Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

• Published in: Physical review. E, Statistical, nonlinear, and soft matter physics Vol. 83; no. 4 Pt 1; p. 041703
• Main Authors: de Jeu, Wim H, Ostrovskii, Boris I, Kramer, Dominic, Finkelmann, Heino
• Format: Journal Article
• Language: English
• Published: United States 01-04-2011
• ISSN: 1539-3755; 1550-2376
• DOI: 10.1103/PhysRevE.83.041703

We report effects of disorder due to random cross-linking on the nematic to smectic-A phase transition in smectic elastomers. Thermoelastic data, stress-strain relations and high-resolution x-ray scattering profiles have been analyzed for two related compounds with a small and a larger nematic range, respectively, each for 5% as well as 10% cross-links. At 5% cross-link density the algebraic decay of the positional correlations of the smectic layers survives in finite-size domains, providing a sharp smectic-nematic transition. At an increased cross-link concentration of 10% the smectic order disappears and gives way to extended short-range layer correlations. In this situation neither a smectic-nematic nor a nematic-isotropic transition is observed anymore. The occurrence of disorder at a relatively large cross-link concentration only, indicates that smectic elastomers are rather resistant to a random field. The temperature dependence of the correlation lengths and thermoelastic behavior suggest a shift to a "parasmectic" regime of a first-order smectic-isotropic transition.