Ferroelectric nanoparticles in liquid crystals: Role of ionic transport at small nanoparticle concentrations

We reveal an apparent influence of ultra-small concentrations (1 wt.% or less) of BaTiO3 nanoparticles (average size of 24 nm) on the current-voltage characteristics and capacitance of dielectric liquid crystal (LC) 5CB. A pure LC cell demonstrates higher current (and, hence, smaller resistance) as compared to LC cells filled with very small concentrations (0.5 and 1 wt.%) of BaTiO3 nanoparticles. The same trend is observed for the charge-voltage characteristics: the capacitance loop is the widest for the pure LC cell and becomes noticeably thinner in the presence of 0.5 and 1 wt.% of BaTiO3 nanoparticles. This seems counterintuitive, because 1 wt.% of ferroelectric nanoparticles modify the effective dielectric response very slightly and therefore should not influence on the director distribution and elastic properties of the LC. We conclude that a possible physical reason of this observation is the influence on the ionic transport in the LC of the ionic-electronic screening charges, which cover the ferroelectric nanoparticles and become polarized in an external field.