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Currently, clear guidance is not available for determining the minimum practical chain lengths needed for achieving reasonable convergence when performing atomistic simulations of common synthetic polymers. Here, we analyze a collection of polymers, including polypropylene (PP), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyethylene glycol (PEG), poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyvinyl chloride (PVC), with chain lengths varying from 5 to 240 repeat units. We exclusively focus on solvated polymer systems, and we report the convergence of several characteristic properties, such as radial distribution functions (RDFs), surface area per repeat unit (SASA/N), ratio of mean squared end-to-end distance to mean squared radius of gyration ($\displaystyle{{\left\langle {R^2} \right\rangle } \over {\left\langle {R_g^2 } \right\rangle }}$ 〈 R 2 〉 〈 R g 2 〉 ), and surface electrostatic potential distributions. Based on these data, we propose a general relationship for identifying minimum practical chain lengths for performing atomistic simulations of solvated linear synthetic polymers, which is based on the SASA/N. [ABSTRACT FROM AUTHOR]

The effects of length and content of chain branching on the mechanical properties of polyethylene (PE) in atomic scale were examined by molecular dynamics (MD) simulations. Methyl-, ethyl- and butylgroups were adopted as branched chains to distribute along PE backbones. Plastic flow deformation was captured by providing a uniaxial tensile loading at a given strain rate, which shows the characteristic of rate dependence. Current results are in reasonable agreements with existing experimental data. The statistical results show that the longer length of chain branching induces lower equilibrium density and higher yield strength of branched PE. In addition, higher content of chain branching brings higher equilibrium density and lower yield strength of branched PE. It is assumed that the distribution of dihedral angles influences the deformation of PE definitely. The non-bond interactions contribute to the load-bearing capacity of PE largely. Branched PE shows big differences on mechanical behaviours comparing with the linear one. Chain branching distribution also greatly affects the performance of PE, which needs a further discussion. [ABSTRACT FROM AUTHOR]

Interaction between nanoparticles (NPs) and pulmonary surfactant monolayer plays a very significant role in nanoparticle-based pulmonary drug delivery system. Previous researches have indicated that different properties of nanoparticles can affect their translocation across pulmonary surfactant monolayer. Here we performed coarse-grained molecular dynamics simulation aimed at nanoparticles’ surface charge density effect on their penetration behaviours. Several hydrophilic nanoparticles with different surface charge densities were modelled in the simulations. The results show that NPs’ surface charge density affects their translocation capability: the higher the surface charge densities of NPs are, the worse their translocation capability is. It will cause the structural changes of pulmonary surfactant monolayer, and inhibit the normal phase transition of the monolayer during the compression process. Besides, charged NPs can be adsorbed on the surface of the monolayer after translocation as a stable state, and the adsorption capability of NPs increases generally with the increase of surface charge densities. Our simulation results suggest that the study of nanoparticle-based pulmonary drug delivery system should consider the nanoparticles’ surface charge density effect in order to avoid biological toxicity and improve efficacy. [ABSTRACT FROM PUBLISHER]