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SUMMARY:Light structuring of functional polymers - Dr. Carlos Sánchez\, U
 niversity of Zaragoza\, Spain
DTSTART:20100429T133000Z
DTEND:20100429T143000Z
UID:TALK23939@talks.cam.ac.uk
CONTACT:Dr. Z Chen
DESCRIPTION:The use of light to locally modify polymer morphology allows t
 he implementation of structures with feature sizes in the micrometer range
 . Surface relief or three dimensional complex structures can be obtained b
 y using light structuring techniques such as mask or holographic photolith
 ographies or direct laser writing in the appropriate polymeric materials. 
 These structures have demonstrated to be of great importance in the fabric
 ation of optical elements and devices for information and communication te
 chnologies and more recently are being studied as scaffolds for cell and t
 issue growth with applications in biomedicine and regenerative medicine. T
 he work within this area carried out in the Liquid Crystals and Polymers G
 roup in Zaragoza will be presented in this talk through several examples.\
 n\nOur work carried out in the field of polarization converters will be fi
 rst presented. These systems are able to transform a linearly polarized be
 am into a radially polarized one and have potential application in tightly
  focused beam technologies such as optical storage\, photolithography or m
 icroscopy. By properly rubbing planar polyimide films it is possible to bu
 ild a LC cell able to implement this optical function. Light structuring o
 f linear photopolymerizable polymers (LPPs) can also be used as an alterna
 tive to produce complex LC command surfaces to produce these elements. Bas
 ed on liquid crystal technology\, we can generate a simple\, compact and m
 echanically robust polarization converter device. \n\nThe talk will then f
 ocus on our work on azobenzene containing polymers. These materials underg
 o isomerization-reorientation processes when they are irradiated with ligh
 t in their absorption bands. Under irradiation with linearly polarized blu
 e or green light (e.g.: 488 nm) a preferential orientation of the azobenze
 ne units with their axes perpendicular to the polarization direction of th
 e exciting light is induced. This results in macroscopic optical anisotrop
 y making these polymers potential candidates to be used as optical storage
  media. Holographic patterned irradiation of films of these materials has 
 been performed to record phase gratings based on these reorientation pheno
 mena although surface relief gratings due to mass transport have also been
  found. Traditionally these studies have been limited to Raman Nath thin g
 ratings due to the large optical absorption coefficient of azobenzene unit
 s at the recording wavelengths that hinders the effective sensitization of
  the deep layers of thick films. To fully exploit the advantages of volume
  holography thick polymeric films (in the range of 100 µm to 1 mm) with l
 ow optical absorption need to be prepared. In order to get a lower optical
  absorption\, the azobenzene content has to be diluted. This can be achiev
 ed by copolymerization of the azo monomer with others that do not absorb a
 t the wavelength of illumination. We have explored the optical response bo
 th random and block copolymers in which the azobenzene content is diluted 
 being possible to obtain thicker films with suitable absorption at the rec
 ording wavelength. Block copolymers show nanosegregated morphologies in wh
 ich azobenzene chromophores are in close interaction favoring in general t
 he stabilization of the photoinduced orientation. The influence of the mol
 ecular architecture in the phase segregated morphology and in the photoind
 uced optical properties has been studied. Holographic recording and multip
 lexing of different holograms have also been performed in thick films of t
 hese materials.\n\nReferences:\n\nS.Hvisted\, C. Sánchez\, R. Alcalá\; T
 he volume holographic optical storage potential in azobenzene containing p
 olymers\, Journal of Materials Chemistry\, 19\, 6641-6648 (2009).\n
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
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