Spontaneous mirror symmetry breaking by formation of chiral structures from achiral building blocks and emergent polar order are phenomena rarely observed in fluids. Separately, they have both been found in certain nematic liquid crystalline phases; however, they have never been observed simultaneously. Here, we report a heliconical arrangement of achiral molecules in the ferroelectric nematic phase. The phase is thus spontaneously both polar and chiral. Notably, the pitch of the heliconical structure is comparable to the wavelength of visible light, giving selective reflection controllable by temperature or application of a weak electric field. Despite bearing resemblance to the heliconical twist-bend nematic phase, this chiral ferroelectric nematic phase arises from electrical interactions that induce a noncollinear orientation of electric dipoles.

The electroviscous effect deals with the change in the viscosity of fluids due to an external electric field. Here, we report experimental studies on the electroviscous effects in a ferroelectric nematic liquid crystal. It is synthesized by accomplishing an optimized synthetic route, which provides higher yield than the conventional one. We measure electric-field-dependent viscosity under a steady shear at different temperatures. In the low-field range, the increase in viscosity [$\mathrm{\Delta }\eta =\eta (E)-{\eta }_0$] is proportional to $E^2$ and the corresponding viscoelectric coefficient [$f\approx {10}^{-9}{\mathrm{m}}^2/{\mathrm{V}}^2$] of the ferroelectric nematic is 2 orders of magnitude larger than the apolar nematic liquid crystals and the largest ever measured for a fluid. The apparent viscosity measured under a high electric field shows a power-law divergence $\eta \sim (T-T_c{)}^{-0.7\pm 0.05}$, followed by nearly an order of magnitude drop below the $N$-$N_F$ phase transition. Experimental results within the dynamical scaling approximation demonstrate rapid growth of polar domains under a strong electric field as the $N$-$N_F$ phase transition is approached. The gigantic electroviscous effects demonstrated here are useful for emerging applications and understanding striking electrohydromechanical effects in ferroelectric nematic liquid crystals.

The design, synthesis and physicochemical properties of the highly polar ferroelectric nematic liquid crystal are reported. This compound exhibits enantiotropic N _F phase, as the very first example with such behaviour.

We investigated the influence of the DC electric field on the electrical and optical properties of a liquid crystal compound 4-(4-nitrophenoxycarbonyl)phenyl 2,4-dimethoxybenzoate, known as RM734, exhibiting a ferroelectric nematic phase.

The recent discovery of nematic liquid crystals with polar order (ferroelectric) has created immense interest. Despite intensive research, several physical properties of this liquid crystal are yet to be investigated and understood. Here, we report experimental studies on the surface alignment, birefringence, and flexoelectric coefficient of a polar nematic $\left(N_{\mathrm{F}}\right)$ liquid crystal. Our experiments directly reveal that the splay fluctuations influence the birefringence several degrees above the nonpolar $\left(N\right)$ to polar nematic $\left(N_{\mathrm{F}}\right)$ phase transition temperature, and the heat capacity exponent obtained from the tilt angle fluctuations is close to the value reported in adiabatic scanning calorimetry measurements. The flexoelectric coefficient of the nonpolar nematic phase shows a power-law dependence on temperature. It demonstrates a strong polar coupling of pretransitional ferroelectric fluctuations with the field. These results are important for applications as well as for understanding all pretransitional effects in ferroelectric nematic liquid crystals.

In soft ferroelectric crystals, the depolarization field can be reduced by a periodic distortion of the polarization direction. In the polar nematic and tilted smectic phases, this process is energetically favored, as it only requires changes in the director orientation. We demonstrate the spontaneous formation of a helical structure in the proper ferroelectric tilted smectic (SmC^H _P) phase, formed below the heliconical polar nematic (N_TBF) phase. The helical pitch in the smectic phase is approximately 600 nm and remains nearly constant across the entire temperature range of the phase. Under weak electric field, the helix reorients while its structure remains largely intact; however, in stronger field the helix is destroyed as the electric polarization aligns along the electric field.