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SUMMARY:Reconsidering old questions with new simulation techniques: Fluctu
 ations and Frank constants in polymeric liquid crystals - Dr. Kostas Daoul
 as\, Max Planck Institute for Polymer Research\, Mainz\, Germany
DTSTART:20150130T120000Z
DTEND:20150130T130000Z
UID:TALK55856@talks.cam.ac.uk
CONTACT:Dr. Judith B. Rommel
DESCRIPTION:Describing properties of mesoscale order in polymeric liquid c
 rystals (LC) has attracted considerable attention [1-4]\, partially due to
  unusual behaviour of correlation functions (e.g. “bow-tie” shape of d
 ensity structure factor). This behaviour stems from coupling between varia
 tions in density and orientation of director\, induced by polymer chain co
 nnectivity. For polymer nematics several analytical theories have been pro
 posed\, describing fluctuation spectra and related elastic constants. Intr
 iguingly\, some theoretical predictions are very controversial. The depend
 ence of the splay constant on chain length is a well-known example\, where
  linear [2-4] and quadratic [1] growth was predicted. Currently\, apart fr
 om fundamental scientific interest\, understanding mesoscale order and ass
 ociated material constants\, becomes practically important in view of nove
 l applications of polymeric LC mesophases\, e.g. in organic electronics [5
 ].\n\nThe presentation focuses on validation of theories mentioned above\,
  with efficient Monte Carlo simulations [6]. For this purpose\, polymer ne
 matics are described through a worm-like chain model combined with soft an
 isotropic non-bonded interactions. The latter are motivated by a framework
  akin to classical density functional theory of liquids. To obtain a reali
 stic model and facilitate comparison with potential experiments\, the para
 meters are chosen to reproduce persistence length and density typical for 
 poly(3-alkylthiophenes) ─ a representative family of conjugated polymers
  where LC mesophases have been reported [7]. We demonstrate that early ana
 lytical theories indeed can describe several features of fluctuation spect
 ra obtained in the simulations. Material constants controlling density and
  director fluctuations are extracted and compared with theoretical predict
 ions. The simulation results support analytical theories predicting a line
 ar dependence of splay constant on chain length.\n\nReferences:\n\n[1] P.G
 . de Gennes\, Polymer Liquid Crystals\, ch. 5\, New York: Academic Press (
 1982)\n[2] R.B. Mayer\, Polymer Liquid Crystals\, ch. 6\, New York: Academ
 ic Press (1982) \n[3] D.R. Nelson\, Physica A (1991)\, 177\, 220 \n[4] R.D
 . Kamien\, P. Le Doussal\, and D.R. Nelson\, Phys. Rev. A (1992)\, 45\, 87
 27\n[5] N. Stingelin\, Polym. Int. (2012)\, 61\, 866\n[6] P. Gemünden and
  K.Ch. Daoulas\, Soft Matter (2015)\, 11\, 532 \n[7] V. Ho\, B.W. Boudouri
 s\, and R.A. Segalman\, Macromolecules (2010)\, 43\, 7895\n
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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