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Effect of trans-cis photoisomerization on phase equilibria and phase transition of liquid-crystalline azobenzene chromophore and its blends with reactive mesogenic diacrylate

Namil Kim1, Quan Li2, and Thein Kyu1,*

  • 1Department of Polymer Engineering, University of Akron, Akron, Ohio 44325, USA
  • 2Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA

  • *Author to whom all correspondence should be addressed: tkyu@uakron.edu
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Phys. Rev. E 83, 031702 – Published 10 March, 2011

DOI: https://doi.org/10.1103/PhysRevE.83.031702

Abstract

Photoisomerization-induced phase transition of neat liquid-crystalline azobenzene chromophore (LCAC) and its effect on phase diagrams of its mixtures with reactive mesogenic diacrylate monomer (RM257) have been investigated experimentally and theoretically. Upon irradiation with ultraviolet light, the nematic phase of LCAC transformed to isotropic, while the crystal phase showed corrugated textures on the surface (i.e., ripples). The phase-transition temperatures and corresponding morphologies of the blends have been investigated by means of differential scanning calorimetry and optical microscopy. A theoretical phase diagram of a binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe, and phase-field theory. The calculation revealed various coexistence regions such as nematic + liquid (N1 + L2), crystal + liquid (Cr1 + L2), crystal + nematic (Cr1 + N2), and crystal + crystal (Cr1 + Cr2) over a broad range of compositions including the single-phase nematic (N1, N2) of the corresponding constituents. The calculated liquidus lines were in good accord with the depressed mesophase-isotropic transition points. The present paper demonstrates the effect of trans-cis photoisomerization on the mesophase transitions of neat LCAC and the phase diagram of LCAC-RM257 as well as on the ripple formation (i.e., periodic undulation) on the azobenzene crystals.

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Phys. Rev. E 83, 031702– Published 10 March, 2011
  • Received 26 July 2010

© 2011 American Physical Society

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