Glass-like Behavior at Molecular Level Induced in a Nematic by a Dispersion of Aerosil Nanoparticles

ABSTRACT

Random disorder effects of an hydrophobic aerosil on the order and dynamics of the 3β-DOXYL-5α-cholestane spin probe in the liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) were studied using the ESR technique. Increasing the aerosil concentration up to 10 wt% does not change the nematic–isotropic transition temperature but decreases the probe order parameter. The dynamics in the isotropic phase is of Arrhenius type and essentially independent of the concentration. Deviations from this behavior are clearly observed in the nematic phase even at 1 wt% of aerosil and are well represented by a Vogel-Fulcher-Tammann type law, suggesting that a glass-like behavior can be induced by a very small amount of random disorder.

PACS numbers: 61.30. Gd, 76.30.-v, 82.70. Gg

Keywords:

• ESR spin probe
• filled nematics
• hydrophobic aerosil
• non Arrhenius dynamics
• random disorder

Acknowledgments

We thank MURST (PRIN “Cristalli Liquidi”), INSTM and the University of Bologna for support. We also thank Degussa for the generous gift of a sample of the R812 aerosil.