Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 38: Computational Physics of Soft Matter I

CPP 38.8: Invited Talk

Wednesday, March 18, 2015, 11:45–12:15, C 264

Answering old questions with new simulation methods: what is the behavior of fluctuation spectra and Frank constants in polymer nematics? — •Kostas Daoulas and Patrick Gemünden — Max-Planck-Institut für Polymerforschung, Mainz, Germany

Long wavelength behavior of dense polymer nematics has attracted considerable attention from the physics community due to intriguing features. In contrast to liquid crystals (LC) with small molecules, linking mesogenes into polymer chains leads to long-range coupling of density and director fluctuations. Thus related correlation functions exhibit unusual behavior, the "bowtie shape" of the density structure factor being a characteristic example. Several analytical theories have been developed, describing fluctuation spectra and related elastic constants (e.g. Frank constants). Interestingly, some of the theoretical results are very controversial. The growth of the splay constant with chain length is a well-known example, where linear (Meyer, 1982) and quadratic (de Gennes, 1982) dependencies were predicted.

In this study we validate early analytical theories employing efficient Monte Carlo simulations of polymer nematics described by a worm-like chain model combined with soft anisotropic non-bonded interactions. We demonstrate that the analytical theories indeed can capture several features of the fluctuation spectra calculated from simulation data. Based on these spectra, elastic constants are extracted and compared with theoretical predictions. Our results are found to support strongly the theories proposing a linear dependence of splay constant on chain length.