Abstract
We present results, from Monte Carlo (MC) simulations, on polymer systems of freely jointed chains with spherical monomers interacting through the square well potential. Starting from athermal packings of chains of tangent hard spheres, we activate the square well potential under constant volume and temperature corresponding effectively to instantaneous quenching. We investigate how the intensity and range of pair-wise interactions affected the final morphologies by fixing polymer characteristics such as average chain length and tolerance in bond gaps. Due to attraction chains are brought closer together and they form clusters with distinct morphologies. A wide variety of structures is obtained as the model parameters are systematically varied: weak interactions lead to purely amorphous clusters followed by well-ordered ones. The latter include the whole spectrum of crystal morphologies: from virtually perfect hexagonal close packed (HCP) and face centered cubic (FCC) crystals, to random hexagonal close packed layers of single stacking direction of alternating HCP and FCC layers, to structures of mixed HCP/FCC character with multiple stacking directions and defects in the form of twins. Once critical values of interaction are met, fivefold-rich glassy clusters are formed. We discuss the similarities and differences between energy-driven crystal nucleation in thermal polymer systems as opposed to entropy-driven phase transition in athermal polymer packings. We further calculate the local density of each site, its dependence on the distance from the center of the cluster and its correlation with the crystallographic characteristics of the local environment. The short- and long-range conformations of chains are analyzed as a function of the established cluster morphologies.
Highlights
The phase behavior of general atomic and particulate systems has a major influence on the macroscopic properties of the end materials
In the past we explored the salient features of entropically-driven, athermal polymer crystallization through extensive Monte Carlo (MC)
Asmentioned mentionedabove, above,initial initialconfigurations configurationsare aregenerated generatedas asconfigurations configurationsof ofchains chainsof oftangent tangent hard spheres in the bulk: 100-chain
Summary
The phase behavior of general atomic and particulate systems has a major influence on the macroscopic properties of the end materials. An important difference with respect to athermal packings at high density [22,23,24,27] and quenched bulk LJ chain systems [62] is that the system studied here is highly heterogeneous and monomers that lie on the external surface of the cluster possess incomplete neighbor environments, i.e., a coordination number lower than in a crystal, so that the CCE norm attains unrealistic high values This affects the calculation of the degree of crystallinity as the ratio of the close packed sites by the total population (EquationVoronoi (2)).
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