Twist-bend nematic phases in binary mixtures of banana-shaped liquid crystalline molecules

We present a mean field theory to describe twist-bend nematic (N-TB) phases in binary mixtures of banana shaped, such as bent-core or dimer, liquid crystalline (LC) molecules with K-22 > K-33, where K-22 is a twist and K-33 is a bend elastic constant. We introduce the free energy for the mixtures by taking into account the director-pitch (DP) coupling gamma(i) of the consisting LC molecules i(= A, B) and calculate the phase diagrams on the temperature-concentration plane. Our theory demonstrates that the isotropic (I), or para-nematic (pN), nematic (N), and N-TB phases appear, depending on the strength of the DP coupling parameter.i and predicts various phase transitions: the first-order N - pN(I) and N-TB - pN(I) transitions, and the second-order N-TB - N transition, etc., on the temperature-concentration plane. Our theory has a good agreement with the experimental phase diagrams of the mixtures. [Graphics] .