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SUMMARY:Topological transformations in foams and liquid crystalline mesoph
 ases - Oguey\, C (LPTM\, university of Cergy-Pontoise)
DTSTART:20140226T141500Z
DTEND:20140226T143500Z
UID:TALK51108@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Topological transformations such as neighbour switches or bubb
 le extinction play an important role in foams. They contribute to the onse
 t of disorder during coarsening or flow\; they provide fast elementary mec
 hanisms for dissipation\; they explain\, to a large extent\, the particula
 r visco-plastic response of foams and similar mesophases. Geometrically\, 
 topological moves provide elementary steps to pass from one structure to a
 nother\, and so offer the possibility to design new models from know templ
 ates. \n\nThe 3-arm star shaped molecules --sometimes called mikto arm pol
 ymers or linactant-- with mutually non-miscible branches self-assemble in 
 a variety of morphologies\, giving rise to a rich phase diagram. The model
 s for these mesophases can be interpreted as partitions of space into thre
 e coloured domains satisfying particular rules. The molecular cores aggreg
 ate along triple lines at the junction of the three coloured domains. \n\n
 The topological transformations occur when two or more triple line segment
 s come into contact\, generating an unstable vertex. We will see the physi
 cal reason for this instability. We will also analyse the various ways int
 o which a vertex can relax. The simplest cases can be explored systematica
 lly\, but the complexity increases rapidly. We will consider the ingredien
 ts of a possible classification. The vertex type is characterised by a sph
 ere pattern\, induced by the 3-coloured partition on a small sphere surrou
 nding the vertex. The class of sphere patterns can be spanned by operating
  2D elementary topological transformations compatible with the colouring. 
 \n
LOCATION:Seminar Room 1\, Newton Institute
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