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E. P. Sokolova, A. Yu. Vlasov

Author affiliations
Department of Chemistry, St. Petersburg State University,
Universitetsky Pr., 26, 198504 St. Petersburg, Russia
E-mail: esok@AM7940.spb.edu

Abstract
We consider the effect of doping the system by long rod-shape particles (L) upon stability of a biaxial nematic (N_b) with regard to demixing into uniaxial nematics N₊ and N_- in the athermal system (R–P) of rods and plates with small aspect ratios values (γ_R = 5, γ_P = 1/5). The restricted orientation (Zwanzig) model of a multi-component system of rectangular parallelepipeds is employed, wherein collective interactions are accounted for on the level of the 3rd virial approximation. The second-order N₊–N_b and N_-–N_b phase boundaries were located numerically from the data on biaxiality parameters in the vicinity of bifurcation points, where the said quantities show up as infinitesimal. Thermodynamic stability of biaxial phases in the ternary systems was estimated from the calculated values of the Gibbs energy spanning the concentration intervals of pseudobinary (P–R) mixtures given constant mole fraction (γ_L) of component L. It is demonstrated that stabilization of the N_b phase is plausible along the sections of the composition triangles with γ_L ≥ 0,01, provided γ_L ≥ 8. The stability domain of the N_b phase expands by increasing L component particle volume while keeping γ_L fixed.

Keywords: biaxial nematic phase; the Zwanzig model; сolloidal liquid crystals;rod-plate mixtures