Study of pentyl-cyanobiphenyl nematic doped with gold nanoparticles

We studied the dispersion of up to 20 wt% gold nanoparticles (GNP) in a room temperature nematic: cyanobiphenyl homologue 4′-pentyl-4-biphenylcarbonitrile (PBPCN or 5CB). At 15% GNP, the threshold voltage decreases to 1.2 times its value for the pure nematic and the switching-off time decreases by a factor of three. We show that this decrease of display parameters is caused by a 1.8 times decrease in dielectric anisotropy, a 1.3 times change in the average elastic parameter, and a change of about 4.6 times the rotational viscosity. The doped GNP did not affect the thermal stability of the material's nematic phase and the material parameters behaviour versus gold concentration was different from the reported earlier analogical behaviour for another cyanobiphenyl homologue, 4′-hexyl-4-biphenylcarbonitrile (HBPCN or 6CB). We propose that these observed differences between the properties of two homologues doped with gold are due to differences in the number of carbon atoms in the alkyl fragment of liquid crystal molecules.