Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 70: Crystallization, Nucleation and Self-Assembly II

CPP 70.1: Hauptvortrag

Donnerstag, 15. März 2018, 15:00–15:30, C 230

Crystallization in melts of semi-flexible hard polymer chains: An interplay of entropies and dimensions — •Wolfgang Paul and Timur Shakirov — Institut für Physik, Martin Luther Universität, 06099 Halle

Morphology selection upon crystallization of long-chain polymers is governed by an intricate and so far unresolved interplay between thermodynamic and kinetic effects. We argue, that the thermodynamic driving forces for this phase transition can be studied looking at relatively short chains as well. For a melt of short, semi-flexible polymer chains with purely repulsive intermolecular interactions, Stochastic Approximation Monte Carlo simulations can be employed to obtain the complete thermodynamic equilibrium information. Thermodynamics is obtained based on the density of states of a simple coarse-grained model, which varies by up to 5500 orders of magnitude. We show that our polymer melt undergoes a first-order crystallization transition upon increasing the chain stiffness at fixed density. The lyotropic three-dimensional orientational ordering transition drives the crystallization and is accompanied by a two-dimensional hexagonal ordering transition in the plane perpendicular to the chains. While the three-dimensional ordering can be understood in terms of Onsager theory, the two-dimensional transition is similar to the liquid-hexatic transition of hard disks. Due to the domination of lateral two-dimensional translational entropy over the one-dimensional translational entropy connected with columnar displacements, the chains form a lamellar phase.