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SUMMARY:Simulations of bent core molecules using molecular dynamics - Stok
 es\, C (University of Manchester)
DTSTART:20130322T140000Z
DTEND:20130322T142000Z
UID:TALK44076@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The nematic phase is normally uniaxial  i.e. there is just one
  distinct optical axis. In such a phase one set of molecular axes are alig
 ned but the other axes are orientationally disordered. In 1970\, however\,
  Freiser showed that a biaxial nematic phase was theoretically possible\, 
 in which all three molecular axes are aligned. This phase has since been o
 bserved experimentally\, predicted to exist theoretically for various part
 icle models and has been seen in simulation studies. Such a phase would ha
 ve three distinct optical axis and there are possible applications to liqu
 id crystal displays\, should a suitable material be found. In this talk I 
 would like to present the results of simulation studies on purely repulsiv
 e bent-core models (V-shaped particles). In the limit of very long\, thin 
 arms\, such shapes have been predicted to exhibit a biaxial nematic phase 
 for bend angles in the region of 110o. In order to test these predictions 
 and also to explore the systems pha se behaviour at pressures at which the
  nematic phase is unstable\, we have run molecular dynamics simulations fo
 r one-component systems\, binary mixtures and higher order mixtures (4  6 
 components). In all case the runs started from the isotopic phase and the 
 system\, was then slowly compressed\, so any phase observed had formed spo
 ntaneously. We explored the effects of varying the arm lengths and bend an
 gles of these particles on the phase behaviour. For a one-component system
 \, only particles with bend angles greater than ca. 130o spontaneously for
 med ordered\, equilibrated phases. Typically the phase sequence was isotro
 pic →uniaxial nematic→biaxial smectic A (except for very straight part
 icles in which the smectic phase was uniaxial). No biaxial nematic phase w
 as observed for the arm-lengths simulated. It is possible that if the smec
 tic phase could be destabilized\, a biaxial nematic might form in its plac
 e. Such destabilization might occur in mixtures. Binary mixtures of bent c
 ores\, however\, were found.\n\n
LOCATION:Seminar Room 1\, Newton Institute
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