Abstract
Polyethylene (PE) telechelics with carboxylate functional groups at both ends have been shown to assemble into hexagonal nanocrystal platelets with a height defined by their chain length in basic CsOH-solution. In this coarse grained (CG) simulation study we show how properties of the functional groups alter the aggregation and crystallization behavior of those telechelics. Systematic variation of the parameters of the CG model showed that important factors which control nanoparticle stability and structure are the PE chain length and the hydrophilicity and the steric demand of the head groups. To characterize the aggregation process we analyzed the number and size of the obtained aggregates as well as intramolecular order and intermolecular alignment of the polymer chains. By comparison of CG and atomistic simulation data, it could be shown that atomistic simulations representing different chemical systems can be emulated with specific, different CG parameter sets. Thus, the results from the (generic) CG simulation models can be used to explain the effect of different head groups and different counterions on the aggregation of PE telechelics and the order of the obtained nanocrystals.
Highlights
Controlling the shape, size and surface properties of nanoparticles is one of the key challenges in modern materials chemistry
To investigate the influence of the properties of func-tional groups (FGs) on aggregation and crystallization of PE telechelics, the spatial demand of the FG and the FG-water interaction strength were varied for two chain lengths and different system setups
Features of the resulting aggregates that were analyzed are among others: aggregate size distribution, end-to-end distances and internal order, local nematic order, i.e. alignment of neighboring chains and radial distribution functions (RDFs)
Summary
Controlling the shape, size and surface properties of nanoparticles is one of the key challenges in modern materials chemistry. Long chain telechelics formed nanocrystals with carboxylate FGs and caesium counter ions and with sulfonate FGs and sodium counter ions. With the sodium sulfonate FGs on the long telechelics, smaller and less well defined nanocrystals were found compared to the caesium carboxylate system. Atomistic simulations confirmed the nanoparticle structure made up by a crystalline core of regularly arranged stretched hydrocarbon chains with FGs on the platelet surfaces. Atomistic models are limited due to their comparatively high resolution This makes them computationally quite costly, which discourages their use in studies on larger spatial and temporal scales. The systems were analyzed for their aggregation behavior and the formation of ordered nanoparticles as a function of hydrophilicity and spatial demand of the FGs. In a second step, the relationship between the stability of preassembled nanocrystals and the FG parameters was studied. Comparison of CG and atomistic simulation data allowed to establish a relationship between the CG models and the different chemical systems studied experimentally and by atomistic simulations
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