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SUMMARY:Kinetics of Light-Induced Patterning in Liquid Crystal Elastomers 
 (**joint talk with I-CAMP) - Copic\, M (University of Ljubljana)
DTSTART:20130628T134500Z
DTEND:20130628T143000Z
UID:TALK45967@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Liquid crystal elastomers doped with molecules that change con
 formation on absorption of a photon show very large changes photoelastic r
 esponse. This can be investigated by recording a holographic grating  in t
 he material with the use of two crossed UV laser beams. Angular dependence
  of the diffraction efficiency in the vicinity of the Bragg peak can be an
 alyzed using a numerical model that takes into account the propagation of 
 writing beams and rate equations for the local concentration of the absorb
 ing trans conformer\,  and spatial distribution of the trans and cis confo
 rmers  can be obtained. Stress dependence on the irradiation time can be a
 nalyzed in a similar way.  Strongly nonlinear relationship between the con
 centration of the cis isomers of the azomesogens and the refractive index 
 modification of the material\, which is characteristic for the phase trans
 ition region\, results in non-monotonous time dependence of the diffractio
 n efficiency of a probe beam. From this effect  the sensitivity of the nem
 atic transition temperature on the molar fraction of the cis isomers is de
 termined. The relation between the cis isomer molar fraction and nematic o
 rder also provides a possibility for recording hidden holograms\, which ca
 n be made visible by cooling the sample from the paranematic to the nemati
 c phase. \n
LOCATION:Centre for Mathematical Sciences\, Meeting Room 2
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