Biaxial nematic phases in amphiphilic systems

Isotropic-nematic phase separation in asymmetrical rod-plate mixtures

“…For symmetrical mixtures, i.e., in case the excluded volumes of all particle pairs are set equal, the biaxial phase appears to be a commonly established feature in many theoretical studies. [8][9][10][11][12][13] Under certain conditions, the biaxial phase may, however, be unstable with respect to demixing into the separate uniaxial nematic phases, one containing predominantly rods ͑the N ϩ -phase͒ and platelets ͑the N Ϫ -phase͒. 14,15 In case of asymmetrical mixtures, i.e., mixtures for which the excluded volume of the platelets is much larger than that of the rods, there is strong experimental evidence of this demixing transition.…”

External magnetic field-dependent tricritical points of uniaxial-to-biaxial nematic transition

“…The biaxial nematic (N B ) phase, theoretically predicted by Freiser [1,2] and experimentally discovered by Saupe and co-workers [3,4] has D 2h point group symmetry. Such phase is characterized by three orthonormal directors,l;m andn ðn Dl £mÞ.…”

“…The N C U states occur for rod-like molecules with positive optical anisotropy whereas the N À U states, in general, consist of disk-like molecules with negative optical anisotropy. [3,4] In a binary mixture of oblate and prolate molecules, two types of nematic order, N C U and N À U , can form a stable biaxial nematic (N B ) phase. [15À17].…”

On a new topology in the phase diagram of biaxial nematic liquid crystals

“…n i ͑r ជ͒ and m i ͑r ជ͒ are orthogonal eigenvectors of Q ij corresponding to eigenvalues 2 3 S͑r ជ͒ and − 1 3 S͑r ជ͒ + ͑r ជ͒, respectively.…”

“…Increased interest in the theory of the N B phase was stimulated by the experimental discovery of N B phase in lyotropic mixture of potassium laurate, decanol, and water by Saupe and co-workers. [1][2][3] They showed that over a limited concentration range three distinct nematic phases are stable: two uniaxial ͓N U + ͑prolate͒ and N U − ͑oblate͔͒ and one biaxial ͑N B ͒, which merge at a four-phase "Landau" point 4 with the high temperature isotropic phase. The N U + -N B and N U − -N B transitions appear to be second order followed by a first order uniaxial-isotropic phase transition.…”