  Twist-bend (Ntb) and ferroelectric (NF) nematic liquid crystals exhibit
several novel effects and new physical properties. The question of what happens
in binary mixtures is interesting as a matter of curiosity and pure science.
Here, we report experimental studies on the phase diagram and some physical
properties of binary mixtures of the above-mentioned nematic liquid crystals.
Both N-Ntb and N-NF phase transition temperatures and the corresponding
enthalpies decrease significantly and eventually, these transitions disappear
in some intermediate compositions. Temperature dependent birefringence above
the N-Ntb phase transition temperature shows critical behaviour, and the
critical range of the tilt fluctuations becomes wider in the mixtures. The
magnitudes and the temperature dependence of the splay elastic constant of the
mixtures' high-temperature nematic (N) phase strikingly differ from that of the
pristine twist-bend and ferroelectric nematic liquid crystals. The study shows
that Ntb and NF liquid crystals are incompatible.
