Orientational Coupling Amplification in Ferroelectric Nematic Colloids

We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy, and capacitance studies. The resulting homogeneous colloids possess a significantly amplified nematic orientational coupling. We find that the nematic orientation coupling increases by $\sim 10\%$ for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases by up to $40°\mathrm{C}$ compared to the pure liquid crystal host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.

Figure 1

DSC graphs for heating and cooling of the samples with pure LC MLC-6609 (bottom pair of the curves) and colloids of ${\mathrm{BaTiO}}_3$ in MLC-6609 (top pair of the curves), $c_{\mathrm{part}}\approx 0.2\%$. Inset: TEM picture of ferroelectric nanoparticles.

Figure 2

Temperature dependences of the order parameter of MLC-6609 and the ferroelectric colloid ($c_{\mathrm{part}}\approx 0.2\%$).

Figure 3

Temperature dependence of the birefringence of MLC-6609 and the ferroelectric colloid ($c_{\mathrm{part}}\approx 0.05\%$).

Figure 4

Temperature dependences of the dielectric anisotropy of MLC-6609 and the ferroelectric colloid ($c_{\mathrm{part}}\approx 0.2\%$).