Liquid crystal composites with a high percentage of gold nanoparticles

We have reported in our previous work that doping low concentrations (up to 10% by weight) of gold nanoparticles (GNP) in a polar nematic 4'-hexyl-4-biphenylcarbonitrile (HBPCN) increases the dielectric anisotropy, while the switching voltage and times, and the nematic-isotropic liquid (IL) transition point of the mixtures are not affected by doped nanoparticles. In the current work we extend our study of the behaviour of HBPCN doped with higher than 10% GNP. We show that at certain gold concentrations - 35% and 45% - the nematic-IL phase transition point increases by 15°C in comparison with the pure nematic value. At the same concentrations the dielectric anisotropy increases from its value for the pure nematic by about 2.2 times for 35% and twice for 45%. Also, the threshold voltage increases by 0.2 V for 35% and decreases by 0.15 V for 45%. However, the switching-off times decrease for both concentrations: 7 ms for 35% and 12 ms for 45%.We propose that the described effects of doped GNP on the properties of the nematic are due to the formation of different kinds of aggregations between two components of the mixtures.