Regensburg 2022 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Crystallization, Nucleation and Self-Assembly

CPP 41.4: Vortrag

Donnerstag, 8. September 2022, 16:00–16:15, H39

Aggregation and ordering in small alkane systems — •Timur Shakirov and Wolfgang Paul — University of Halle, Halle, Germany

Ordering of small alkanes differs drastically from the bulk one. The difference is not only quantitative but also qualitative: short-chain single alkanes fold at low temperatures into non-trivial structures [1] in contrast to fully-stretched-chain lamellae in bulk. For the few chain systems we demonstrate the leading role of torsional stiffness in the ordered structure formation and investigate the corresponding conformations, which vary from spirals to tilted lamellae. For the fully stretched chain lamellae we find a two-step ordering, the indications of which remain at least up to 16 chain aggregates. In contrast to the low-temperature ordering, the aggregation or liquid-vapor transition leads to similarly disordered structures for all system sizes, which allows correction of size effects and extrapolation of the estimated aggregation temperatures to the thermodynamic limit. Our calculations of aggregation/boiling temperatures at normal pressure are in good agreement with experimental data. The presented equilibrium results are based on Wang-Landau-type Monte Carlo simulations [2,3] of a chemically realistic united atom model [4].

[1] T. Shakirov, and W. Paul, J. Chem. Phys. 2019, 150, 084903.

[2] F. Liang et al, J. Am. Stat. Assoc. 2007, 102, 305-320.

[3] T. Shakirov, Comp. Phys. Commun. 228 (2018), 38-43.

[4] W. Paul, D. Y. Yoon, and G. D. Smith, J. Chem. Phys. 103 (1995) 1702-1709.