Condensed Matter Physics, 2006, vol. 9, No. 1(45), p. 87-94, English

Title: Photo-induced deformations in azobenzene-containing side-chain polymers: molecular dynamics study
  J.Ilnytskyi (Institute for Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany; Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine) ,
  M.Saphiannikova (Leibniz Institute of Polymer Research, Hohe Str. 6, 01069 Dresden, Germany) ,
  D.Neher (Institute for Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany)

We perform molecular dynamics simulations of azobenzene containing side-chain liquid crystalline polymer subject to an external model field that mimicks the reorientations of the azobenzenes upon irradiation with polarized light. The smectic phase of the polymer is studied with the field applied parallel to the nematic director, forcing the {\it trans} isomers to reorient perpendicularly to the field (the direction of which can be assosiated with the light polarization). The coupling between the reorientation of azobenzenes and mechanical deformation of the sample is found to depend on the field strength. In a weak field the original smectic order is melted gradually with no apparent change in the simulation box shape, whereas in a strong field two regimes are observed. During the first one a rapid melting of the liquid crystalline order is accompanied by the contraction of the polymer along the field direction (the effect similar to the one observed experimentally in azobenzene containing elastomers). During the slower second regime, the smectic layers are rebuilt to accomodate the preferential direction of chromophores perperdicular to the field.

Key words: liquid crystals, azobenzene, polymers, molecular dynamics
PACS: 31.15.Qg, 64.70.Md, 64.70.Nd

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