chains with N effective monomers are tethered, several characteristic length scales are studied for variable solvent quality. Side chain lengths are in the range 5 ⩽ N ⩽ 40, backbone chain lengths are in the range 50 ⩽ N_b ⩽ 200, and we perform a comparison to results for the bond fluctuation model on the simple cubic lattice (for which much longer chains are accessible, N_b ⩽ 1027, and which corresponds to an athermal, very good, solvent). We obtain linear dimensions of the side chains and the backbone chain and discuss their N-dependence in terms of power laws and the associated effective exponents. We show that even at the theta point the side chains are considerably stretched, their linear dimension depending on the solvent quality only weakly. Effective persistence lengths are extracted both from the orientational correlations and from the backbone end-to-end distance; it is shown that different measures of the persistence length (which would all agree for Gaussian chains) are not mutually consistent with each other and depend distinctly both on N_b and the solvent quality. A brief discussion of pertinent experiments is given.

Article Outline

INTRODUCTION
MODEL AND SIMULATION METHOD
SIDE-CHAIN AND BACKBONE LINEAR DIMENSIONS AND ATTEMPTS TO EXTRACT “THE” PERSISTENCE LENGTH OF BOTTLE-BRUSH POLYMERS
CONCLUSIONS

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KEYWORDS and PACS

Keywords

bonds (chemical), macromolecules, molecular dynamics method, polymer blends, solvent effects

PACS

36.20.Hb

Configuration (bonds, dimensions)
31.15.xv

Molecular dynamics and other numerical methods
31.70.Dk

Environmental and solvent effects

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http://dx.doi.org/10.1063/1.3656072

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0021-9606 (print)

1089-7690 (online)

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American Institute of Physics

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