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SUMMARY:A molecular model for the electroclinic effect in nematic liquid c
 rystals - Greco\, C (Universit degli Studi di Padova)
DTSTART:20130322T142000Z
DTEND:20130322T144000Z
UID:TALK44082@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The electroclinic effect (ECE) is an electro-optical effect th
 at consists in a tilt of the optical dielectric tensor of a liquid crystal
  (LC) material upon application of an external electric field. The tilt is
  linear in the electric filed\, and the proportionality coefficient\, the 
 electroclinic coefficient\, is a property of the LC material. Originally o
 bserved in the orthogonal smectic-A phase made of chiral molecules (smecti
 c-A* phase)[1]\, the ECE effect was subsequently also measured in the heli
 x-unwound nematic N* phase [2]\, thus demonstrating that smectic layering 
 is not essential for its appearance. Recently it was also measured in nema
 tic LCs made of non-chiral molecules\, upon imposition of an external mech
 anical twist [3]. The origin of the ECE in nematics is not obvious\, and d
 ifferent molecular/environmental contributions have been proposed over the
  years. We have developed a molecular model for the ECE in nematics. Based
  on the molecular and phase symmetry\, we hav e obtained expressions of th
 e EC coefficient as a function of the relevant molecular properties (dipol
 e moment\, polarizability). The use of an atomistic representation of the 
 molecular shape\, charges and polarizability allows us to analyze the rela
 tionship between the ECE and the molecular structure. We will present some
  examples and discuss the role of the molecular and phase chirality. \n\n[
 1] Garoff. S.\; Meyer R. B. Phys. Rev. Lett. 1977\, 38\, 848-851. [2] Li\,
  Z.\; Petschek\, R. G.\; Rosenblatt\, C. Phys. Rev. Lett. 1989\, 62\, 796-
 799. [3] Basu\, R.\; Pendery\, J. S.\; Petschek\, R.G.\; Lemieux\, R. P.\;
  Rosenblatt\, C. Phys. Rev. Lett. 2011\, 107\, 237804: 1-4. \n\n
LOCATION:Seminar Room 1\, Newton Institute
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